DEGREE PROJECT IN MATERIALS SCIENCEENGINEERING, SECOND CYCLE, 30 CREDITSANDSTOCKHOLM, SWEDEN 2017

Built-up edge formation in
stainless steel milling
AXEL ANDERSSONKTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENTExamensarbete MSE MH210X 2017

Löseggsbildning vid fräsning av rostfritt stålAxel Andersson

Godkänt

Examinator

Handledare

Joakim Odqvist

Joakim Odqvist

Uppdragsgivare

Kontaktperson

Sandvik Coromant

Roland Bejjani

Sammanfattning
Fräsningstest utfördes I rostfritt stål för att undersöka bildande av lösegg. Tre testvarianter
gjordes, uppdelade i hög-, medium-, och låg frästemperatur. Dessa prov kördes i austenitiskt
rosfritt stål, SS2343. Fräsning vid mediumtemperatur gjordes även i duplexa SS2377 ochutskiljningshärdade CORRAX. Lösegg bildades vid alla tester. Med undantag för
högtemperaturstesterna bildades lösegg lokalt på huvudskäreggen. Vid hög temperastur
täckte i stället löseggen hela eggen. Alla skär, med olika skärteknologier hade samma
mängd bildad lösegg. Den initiala verktygsförlitningen var samma för alla skär, med
undantag av det PVD-beläggda skäret, som hade mindre lossnande av beläggning påskäreggen.
Tvärsnitt visade att förutom lösegg hade även smearing inträffat på skärens arbetssida,
vilket visade att vidhäftande inträffade i flera lager på skäret.Tvärsnitten visade även att
skären hade slitits likartat för de olika fräsmtoderna, trots att det var känt att verktygsfel
skulle orsakas av olika förslitningstyper.
Mikrohårdhetstester av löseggarna gav resultat där det austenitiska-, och duplexa rostfriastålet hade fördubblat sin hårdhet i jämförelse med arbetsmaterialet. Deformationshärdning
av CORRAX var lägre i genomsnitt, där dess hårdhet hade ökat med midre än 9 procent. Då
CORRAX gav samma mängd löseggsbildning som de andra stålen kunde slutsatsen dras att
arbetshärdning inte påverkade BUE-bildningen.
För ett prov fräsat vid hög temperatur hade en ny fas bildats på skärytan. Analys i EPMA och
EDS indikerade att den innehöll krom, mangan och syre. Detta indikerade att det rostfriastålet oxiderades vid fräsning vid högre temperatur. Jämförelse av kompositionen, visade att
den var likartad för lösegg och arbetsmaterialet SS2343. Det enda undantaget var att titan
kunde hittas i löseggens bulk, vid högre temperatur. Detta indikerade att löseggen hadeinteragerat med beläggningen, då det var den enda titankällan

Master of Science Thesis MSE MH210X 2017

Built-up edge formation when milling stainlesssteel

Axel Andersson

Approved

Examiner

Supervisor

Joakim Odqvist

Joakim Odqvist

Commissioner

Contact person

Sandvik Coromant

Roland Bejjani

Abstract
Milling tests were performed in stainless steel to investigate the formation of built-up edge
(BUE). Three variants of tests were conducted which were divided as high-, medium, andlow temperature milling tests. These tests were run in the austenitic stainless steel SS2343.
The medium temperature milling tests were run in duplex SS2343 and precipitation
hardened CORRAX. BUE was found for all tests. With the exception of the high temperature
milling tests, BUE was formed locally on the main cutting edge. When milling at higher
temperature the BUE covered the entire edge. All inserts used, each with different
technologies had the same amount of BUE formation. The tool wear was similar for the
CVD-coated inserts used, while the PVD-coated insert suffered less coating detachment
along the edge.
Cross sections showed that in addition to BUE, smearing had occurred on the rake face of
the inserts, showing that multiple layers of material adhered to the tool surface. Cross
sections also showed that the tool wear was similar for the different milling methods, eventhough it was known that tool failure eventually would be caused by different wear types.
Microhardness tests of the BUE gave results where the austenitic- and duplex stainless steel
had in average almost doubled their hardness. Work hardening for CORRAX was lower withan average hardness increase below 9 percent. As CORRAX gave the same amount of BUE
formation as the other steels it could be concluded that work hardening did not affect theamount of BUE formation.
For one sample milled at high temperature a new phase had formed on the insert surface.
Analysis in EPMA and EDS indicated that it contained chromium, manganese and oxygen.
This indicated that the stainless steel had oxidized when milled at higher temperature. When
comparing the composition, it was similar for both BUE and the workpiece material SS2343.
The only exception was that titanium could be found in the bulk of the BUE, having higher
amount when milled at higher temperature. This indicated that the BUE had interacted withthe coating, as this was the only source of titanium.

Foreword
I would like to give my thanks to my supervisor at Sandvik Coromant, Roland Bejjani for all
the support throughout this entire work. This was invaluable as tool wear was a new area ofwork for me. I would also like to thank Sandvik Coromant for giving me the opportunity andsupport to make this master’s thesis for them. All the help that I received from the people at
Sandvik Coromant has been invaluable and this work would be impossible without it. Lastly I
would like to thank my KTH supervisor and examiner Joakim Odqvist.

Axel Andersson
Stockholm, August 2017

Nomenclature
NotationsSymbolDescriptionvc

Cutting speedfz

Feed rate

Dc

Cutter diameter

ap

Axial cutting depthaeRadial cutting depthγRake angle

φShear plane angle

Abbreviations
BUE

Built-up edge

BUL

Built-up layer

CVD

Chemical vapour deposition

PVD

Physical vapour deposition

LOM

Light optical microscope

SEM

Scanning electron microscope

EDS

Energy-dispersive X-ray spectroscopy

EPMAElectron probe micro-analyzer

WDS

Wavelength-dispersive X-ray spectroscopy

HV

Vickers hardness

HB

Brinell hardness

Dp

Delprov (Subsample)

Table of contents
1. INTRODUCTION ................................................................................ 1
1.1 Objectives .................................................................................................................... 2
1.2 Thesis layout ............................................................................................................... 2

2. BACKGROUND .................................................................................. 4
2.1 Stainless steel ............................................................................................................. 4
2.2 Milling and machining .................................................................................................. 4
2.3 Milling parameters ....................................................................................................... 5
2.4 Machining of stainless steel ......................................................................................... 5
2.5 Cemented carbide tools ............................................................................................... 6
2.6 Wear types .................................................................................................................. 6
2.6.1 Built up edge ......................................................................................................... 6
2.6.2 Cutting edge chipping ........................................................................................... 6
2.6.3 Thermal cracking .................................................................................................. 6
2.7 Characterization equipment ......................................................................................... 7
2.7.1 Optical microscope ............................................................................................... 7
2.7.2 Scanning electron microscope (SEM) ................................................................... 7
2.7.3 Energy-dispersive X-ray spectroscopy (EDS) ....................................................... 7
2.7.4 Electron probe micro-analyzer (EPMA) ................................................................. 7
2.7.5 Focus variation...................................................................................................... 8
2.7.6 Microhardness ...................................................................................................... 8

3. LITERATURE STUDY ........................................................................ 9
3.1 BUE formation when machining stainless steel............................................................ 9
3.1.1 Formation.............................................................................................................. 9
3.1.2 Affecting factors .................................................................................................... 9
3.1.3 Effects on tool wear ............................................................................................ 10
3.1.4 Effects on machined surface ............................................................................... 10
3.2 Previous work ............................................................................................................ 10
3.2.1 Milling of stainless steel ...................................................................................... 10
3.2.2 Machining with BUE formation ............................................................................ 11
3.2.3 Effect of coating surface roughness on adhesion ................................................ 13
3.2.4 Previous tests performed at Sandvik Coromant .................................................. 14

4. METHODS ........................................................................................ 15
4.1 Inserts........................................................................................................................ 15
4.2 Workpiece materials .................................................................................................. 16
4.3 Experimental setup .................................................................................................... 16
4.4 Cross section preparation .......................................................................................... 18
4.5 Quick-stop samples ................................................................................................... 18
4.6 Characterization methods .......................................................................................... 19
4.6.1 Microhardness testing ......................................................................................... 19
4.6.2 EPMA ................................................................................................................. 19
4.6.3 Microscopy and EDS........................................................................................... 19
4.6.4 Surface roughness .............................................................................................. 20

5. RESULTS AND DISCUSSION .......................................................... 21
5.1 Observational study ................................................................................................... 21
5.1.1 Occurrence of BUE ............................................................................................. 21
5.1.2 Initial tool wear .................................................................................................... 23
5.1.2.1 Low temperature milling ........................................................................... 23
5.1.2.2 Medium temperature milling ..................................................................... 24
5.1.2.3 High temperature milling ........................................................................... 24
5.1.2.4 Milling in SS2377 (duplex) ........................................................................ 25
5.1.2.5 Milling in CORRAX (precipitation hardened) ............................................. 25
5.1.2.6 Effect of top blasting post treatment ......................................................... 26
5.1.2.7 Effect of modified Al2O3-coating ................................................................ 27
5.1.3 Cross sections .................................................................................................... 28
5.1.3.1 Tool wear ................................................................................................. 28
5.1.3.2 Appearance of BUE .................................................................................. 28
5.1.3.3 Wear of coating ........................................................................................ 30
5.1.3.4 Cross sections of tool life samples............................................................ 32
5.1.3.5 SEM analysis............................................................................................ 34
5.1.4 Quick-stop samples............................................................................................. 38
5.2 Characterization study ............................................................................................... 41
5.2.1 Microhardness tests ............................................................................................ 41
5.2.2 EPMA ................................................................................................................. 42
5.2.3 EDS .................................................................................................................... 46
5.2.3.1 Point analyses .......................................................................................... 46
5.1.3.2 Line scans ................................................................................................ 50

5.1.3.3 Additional EDS analysis ........................................................................... 52
5.2.4 Surface roughness .............................................................................................. 55

6. CONCLUSIONS ............................................................................... 57
7. RECOMMENDATIONS FOR FUTURE WORK ................................. 58
8. REFERENCES ................................................................................. 59
APPENDIX A: CUTTING PARAMETERS ............................................. 63
APPENDIX B: WORN EDGES.............................................................. 65
APPENDIX C: CROSS SECTIONS ..................................................... 69
APPENDIX D: SEM IMAGES................................................................ 74
APPENDIX E: IMAGES FOR EDS ANALYSIS .................................... 77
APPENDIX F: MICROHARDNESS RESULTS ..................................... 79

1. Introduction
Unlike iron, stainless steel is a rather new material, with little bit more than 100 years of history.
Due to its physical and chemical properties, stainless steel came to revolutionize the world. It
can now be found in almost every manufacturing sector. It has found applications from thehealthcare- to the construction- and automotive industries. Unlike many other noncorrosive
specialist materials, stainless steel is reasonably inexpensive which makes it a clear choice ofmaterial in many cases [1]. However, many applications require the material to be changed
into desired shapes. Machining is one process where the size, shape and surface of aworkpiece material is changed by mechanical removal of material. This demands the need ofproper tools. Cemented carbide is an extensively used cutting material and is the general
choice when machining stainless steel. Tool wear and eventual tool failure can however not
be avoided. Built-up edge (BUE) is one of several causes of tool wear when machining
stainless steel. Workpiece material accumulating on the tool edge. As the adhered material
work-hardens it creates a new cutting edge by itself, shifting the position of where the cut takes
place. This can lead to tool wear as when the BUE eventually breaks away, it can rip off partsof the tool with it. It is therefore important to learn about this phenomenon to understand what
problems it can cause, or to avoid it completely. Figure 1.1 [2] shows an illustration of BUE
formation and how it affects the cut, with the BUE eventually detaching.

Figure 1.1. BUE formation during metal cutting [2].

1

1.1 Objectives
The aim of this thesis work is to increase the knowledge of BUE when milling stainless steel.
Attention regarding BUE has mainly been given for turning, with a considerable lack ofliterature when it comes to milling. The work in this project has been surrounding the following
hypotheses:
A. Ability to form BUE is possible for different milling parameters and workpiece materials.
B. The BUE affects the wear differently for different insert technologies.
C. The properties of BUE differ at different milling conditions.
The means of proving/disproving these hypotheses was by providing answers to the following
research questions:

How does cutting conditions affect BUE, in terms of: Cutting temperature?
 Dry/wet cutting?
 Workpiece material?

What is the relation of BUE to wear of the cutting edge, in terms of: Post deposition top blasted coating?
 Modified alumina coating?
 The cemented carbide substrate?



Does the properties of BUE depend on cutting conditions, in terms of: Hardness?
 Composition?
 Microstructure?

1.2 Thesis layout
This thesis is divided into 7 main sections.
Section 2 describes the fundamental phenomena of stainless steel, machining and tool wear.
Basics behind equipment employed in the future parts of the thesis are described.
Section 3 is the main literature study. This is divided into two parts. The first part is regarding
BUE, its formation and effects. In the second part is a collection of previous work regarding
both milling and BUE formation of stainless steel. Previous milling tests by Sandvik Coromant
are evaluated with respect to BUE as well.
The methods of experimental design, sample preparation and characterization are describedin section 4.
The results are listed and discussed in section 5. In turn this section is divided in two mainparts; observational study and characterization study. These parts concern hypothesis A and2

B, and C respectively. Namely the occurrence of BUE and its appearance on worn tool, andthe differences in characteristics of the BUE.
All the conclusions drawn in the thesis are mentioned in section 6, with recommendations of
future work noted in section 7. Finally, the parameters, acquired results and data that is
discussed is fully presented in appendix.
The process of the work started with a literature study regarding BUE formation in milling ofstainless steel. This led to the construction of the hypotheses. To answer the researchquestions regarding the hypotheses, milling tests were performed. The formation of stainlesssteel led to further analysis, i.e. the characterization- and observational studies. These results
were analysed to answer the research questions, proving/disproving the hypotheses. The
general workflow of the thesis is presented in figure 1.2.

Figure 1.2. Chart of the employed workflow.

32. BackgroundThe underlying phenomena are explained and the background knowledge to tool wear whenmachining stainless steel.
2.1 Stainless steel
Stainless steel is a type of alloyed steel which represents its own material group. As its namesuggests these are steels that have an increased resistance to corrosion in comparison toother steels, which is their most important property. The main alloying element is chromium,
which constitutes at least 12% of the composition. The chromium protects the stainless steel
by forming an oxide layer, which inhibits further corrosion to take place. The Cr 2O3 prevents
the iron in the steel to be oxidized and thus corrosion is suppressed. Corrosion resistance isgenerally increased along with the chromium content. Chromium, which is a ferrite former,
does not change the structure of the steel, which makes stainless chromium steels have
similar properties as those of pure iron. Other alloying elements are however usually added
which can change several properties of the steel; microstructure, corrosion resistance,
strength, etc. Due to the ability to change the microstructure of stainless steels, they can bedivided into three main groups: ferritic-, martensitic-, and austenitic stainless steel. Duplex
stainless steels are part austenitic and part ferritic.
Nickel is a main constituent in austenitic stainless steel, which affects its structure andproperties. This is due to the austenitic forming ability of nickel. At high enough amounts ofnickel, the stainless steel has an austenitic microstructure at room temperature. This leads toseveral changes of its properties, such as increased corrosion resistance, high-temperaturestrength, plasticity and ductility, weldability, etc. Additionally, the stainless steel loses its
ferromagnetism [3]. For further corrosion resistance, molybdenum can be added which has
the same effect on the microstructure as chromium. This makes stainless steel corrosion
resistant in environments containing chlorides and reducing acids, hence the name acid proof
stainless steel [4].
2.2 Milling and machining
Machining is a cutting process where parts of the metal is removed from the workpiecematerial in form of chips, until a desired shape is obtained. Formation of chips is the mainelement in metal cutting. When the edge of a tool cuts a layer of the workpiece material it issheared into a chip which is thicker than the depth of cut, ae. Formation of the chip takes placein the primary shear zone. The chips are sheared further at the secondary shear zone as theyslide over the rake face of the tool. The shape of the chips depends heavily on the propertiesof the workpiece material [5]. Figure 2.1 illustrates chip formation, where φ is the shear planeangle, i.e. the angle of the primary shear zone [6]. A brittle material produces shorter chips as
it cracks easily. A ductile material, such as austenitic stainless steel produces longer orcontinuous chips. The shearing of the chips can be influenced by changing the rake angle, γ.
Increasing γ will give a higher shearing which will improve the chip-breaking ability. However,this is done at the cost of higher cutting edge temperature, cutting forces and mechanicalstress on the edge. Generally, it is required that the shape of the chips should not hinder themachining process in any way, and short, discontinuous chips are preferred [5].

4Figure 2.1 Chip formation in metal cutting [6].
Milling is a machining operation where the tool is moving in relation to the workpiece andprovides the feed motion. It is an intermittent machining process, meaning that the tool is partly
engaged in the workpiece material at every rotation of the tool. This is what makes milling acomplicated machining operation as the cutting tool is heated up at every passage in theworkpiece material and cooled down when it is not engaged. Every entrance into contact
provides additional stresses on the tool which gives high requirements of the cutting tool [5].
2.3 Milling parameters
There are several parameters that can be varied in a milling process, influencing the cutting
process. Cutting speed, vc is the speed of the cutting edge relative the workpiece and isdefined as [m/min]. Tooth feed, fz is the distance the cutter moves in relation to the workpiece
during the engagement time of one tooth. It is defined as [mm/tooth]. Dc is the diameter of themilling cutter. Additionally, there are the axial cutting depth, ap and radial cutting depth, ae[mm] [5].
2.4 Machining of stainless steel
Austenitic steel is considered a difficult-to-machine material. Machinability however, can be
defined in regards of several aspects; tool wear, surface roughness- and final shape of themachined part, etc [7]. Austenitic steel is characterized by its:
●
●
●
●
●

Ability to work hardening
Low thermal conductivity
High toughness
Tendency to be sticky
Poor chip breaking characteristics

These are all reasons why austenitic stainless steel is hard to machine. The work hardening
is mainly caused by parts of the austenite being transformed into harder martensitic phasewhen it is subjected to high deformation rates. This can lead to machined areas with muchhigher hardness. Stainless steel has a thermal conductivity of approximately 50% of that ofcarbon steel [4,5].

5

2.5 Cemented carbide tools
Cemented carbides generally consist of two phases, a hard phase of WC sintered together
with a Co binder phase. The role of the WC particles is to provide strength and wear
resistance, while the Co binds them together and gives ductility and toughness. This gives
cemented carbide tools a combination of hardness and toughness. These properties can bevaried with different WC grain sizes and amount of binder phase. Additionally, cubic carbides
can be added, such as TiC, NbC and TaC [8,9].
To achieve further abrasion resistance and chemical inertness, coated carbide tools weredeveloped around 1970 [10]. Chemical vapour deposition (CVD) and physical vapour
deposition (PVD) are commonly used coating techniques that will enhance the wear resistanceof the carbide tool. A coating will result in an increased tool life by suppression of themechanical, chemical and thermal interactions between the workpiece material and the cutting
tool. The function of the coating is heavily dependent on its ability to improve the chip flow on
the rake face. Its surface topography, affinity to the workpiece material and resistance tooxidation are among other things important for the function of the coating [11].
Additionally, a CVD coating can be post deposition treated with top blasting. This is done to
reduce the residual stresses of the coating. As there is a difference in thermal expansion of
the CVD coating and substrate, residual stresses are created as the coating is cooled down
after deposition [12].
2.6 Wear types
Wear mechanisms, such as adhesive-, abrasive- and mechanical wear eventually lead todifferent types of wear. Tools can experience several wear types simultaneously, some ofwhich are mentioned and shortly explained below.
2.6.1 Built-up edge and smearing
Workpiece material adhering to the edge which in turn works as a new cutting edge is calledbuilt-up edge (BUE). When material is smeared over the surface of the tool creating a thinlayer, a built-up layer (BUL) is formed. The difference between BUL and BUE is that BUE
forms on the edge, displacing the edge where the cut takes place. Formation of BUE and BUL
is heavily dependent on workpiece material and occurs when machining “sticky” materials
such as stainless steel. For the adhered material to work as a BUE it needs to be harder thanthe original workpiece material, which is achieved through work hardening [11,12].
In this work BUE is defined as any material sticking to the tip of the edge after milling,
regardless of size and whether it effectively shifts location of where the cut takes place.
2.6.2 Cutting edge chippingThis is when fragments of the substrate break loose at the edge. There are several causes of
why chipping occurs, with the most probable being thermal and mechanical stress oradhesion. When workpiece material sticks to the edge it can rip off parts of the substrate as it
detaches [12,13].
2.6.3 Thermal cracking
This is usually the effect of varying temperatures of the tool during cutting. At intermittent
cutting the tool experiences varied temperatures as it enters and leaves the tool. Due to the6differences of the thermal expansion, both between the WC- and Co phase and between thesubstrate and coating. As temperature variations occur between the bulk and surface of thetool as it leaves and enters the workpiece, thermal stresses lead to the formation of cracks.
Eventually these cracks can lead to chipping or breakage of the edge. If there are any residual
tensile stresses in the coating, this can lead to formation of cracks in the coating. These cracks
are formed perpendicular to the edge, from which the name comb crack comes. A result ofcomb cracks is flaking of the coating, i.e. detaching of the coating and exposing the substrate[12,13,14].
2.7 Characterization equipment
Short description of the equipment and techniques used for characterization and analysis in
this thesis.
2.7.1 Optical microscope
Microscopes that use visible light to create a magnified image of a sample is called optical
microscopes. There are different types of optical microscopes. One of them is stereo
microscope which generally is used for low magnification of up to 100x. Due to there being
two optical paths transferring the image to the eyepieces both eyes have a slightly different
viewing angle. This makes it possible for a 3D view to be obtained [15]. Incident light isobserved, which is light reflected from the sample. The advantages of stereo microscopes are
its good working distance and depth of field. For higher magnification (40-1000x) a compound
microscope, or light optical microscope (LOM) is needed. It utilizes two lenses; the objective
and ocular. The eyepieces in LOM’s show the same image as compared to the stereo
microscope [16,17].
2.7.2 Scanning electron microscope (SEM)
The SEM uses a beam of electrons which are accelerated onto the surface of the sample. Theenergy that the electrons carry is scattered as they interact with the sample and creates
different signals that can be detected. These signals can give information of the sample
regarding surface texture, chemical composition, structure and orientation of materials making
up the sample. Commonly the signals of backscattered electrons are used to create a 2D
image of the sample [18].
2.7.3 Energy-dispersive X-ray spectroscopy (EDS)
One of the signals that are created by the electron-sample interaction is X-rays. An EDS
system has an X-ray detector which can convert the incoming X-rays into electrical voltages.
These voltages correspond to different elements and an element composition map can becreated. These usually consists of X-ray count vs energy in keV. The different elements of thesample make up different energy peaks and information of its composition is given [19].
2.7.4 Electron probe micro-analyzer (EPMA)
EPMA is an analytical tool used for non-destructive chemical analysis of small areas of solid
samples. Fundamentally the EPMA is the same instrument as the SEM but is equipped withthe means for quantitative chemical analysis. Analysis is primarily done by wavelengthdispersive X-ray spectroscopy (WDS). The sample is bombarded by an electron beam which
excites X-rays. Their wavelengths are characteristic to the elements of the sample. Analysis
can be done for regions as small as the scale of 1-2 μm diameter. Concentrations of elements
as small as 10 ppm can be detected with a precision of approximately ±1% [20,21].
7

2.7.5 Focus variation
Alicona InfiniteFocusSL is a focus variation instrument which can be used to measure form
and roughness [22]. Focus variation is a technique where an optical system with a small depthof field is combined with vertical scanning. The sample is exposed to white light which isgathered by a sensor when reflected. Due to the small depth of field only a small area isfocused. When the instrument is moved vertically along the sample, different layers of it isbeing focused. Algorithms then convert the data collected by the sensor into a true colour 3D
picture with full depth of field [23].
2.7.6 Microhardness
Microhardness testing is an indentation hardness test method. An indenter probe is being
impressed on the surface of the sample at a load of 10 N or less. The width of the indent ismeasured which indicates the hardness of the sample. Microhardness tests are being used
where the size of the sample is too small for macrohardness, as this uses a higher indenterload [24].

83. Literature study
Following is an exposition of the literature review on milling of stainless steel, formation of BUE
when machining stainless steel and the effect of the surface roughness on smearing on thetool.
3.1 BUE formation when machining stainless steel
3.1.1 Formation
BUE is formed by workpiece material successively adhering to the tool surface at the cuttingedge. This gives geometric changes to the tool and the surface of the cut material, as theplacement of the cutting edge is shifted. The material is adhered by pressure welding, whichmeans that the gradual accumulation of material takes place under high pressure. This takes
place at the stagnation zone, which is developed by the workpiece material being pressedagainst the tool. As the workpiece material must move either towards the rake- or flank face,a stagnation point is created where there is no relative movement between workpiece andtool. Thin layers of workpiece material are added one at a time, eventually forming a BUE.
The process is temperature dependent and a “favourable” temperature is required. The builtup edge consists of highly deformed workpiece material, which has become harder than theoriginal workpiece. The BUE grows until it reaches a critical size where it becomes unstable.
When the forces upon it becomes stronger than its shear strength it is sheared off. The BUE
then follows along with the chip or passes along the flank face and is deposited on themachined surface. The geometry of the cutting tool can be changed enough that the edge line
is shifted [4].
When the BUE breaks off, the cycle repeats and new layers of adhered material are formed.
The BUE consists of work hardened material and may grow so large that it can scratch theworkpiece surface. Workpiece material can fill the voids caused by chipping and thus protect
it from further imminent wear [35].
3.1.2 Affecting factors
The formation of BUE is affected by [4]:● The tool temperature, which in turn is affected by cutting speed, theoretical chip
thickness, etc.
● The adhering of the tool and workpiece material to each other.
● The shape of the cutting tool, i.e. rake angle, inclination angle and edge radius.
To avoid BUE a high enough cutting speed is needed, that exceeds a critical value. Using alarge rake angle, low feed and a smooth surface on the cutting tool will help to avoid BUE.
The cutting tool should not be able to react with the workpiece material as a metallurgicalinteraction is required to form a BUE [35].
The edge radius affects the formation of BUE as the amount of stationary material increases
with increasing radius. Increasing the edge radius will increase the deformation zone and givehigher friction [36] Friction can also be decreased by using a lubricant or using a polished rake
face. Certain types of lubricants containing additives of e.g. sulphur or chlorine can form a
non-metallic film between tool and workpiece material, which means less contact and welding
cannot take place [37].
9The reason that increased cutting speed lowers the amount of BUE is because the ease of
deformation is increased at higher temperatures. The plastic flow is higher at higher
temperatures as soft layers are created [38]. As the temperature is increased the shearing
strength of the BUE is decreased, which inhibits its formation. When using a positive rake
angle and inclination angle the adhesion of removed material is favoured to the chips insteadof the machined surface [4]. As pressure welding causes BUE it is necessary to decrease thepressure between tool and workpiece material in order to avoid its formation. An increasedrake angle will decrease the pressure at the cost of weakening the tool [37]. Mikac et. al alsomean that increased rake angle lowers the cutting forces and compressive stress on the rake
face. Increasing the clearance angle also increased the critical cutting speed for BUE
formation and could even eliminate the formation of built-up material on the flank face [36].
3.1.3 Effects on tool wear
When the BUE is sheared off it can pull some of the tool material with it. It can also lead tocrack formation, resulting in the edge breaking off.
The strength of the adhesion between the BUE and cutting tool has influence on the wear.
The tool life depends on if the adhesion is strong enough to still be attached to the cutting tool
surface when being sheared off. If the adhesion is small, it may not cause any damage to thetool or the coating. If the adhesion is greater it may still be some material adhered to the tool
when the BUE is removed. If the strength of the cutting tool or the coating attachment to it islower than the strength of adhesion it can be broken off, i.e. causing damage to the tool. Whena BUL is formed, it adheres to the crevices of the tool surface, decreasing the surface
roughness. In turn this provides additional lubrication and protects the tool as cutting forces
and temperatures are decreased [4].
3.1.4 Effects on machined surface
As the BUE can be formed along large parts of the edge it can affect the finish of the machined
surface. The geometrical shape of the cutting tool is altered which affects the tolerances ofthe machined part as the accuracy of the machining is deteriorated. This can lead to
unexpected accuracy, especially when performing finishing operations. Another consequenceis when the BUE is sheared off and passes along the clearance face, being deposited on the
newly machined surface [4,36].
3.2 Previous work
3.2.1 Milling of stainless steel
Milling of stainless steel has been investigated by several authors. Mainly the dependence of
coatings has been investigated. The presence of BUE is not a main topic discussed whenmilling. Other wear types seem to be more prominently mentioned. Adhesion in combination
with abrasion however is a wear mechanism that often is mentioned to be a cause of toolwear.
Nordin et al. performed milling tests in austenitic stainless steel. Accordingly, failure wasreached as chipping occurred with comb cracks being the limiting factor for tool life [25]. Dry
milling experiments of austenitic stainless steel grade 1Cr18Ni9Ti were carried out by Liu etal. with the aim to decrease the roughness of the machined surface and cutting forces. The
main tool failure mode was found to be chipping at the flank between the cutting edge and10

surface of the machined material. Grooves on the flank face of the tools were found whichwere said to be caused by abrasion and adhesion at higher cutting speed [27].
End milling of AISI 304 austenitic stainless steel with the aim of investigating the effect of
cutting fluids were made by Abuo-El-Hossein. It was found that for lower cutting speeds that
BUE was present and was the main cause of tool failure. This was explained as the tools failed
due to plastic deformation which was caused by the higher heat and forces. At higher cutting
speeds, or with the usage of coolant BUE could be avoided however [29].
Similar tests were made by the same author together with Yahya. When milling at different
cutting speeds, BUE was formed in the intermediate speed used and high feed, 190 m/min
and 0.075 mm/tooth respectively. BUE was absent at higher or lower speeds and feeds. The
BUE that was formed in their tests is shown in figure 3.1. It was claimed that notch wear was
the main cause of tool failure due to the work hardening effect of the workpiece material [30].

Figure 3.1. BUE formed in milling tests performed by Abuo-El-Hossein and Yahya [30].
Milling tests in the martensitic stainless steel 3Cr13Cu by Li et al. showed that for lower cutting
speeds, fatigue cracks were present. They appeared as the chip formation started to develop
serrated chips. For higher cutting speeds, thermal cracks limited tool life instead. It is argued
that the fluctuating cutting forces when serrated chips were formed is what ultimately
increased the tool wear [26].
In the workpiece material, stainless steel 3Co13CR Shao et al. performed wet milling tests. It
was found that chipping which eventually led to breakage of the edge was the limiting factor
of tool life. It was mentioned that BUE had formed on the areas where chipping had occurredand stuck to the bared substrate. In turn this protected the tool and prolonged tool life as the
BUE protected the broken area from further breakage [28].
Milling of 15–5 precipitation-hardened martensitic stainless steel was done by Braghini Junior
et al. The adhesion and abrasion was found to be the wear mechanisms that led to tool failure.
Adhesion only occurred where the coating previously had been removed, i.e. smearing was
only found directly on the substrate [31].
3.2.2 Machining with BUE formation
Several authors have previously performed turning tests where the formation of BUE wasinvestigated. Bilgin, Tekiner and Mahdavinejad all found that BUE was influenced by cutting
11speed, i.e. cutting temperature at turning of austenitic stainless steel. At low cutting speed, thepresence of BUE was higher and could be avoided at high enough cutting speed. It was foundthat increased feed rate gave higher amount of BUE. Thamizhmnaii et al, that performed dryturning tests in martensitic steel claimed that the reason of the increased amount of BUE at
low speeds is due to the cutting tool having longer contact time with the workpiece material[38,39,40,41,42].
It was shown that tests performed with a coolant gave lower amount of BUE. An explanationof this is given by Collin et al. that the thermal expansion of the chip is less which inhibits its
ability to stick to the tool [41].
EDS analysis in the BUE and found that its composition was similar to that of the workpiecematerial in an internal study at Sandvik Coromant [41]. It was concluded that the BUE
formation was not caused by any chemical reactions but rather due to mechanical work. Anyother authors are not presenting any mechanisms of forming BUE other than mechanicalsticking. Any cases where the BUE has changed composition was not found or had been
investigated. Abou-El-Hossein and Yahya found elements from the workpiece material within
the tool body, which means that diffusion had taken place. The effect this has on the tool wear
is however not mentioned [30].
Investigation on BUE formation at internally cooled drills was done by Nomani. It was foundthat adhesion was the main wear mechanism at the flank for duplex grades 2507 and 2205,
and austenitic 316L. The duplex grades suffered higher amount of BUE than the austenitic
one. Quick-stop samples were made in turning of duplex stainless steel with BUE formation.
By studying these it could be observed that ferritic α-phase had accumulated in the stagnation
zone, with the austenite flowing away from the stagnation zone. Eventually leading to the BUE
consisting of mainly ferrite. Micro-cracks were also discovered, explained as a cause of BUE
formation in multi-phased materials. Figure 3.2 show the quick-stop sample from Nomani,
where a built-up layer can be found sticking to the workpiece. It is speculated that the ferrite
build up is a triggering mechanism for the BUE. The amount of work hardening seemed to not
influence the amount of BUE as austenitic stainless steel has higher work hardening thanduplex. The same trend is found between the duplex grades as 2205 underwent higher work
hardening than 2507 but experienced less BUE. It is therefore stated that there should be
another mechanism that triggers the BUE [32].

12Figure 3.2 Quick-stop sample from Nomani [32].
Both Zhou et al. and Khan et al. performed turning tests in Inconel 718. Same conclusion was
drawn that BUE formation was higher at lower cutting speed and higher feed. Dry cutting was
found to be profitable for BUE formation. This agrees with the results when milling in stainlesssteel, with cutting speed having the main effect on BUE formation and dry cutting giving higher
amounts [33,34].
3.2.3 Effect of coating surface roughness on adhesion
Adhesion between the rake face of the tool and chips of the workpiece material in turning wasstudied by Gerth et al. A stainless steel (316L) and a carbon steel was used, where thestainless steel showed higher amount of BUL. Two different CVD-coatings were used, apolished one and an unpolished. It was shown that the polished version showed lower amountof BUL, indicating that surface roughness has a considerable effect of the amount of adheredmaterial [43]. As mentioned, Braghini Junior et al. only found workpiece material smearing on13

the tool where the coating had previously been removed [31]. This indicate the effect of coating
on adhesion when machining martensitic stainless steels.
3.2.4 Previous tests performed at Sandvik Coromant
Milling tests of had previously been performed at Sandvik Coromant where tool life was
evaluated. These tests were made within the project internally named INOX. They will
henceforth be referred to as the tool life tests. These samples were analysed to find at which
cutting parameters BUE would be present.
Three types of tests were investigated; Cutting with a lubricant, giving high variations in tool temperature which in turn lead totool failure due to comb cracking.
 Dry cutting, where the tool spindle entered the workpiece perpendicularly, and creating
cuts at different axial depths. This caused the tool to fail due to chipping of the cuttingedge.
 Dry cutting at high speed and feed rate. This caused the tool to fail due to plastic
deformation.
These tests served as a basis for the experimental tests performed in this thesis. With BUE
being found when milling with these parameters, the same were used for the tests made inthis work. This assured that formation of BUE would be possible and any testing to find properparameters could be avoided. As the inserts had been tested for tool life, the cutting edges
were in many cases too damaged to properly form any relevant examples of BUE. This may
also have caused that any potential BUE formed had been removed directly after machining.
As in general the tests in this thesis were done at shorter tool use, it made it possible toinvestigate the initial tool wear the tool life tests would have. Nonetheless, BUE was found inseveral cases, with dry cutting being predominant.

144. Methods
The tests procedures are explained with all the involved materials and equipment.
4.1 Inserts
A total of 7 cemented carbide tool types were used when performing the milling tests. All ofthem had the same geometry, equipped with two cutting edges having both positive rake- andclearance angle. The used model, R390-11T308M-MM can be seen in figure 4.1. The insert
technology varied between the inserts.
Three of the inserts had initial coating with layers of Ti(C,N)-Al2O3-TiN. Two of these grades
been treated post deposition with top blasting of varied amount. This means that the outerlayer of TiN on the rake face had mechanically been removed for these two grades. The insert
without post treatment were used as a reference, with its layer of brushed TiN. These inserts
were used to study how the change of surface influence BUE formation. This enabledinvestigation of the effect changes surfaces has on BUE formation and stainless steel.
Three of the inserts had a variant of CVD-coating with alpha-Al2O3, instead of kappa-Al2O3.
Two of these had a new coating technology with a modified layer of Al2O3. A reference insert
was used as well and which had a regular alpha-Al2O3 layer. Further details about the modified
layer cannot be stated here. The idea with modified layers was that this would lead to different
wear and potentially longer coating life.
All of the CVD-coated inserts had the same substrate which in addition to WC and Co
contained cubic carbides of TaC and MoC.
The 7th grade had a PVD-coating of AlTiN, with a substrate containing TiC and Cr3C2. As theinserts mainly vary depending on their coating, they will be referred to accordingly. The
referred names of the inserts are presented in table 4.1.
Table 4.1. Reference names of the insert grades used in this report.
Insert technology

Reference name

PVD

29400

CVD with kappa-Al2O3, brushed TiN

29401

Low top blasted CVD with kappa-Al2O3

29477

Average top blasted CVD with kappa-Al2O3

29475

CVD with alpha-Al2O3

30324

CVD with modified alpha-Al2O3 1

30320

CVD with modified alpha-Al2O3 2

30321

15

Figure 4.1. Left: top view showing the rake face. Right: side view showing the flank face.
4.2 Workpiece materials
The workpiece material consisted of three different types of stainless steel; an austenitic one(SS2343), a duplex (SS2377), and a precipitation hardened (CORRAX). The material was inform of rectangular cuboids. SS2343 had the dimensions 700x200x70 mm, and cuts weremade along the 700x200 plane. The chemical composition of the SS2343 workpiece is shownin table 4.1. The required composition of SS2377 is shown in table 4.2 and the typical chemical
analysis of CORRAX in 4.3.
Table 4.2. The required composition of SS2343 (max/min) and the actual composition, in wt%.
C

Si

Mn

P

S

Min

Cr

Ni

Mo

16.5

10.0

2.00

N

Max

0.030

0.75

2.00

0.045

0.030

18.0

13.0

2.50

0.10

Actual

0.023

0.48

1.41

0.030

0.022

17.3

11.2

2.30

0.05

Table 4.3. The required composition of SS2377 (max/min), in wt%.
C
Min
Max

0.030

Cr

Ni

Mo

N

21

4.5

2.5

0.10

23

6.5

3.5

0.20

Table 4.4. Typical composition of CORRAX, in wt%.
Typical

C

Si

Mn

Cr

Ni

Mo

Al

0.03

0.3

0.3

12.0

9.2

1.4

1.6

4.3 Experimental setup
Three variations of milling tests were performed for the austenitic stainless steel. Tests were
performed in a DGM MORI DCM 1150V vertical machining center. The tests were designed
to have three different machining temperatures; low, medium and high.
The low temperature tests were performed with a coolant present and were supposed to givea large temperature variance for the insert in every cut. Up milling was done and the test wasinterrupted after a few seconds of machining.

16

The medium temperature tests were dry tests where the spindle with the cutting insert was
introduced to the workpiece in a perpendicular angle. The tests were done with varying
amounts and lengths of the cuts for the different inserts and stainless steels. For SS2377 and
CORRAX the cuts were generally shorter than for SS2343, initially done at 1.5 mm, with some
additional samples having longer cuts up to 3 mm. This was the only milling method used forSS2377 and CORRAX.
The high temperature tests used up milling again, without any coolant. In comparison to thelow- and medium temperature tests, high cutting speed, feed rate and radial cutting depth wasused. As most of the spindle was subjected to the workpiece during machining, the insert
spent longer time in the workpiece and thereby reaching higher temperatures. Cutting wasdone in passes of 200 mm. The applied cutting methods are illustrated in figures 4.2-4.3. The
medium temperature milling method is masked in this version of the report.

Figure 4.2. Illustration of cutting method for low- and high temp. milling.

MaskedFigure 4.3. Illustration of cutting method for medium temp. milling.

17

The cutting parameters used are presented in table 4.5. Additionally, a few samples weremade with slightly changed parameters. See appendix A for the full list of all samples withrespective parameters.
Table 4.5. Cutting parameters used.
Methodvc [m/mi]fz [mm/tooth]ae [mm]ap [mm]Dc [mm]High temp

215

0.25

59.5

3

63

Medium temp

165

0.10

-

3

32

Low temp (wet) 150

0.20

15

3

25

The cutting edge of the insert were observed in a stereo microscope after every cut in order
to view if any BUE had formed. The individual tests were interrupted as a BUE had formed or
until the edge was so damaged the original cutting edge was lost.
4.4 Cross section preparation
To study the edges with the adhered material cross sections of the inserts were made. A plane
perpendicular to the cutting edge was created so the interface between the tool and the BUE
could be studied as well as the inside of the BUE. The insert was first grinded down until the
BUE was close enough, as shown in figure 4.4. The distance from the grinded edge to the
BUE was measured using a stereo microscope as well as the total distance to the furthest endof the BUE. This made it possible to know the distance required for further polishing. After the
samples had been casted in conductive bakelite, the samples with the grinded area were
initially polished with a grinding oil with 9 μm diamond polishing particles. Finer polishing
followed with 1 μm diamond particles.

Figure 4.4. Grinded insert with measurements, to know when BUE would be present during
polishing. BUE adhering to the main cutting edge with the flank facing the camera. Grinding
has been made from the left in the figure.
4.5 Quick-stop samples
Quick-stop samples were provided by Swerea Kimab, i.e. samples of the workpiece material
where the forming chip is still attached to the workpiece when machining is interrupted.
Samnac 316L, which is an austenitic steel similar to SS2343 had been machined using TCMTGC2040 tools. Nominal composition in table 4.6 [44]. The procedure to create the samples
18

involved turning where areas of the machined outer radius had been weakened in order tobreak off mid-machining, creating the still attached chip. As the workpiece was designed to let
the tool leave it as it rotated it was intermittent cutting, giving more similarities to milling eventhough turning was the used method. Dry machining at cutting speed of 144.5 mm/min, feed
rate of 0.3 mm/rev and a workpiece diameter of 120.0 mm were used [45].
Cross sections were made similarly to the insert cross sections, with the additional step ofpolishing with alumina particles in the polishing medium. This provided finer polishing andworked as etching, allowing the microstructure to be viewed. Due to the lack of equipment thepolishing optimal polishing results were not obtained. As the sample tended to becomecontaminated by the polishing cloth, polishing was interrupted. Adequate results wereobtained however. Study of any possible inclusions was thus not possible as thecontamination took form as dots on the polished surface
Nominal composition of Sanmac 316L.
C

Si

Mn

P

S

Cr

Ni

Mo

≤0.0300.3

1.8≤0.040≤0.030

17

10

2.1

4.6 Characterization methods
Several analysis methods were utilized to attain numerical results of any differences of thesamples from different milling conditions. These were performed with a focus on the BUE and
BUL formed from milling in austenitic stainless steel grade SS2343. It was focused on
revealing any differences of the characteristics of the adhered material after milling at different
temperatures.
4.6.1 Microhardness testing
Vickers hardness with 0.01 kg load, i.e. HV0.01 was performed with a KB 30 S machine fromKB Prüftechnik. The reason why this method was used was due to that higher loads caused
too large indentations. The BUE’s of the cross sections had small areas in relation to theindentions of the microhardness tests. This also meant that a limited amount of indentations
could be made in every BUE, causing a variation of indentations being made for every sample.
HV0.01 was also performed for the workpiece materials which enabled calculations of thework hardening of the BUE’s to be performed. The percent of the hardness increase wascalculated by equation 1. Where HV0 is initial hardness and HV1 is acquired hardness.
%𝐻𝐼 = (𝐻𝑉1 − 𝐻𝑉0 )/𝐻𝑉0 × 100

Eq. 1

4.6.2 EPMA
Quantitative evaluation of the present elements was performed in the EPMA. WDS analysis
was performed for three samples, one each of the low-, medium-, and high temperature millingsamples. Mapping was made for each present element, which showed where they were
present.
4.6.3 Microscopy and EDS
The cross sections of the samples with BUE were observed in both LOM. Furthermore, several
samples were analysed with EDS in conjunction with SEM. Micrographs were taken inbackscatter mode at an electron high tension (EHT) of 5 kV at varying working distances (WD).
19

4.6.4 Surface roughness
An Alicona InfiniteFocus SL was used to measure the surface roughness of the inserts. Thiswas done before and after machining. Lens magnification of 10X was used to acquire 3D
images of the cutting edges. These images were investigated using the Surface measurement
software provided by Alicona. Roughness parameters were evaluated along a profile with awidth of 10 μm and length of 2.00 mm, located along the cutting edge, as in figure 4.5.
Measurements were done 75 μm from the cutting edge. As the lowest feed used was 0.1 mm,
it was ensured that the roughness of the edge was measured where the cut would take place.
Additional measurements were done where the lowest possible roughness could be foundcloser than 75 μm from the edge. Roughness was evaluated as mean roughness (R a), whichis measured in length. The arithmetical mean of the absolute values of the deviations from themean line of the roughness profile. Figure 4.6 demonstrates how Ra is measured [51].

Figure 4.5. Surface roughness profile.

Figure 4.6. Mean roughness value, Ra [51].

205. Results and discussion
The results and discussion is divided into two parts; an observational study and acharacterization study. In the observational study the results of what can be observed after
milling is discussed. This includes the visual analysis with the use of microscopy to investigate
hypotheses A and B. In the characteristic study the results are analyses which have beenmeasured using different equipment. This regards hypothesis C.

5.1 Observational study
5.1.1 Occurrence of BUE
Each insert sample was observed in a stereo microscope and photographed after machining.
Figures 5.1-5.5 show typical results of the edges after the different machining methods. All
samples can be seen in appendix B. As can be seen from the pictures, the high temperaturemachining resulted in a different type of BUE than after the other milling methods. The BUE
covered both the curvature of the edge and the entire main cutting edge. These BUE had
similar appearance to chips. This type of BUE had been formed during several rotations of thetool. The BUE consisted of layers which each had been built up as it entered and left theworkpiece. On the low and medium temperature milled samples smaller BUE have appeared.
In these cases the BUE had been formed locally on the main cutting edge. They had strong
adhesion to the inserts and did not fall off, in contrast to the high temperature samples where
they were easily detached. On the high temperature samples, there were though a smaller,
strongly adhering BUE as well, located to the right of the larger BUE. The cross sections madehas been done at these BUE for the high temperature samples. The BUE formed when milling
SS2343 and CORRAX has similar appearance as the low- and medium temperature samples.
The frequency of BUE formed for these samples were the same as that of milling in SS2343.

Figure 5.1. High temp. milled 29477 Dp1.

Figure 5.2. Medium temp. milled 29477 Dp1.

21

Figure 5.3. Low temp. milled 30324 Dp1.

Figure 5.4. 29401 Dp1 milled in SS2377.

Figure 5.5. 29475 Dp2 milled in CORRAX.
Any difference in the amount of BUE formed on the different insert types could not be foundeither, meaning that for these tests the BUE formation was not influenced by insert technology.
BUE being present for all milling methods and workpiece materials means that the window of
cutting parameters where BUE can be found is large. BUE formation is not restricted to either
cutting temperature or workpiece material. Similar types of BUE were formed at both wet anddry cutting. This serves to prove hypothesis A, that BUE is present for different workpiecematerials as well as varied cutting parameters and conditions. This shows that indeed
austenitic stainless steel has a high span of cutting temperature where BUE is present. At hightemperature, the shape of the BUE is different though, and is located over the entirety of themain cutting edge.
There were no indications that the presence of BUE being affected by wet or dry cutting, ascompared to the literature and previous tests by Sandvik Coromant. This indicates that theformation of BUE in milling and turning is affected differently by usage of cutting fluids. As
many, or as long cuts were not done for these tests in comparison to the tool life tests. The
edges were in comparison relatively intact when cutting was interrupted, while in the previous
22tests milling was continued until tool failure. This could have an impact of the quantity ofsamples where BUE has formed.
Neither were there any differences of the occurrence of BUE comparing the workpiecematerials. BUE was shown to be formed as much and often for SS2343, SS2377 and
CORRAX. This means that for the medium temperature milling method BUE is equally present
for austenitic-, duplex-, and precipitation hardened stainless steel. To fully investigate theoccurrence of BUE for different workpiece materials a more thorough study is needed withlarger variations of cutting parameters. Moreover, SS2377 and CORRAX were only tested in
the medium temperature milling. In addition, it can be mentioned that these inserts had botha positive rake angle and clearance angle, which according to the literature would have a lower
tendency for BUE formation in comparison to negative ones.
5.1.2 Initial tool wear
It is known from the tool life tests what the eventual cause of ended tool life is when milling in
SS2343 at the different cutting conditions. The milling tests performed in this work show theinitial wear of the inserts. As the tests were discontinued after short milling times, final tool
failure was not reached. With the tests revealing initial tool wear, slight differences can befound.
5.1.2.1 Low temperature millingAt the low cutting temperature, where cutting fluid was used. The coating on the edge has
been detached at the areas surrounding the formed BUE. As any cracks has not yet
developed, this coating detachment does not occur due to comb crack formation. This may
however be the eventual cause of comb crack formation as the substrate becoming bare,undergoing higher temperature fluctuations. It appears the PVD-coated grade 29400 has
suffered less from coating detachment. The apparent difference can be seen in figures 5.65.7, with CVD-coated grade 30324 and 29400, respectively. This coating detachment may
possibly be due to BUE.

Figure 5.6. Low temp milled 30324 Dp1 with coating detachment of rake- and flank face.

23

Figure 5.7. Low temp milled 29400 Dp1 with comparatively low coating detachment.
5.1.2.2 Medium temperature milling
Coating detachment at the edge is present to some extent at medium cutting temperature.
Mainly, the edges has been damaged by minor edge line chipping. Compared to the low
cutting temperature, there has been slightly less coating detachment. The cutting edge of
29475 at medium cutting temperature is shown in figure 7.8. Smearing is visible, would preventthe tool edge from further thermal fluctuations, thus making comb crack formation less severe.

Figure 5.8. Medium temp. milled 29475 Dp1.
5.1.2.3 High temperature milling
The tool edges of the high cutting temperature samples were studied after the BUE had been
removed. Figures 5.9-5.10 shows such a case before and after the BUE was detached. Less
wear of the actual edge was detected. The edges had higher amount of smeared workpiecematerial. For several samples the insert showed to plastically deform, and thereby causing
tool failure. This was the case for the PVD-coated grade 29400, suggesting that this grade
had higher susceptibility to plastic deformation. The edge however is relatively intact. Figure5.11 shows such a case, where the BUE formed had detached before the image was taken.
Plastic deformation being the cause of tool failure was the same for the previous milling tests,
investigating tool life. The tool life is not limited due to substrate particles being ripped off byadhesion. The edge wear is not as high as for lower temperature milling. The BUE formed at
higher cutting temperature had similar appearance to those found by K.A. Abou-El-Hossein
and Z. Yahya (figure 3.1). In their test, tool failure was eventually reached by micro-chippingand cracks. These were explained to be caused by the increase of load put on the edge. Thissuggests that a similar type of wear had occurred in the previous tool life tests. However, as
these inserts failed due to plastic deformation it is reasonable that the high load andtemperature exerted on the edge was what eventually lead to tool failure.

24Figure 5.9. High temp. milled 29401 Dp1 with attached BUE.

Figure 5.10. High temp. milled 29401 Dp1 after detachment of BUE.

Figure 5.11. Plastically deformed 29400 Dp1 insert after high temperature milling.
Similar wear of the edges was found during the low and medium temperature tests. However,
it is demonstrated by the tool life tests, that failure eventually will be caused by different wear
types. This means that even though the initial wear is similar, further milling will eventuallylead to different wear. The most apparent case of this is for the high temperature milling. It canbe seen here that sample 29400 has suffered plastic deformation, while the edge line is notdamaged enough to cause failure.
5.1.2.4 Milling in SS2377 (duplex)
The amount was higher for these stainless steels than when milling SS2343. Figure 5.12 showa sample with the typical wear occurring. The length of the cuts made were shorter than forthe medium cutting temperature samples, but gave higher tool wear than milling in SS2343.
The coating detached at the edge with edge line chipping. The amount of chipping was
generally higher than when milling in the austenitic grade.

25

Figure 5.12. 29475 Dp1 after milling SS2377.
5.1.2.5 Milling in CORRAX (precipitation hardened)
The initial tool wear when milling CORRAX showed similar results as when milling SS2343.
Typical result after 1.5 mm cut is shown in figure 5.13. The amount of wear rapidly increased
when longer cuts were made however. This was evident when the cutting length wereincreased to 3 mm, as seen in figure 5.14.

Figure 5.13. 29477 Dp1 after a 1.5 mm cut in CORRAX.

Figure 5.14. 29477 Dp2 after a 3 mm cut in CORRAX.
5.1.2.6 Effect of top blasting post treatment
The effect of top blasting could clearest be seen for the medium temperature tests. Figures
5.15-5.16 show the reference insert, 29401 and its corresponding top blasted version 29477,
after milling at medium temperature. The coating of the insert without top blasting wasobserved to have suffered more coating detachment on the edge. Since 29401 has anadditional layer of TiN, it is however not seen whether it is mainly this layer that has been
detached. From figure 5.15 it cannot be seen if the two layers of coating underneath had thesame amount of detachment. This was further investigated in 5.1.3.3, where the wear of
coatings were studied for cross sections of the inserts. Any difference in the amount of BUE
formation cannot be found. Thus, the top blasting post treatment does not influence the ability
to form BUE.
26

Figure 5.15. 29401 Dp1 (no top blasting) after medium temp. milling.

Figure 5.16. 29477 Dp1 (Low top blasting) after medium temp. milling.
5.1.2.7 Effect of modified Al2O3-coating
The ability to form BUE was not found to be affected by using modified Al2O3-coating. Initial
tool wear was also observed to be similar for both the modified versions and their reference.
Both ability to form BUE and initial tool wear was found to be similar to those of the remaining
CVD-coated versions. Figures 5.17-5.19 Show the modified inserts and their reference.

Figure 5.17. 30324 Dp1 (single-layered Al2O3-coating) after medium temp. milling.

Figure 5.18. 30320 Dp1 (modified Al2O3-coating) after medium temp. milling.

27

Figure 5.19. 30321 Dp1 (modified Al2O3-coating) after medium temp. milling.
5.1.3 Cross sections
Cross sections of the Inserts were done for several samples. This allowed investigation of boththe BUE and the tool wear occurring underneath.
5.1.3.1 Tool wear
It was previously stated that the initial tool wear at low- and medium cutting temp was similar.
When observing the cross sections, this is the case as well. The coating at the tip of the edge
has been worn off with workpiece material smeared on the rake face. The appearance of the
BUE was similar as well for these two milling conditions. This suggests that a similar process
has taken place during the formation of the BUE. The appearance of the BUE formed at hightemperature had a different appearance where the BUE was formed over the entirety of theedge. These BUE also had serrated appearance, just in a larger scale. Cross sections of thesesamples showed that the edge had been worn in a similar matter as during the other milling
conditions. The top layer of the coating has been worn off with workpiece material sticking to
the Ti(C,N) layer.
5.1.3.2 Appearance of BUE
As can be seen from the cross section images acquired by LOM, the material is adhered at
different layers. The BUE is mainly adhering to the tool at the tip of the edge, while smearedmaterial is located at the rake face of the edge. The BUE that is formed is shown to overhang
the rake face while it is sticking to the edge tip. This is clearer when the BUE has a shapesimilar to that of a serrated chip. These serrated types of BUE are found both at low- andmedium temperature milling. This implies that the BUE is formed during an interval where it isbuilt up periodically. Cross sections of one sample each from the different milling temperature
tests when milling SS2343 are shown in figure 5.20-5.22.

28

Figure 5.20. Low temp. milled 30324 Dp1.

Figure 5.21. Medium temp. milled 29477 Dp1.

29

Figure 5.22. High temp. milled 30320 Dp1.
5.1.3.3 Wear of coating
Similar coating wear can be observed for the CVD-coated inserts. The top layer of Al2O3 isinitially worn off. The cross sections show that it is mainly the top layer of the coating which
has been detached. Adhesion mainly takes place at the substrate or the Ti(C,N) layer in the
majority of the samples. When investigating the effect of the modified Al2O3, any evidence
that the coating would be worn differently compared to the other grades has not beenvisualized by the cross sections made. This layer of the coatings was rapidly worn off,
depleting its effect. Partial removal of the coating layer is found for other insert technologies
as well, such as top blasted 29475 in figure 5.23. This type of coating wear seems to beoccurring arbitrarily among the samples, showing that any unique effect of modified coating
cannot be found.
The effect of top blasting was further studied in the cross sections. Figure 5.24 shows the
cross section of 29401 after medium temperature milling. It can be seen that the coating has
suffered similar wear as for the top blasted inserts, with the Ti(C,N) layer of the coating
remaining mostly intact. Instead the top layer of TiN has mainly been worn off. This meansthat top blasting did not affect initial tool wear, as previously suggested.
BUE was also found to be adhering to the coating. Figure 5.25 shows that BUE formation
could not be prevented, even when the coating remains intact. The top blasted grades, 29475
and 29477 suffers similar wear and it cannot be concluded that top blasting has any effect onadhesion.

30

Figure 5.23. Medium temp. milled 29475 Dp1, with partly removed top layer of coating.

Figure 5.24. Tool wear on 29401, without top blasting. Similar coating wear as the top blasted
inserts

31

Figure 5.25. BUE formed at medium temp. milled 30320 Dp1
As these tests only investigated BUE formed at initial milling, the effect of the modified coatings
can only be concluded in this regard. However, as there was a limited amount of test samples,a more extensive investigation could give results with higher consistency. This could properly
show any potential difference, but for the test samples made here, any difference cannot befound.
5.1.3.4 Cross sections of tool life samples
As several inserts from the tool life tests were also investigated, samples of these had crosssections made. These cross sections were prepared the same way as those of the newer test
samples. The edges underneath these BUE showed to have suffered the same wear as thenewer milling samples. As the BUE in these cases were found at the locations where tool
failure had not occurred, these cross sections were made where the edges were still relatively
intact. When the cross sections from the tool life tests and initial wear tests were compared,
any difference could be found between the adhered material and the tool wear.
Figures 5.26-5.28 show cross sections made from tool life samples. These images show theinsert edges and their corresponding cross sections. The BUE formed during different milling
conditions are showed. What can be seen is that the inserts have reached failure due todifferent wear types. The BUE on the other hand look similar to each other. All three of themadheres to the surface where the coating has been removed and stretches over the surface
at the rake face. The substrate has been removed slightly where the BUE have adhered andsmearing on the rake face is present.

32

Figure 5.26. High temperature milled 29400. (U8968 Dp3)

Figure 5.27. Medium temperature milled 29475. (U8932 569-415 SG AV TB Dp1)
33

Figure 5.28. Low temperature milled 29400. (U8897 190-0.15)
5.1.3.5 SEM analysis
SEM images were obtained for three different samples, one from each milling cutting
temperature. All images can be found in appendix D. What needs to be noted is that thesesamples show artefacts from the sample preparation. As the adhering material is softer than
the substrate, grooves from the polishing is visible, as the polishing method used is actuallymeant for cemented carbides and not stainless steel. Additionally, the samples were left barein an ultrasonic cleaning bath, which seemed to have some etching effect. This can be seenby the strange appearance of the BUE surface. Further polishing was however not attemptedwith the fear of polishing too much, removing the area to be studied.
SEM images showed that the WC- grains had been fragmented where the substrate had been
exposed. With the fragments located in the border between substrate and BUE it can be notedthat strong adhesion had taken place. After the WC-grains had been cracked and fragmented
they were ripped off by the adhering BUE providing attrition of the edge and resulting in tool
wear. Figures 5.29-5.31 show that this takes place for all three milling methods.

34

Figure 5.29. Low temp. milled 30324 Dp1. Fragments of the WC-grains are seen entering the
BUE.

Figure 5.30. Medium temp. Milled 29477 Dp1. Fragments of WC-grains has moved into the
BUE.
35

Figure 5.31. High temp. milled 29400 (U8968 Dp3). Fragments of WC-grains has moved into
the BUE.
It is evident that the WC-grains has been shattered during all three milling methods used.
Smaller fragments of WC-grains are found along the interface between BUE and substrate.
The shattered grains are found where the coating has been worn off, baring the substrate.
Cracked grains can also be seen in fig. 5.32. These appear below the coating which has partly
been worn off.
The interface of coating and BUE is shown in figure 5.33 where pieces of the coating is
introduced to the adhering material at the interface. As both particles of the coatings andsubstrates are joined with the BUE it can be assumed that the adhesion is strong and causes
both wear of the coatings and substrate.

36

Figure 5.32. Medium temp. milled 29477 Dp1.

Figure 5.33. BUE adhering to coating at low temp. milled 30324 Dp2.

37

What the three samples have in common is the occurrence of black spots which appears as
inclusions. These appear to be spread out randomly in the BUE. Any notable difference in thenumber of spots cannot be found between the samples. They are present for the different
insert grades and appear both where the coating has been worn off and where it is still intact.
Their presence is independent of milling method, location and insert technology. Due to theshape of the spots it is speculated that they may be a result of sample preparation. They show
to have angular shape and any signs of deformation cannot be seen. Were they inclusions, itwould be likely that they would have deformed during the formation of BUE.
As seen in figure 5.34 a new phase has been created between the substrate and the BUE at
29400 after milling at high temperature. This is the only apparent sample where thisphenomenon was found. Observing the image, it appears to be stainless steel interspersed in
between as the shade of the BUE can be seen among the darker one. The inclusions foundin the BUE can also be found within this phase.

Figure 5.34. High temp. milled 29400 (U8968 Dp3).
5.1.4 Quick-stop samples
The quick-stop samples are presented in figures 5.35-5.37. The austenitic microstructure canbe seen, as well as the flow patterns of the deformed material. Any BUE which had loosened
from the tool edge and adhered to the forming chip was not found. Flow patterns at the tip ofthe cutting edge, where the chip is being formed show that there are stagnation zones. These
are necessary to form BUE as the material will not stick to the tool edge if it is instead flowing
away. The chip that is forming is being serrated, showing that the shear strain is alternating.
It is believed that the chips from the milling tests were formed similarly. These were also
serrated and machining was similar in terms of material and method. There is nothing
indicating that serrated chips and BUE has any causal relationship, they are however often
38both present when machining similar materials such as stainless steel and titanium. A
deformed layer at the newly machined surface is visible, with the original microstructure foundseveral tens of μm underneath. This demonstrates the work hardening of the material andshows its effect in the depth of the surface. Note that figure 5.35 is from an earlier stage in thepolishing, where less contamination had taken place. The microstructure is therefore more
visible, than after further polishing.
When comparing to the quick-stop sample of Nomani (figure 3.2) a similar flow pattern can be
seen. At the stagnation zone, the flow pattern has a finer structure. As these quick-stopsamples had similar appearance it is not unlikely that BUE formation was present whencreating the quick-stop sample for this thesis. The likelihood of BUE formation is increased
when comparing the cutting parameters used for these quick stop samples and those used by[41]. They made turning tests in the same workpiece material, Sanmac 316L. A lower cutting
speed of 120 m/min and higher feed rate of 0.3 mm/rev, were used in the quick stop sample
compared to turning in [41]. It is likely that BUE was formed during its creation, as the literatureshows that BUE formation is higher at lower cutting speed and higher feed rate, which are thecases for the quick-stop sample.

Figure 5.35. Cross section of quick-stop sample.

39

Figure 5.36. Cross section of quick-stop sample.

Figure 5.37. Cross section of quick-stop sample.

40

5.2 Characterization study
These are the results and discussion from the characterization analyses used for investigationof the possible differences between the BUE formed for different milling conditions.
5.2.1 Microhardness tests
Microhardness tests were performed with varied amount of indentations in every sample due
to limited area of each BUE. The results are shown in table 5.1, where an average for every
sample was calculated. See appendix F for complete results of the individual indents, where
the lines coloured yellow are representing tests that did not give any good results. Examplesof these are where the indentation was uneven or where the indenter failed to penetrate thesample correctly. These individual results are therefore disregarded. Unfortunately, any
results cannot be presented for the high temperature milling samples as any successful tests
were never achieved. HV0.01 tests were also performed in the unmachined workpiecematerial SS2343, also presented in table 5.1 and appendix F. According to the material
specification the hardness varied between 78-95 HRB, which corresponds to 144-218 HV [47].
The result from the HV 0.01 test shows a similar value, which shows that credible values could
be reached using this method. Hardness tests of SS2377 and CORRAX had already been
performed at Sandvik Coromant of 215 HB and 349 HB respectively [45]. This corresponds to
Vickers hardnesses of approximately 225 and 370 respectively [46,47]. The averagemeasured hardnesses of the BUE formed when milling SS2377 and CORRAX is shown intable 5.2. The complete results from the measurements can be seen in appendix F.
Table 5.1. Average Vickers hardness of the BUE when milling SS2343.
Milling
Grade
Numberof Average
Methodconditionindents
hardness

Hardnessincrease (%)

None

SS23439209

HV 0.01-

Low temp.

29400

3

436

HV 0.01

109

Low temp.

30320

1

431

HV 0.01

106

Low temp.

30321

2

373

HV 0.01

78

Low temp.

30324

1

437

HV 0.01

109

Medium temp. 29475

5422

HV 0.01

102

Medium temp. 30320

3410

HV 0.01

96

Medium temp. 30324

4375

HV 0.01

79409

HV 0.01

95

Table 5.2. Average values of the Vickers hardness measurements in BUE when milling
SS2377 and CORRAX.
Workpiece material Average hardness

MethodHardness increase (%)

SS2377441

HV 0.0196

CORRAX401

HV 0.01

8.4

Any variation in the hardness results between the different milling conditions cannot be foundas similar values are obtained. The hardness of the deformed material of the BUEs are
considerably higher than that of the original workpiece material. The hardness has in several
41

cases doubled in comparison. This increase in hardness suggests that something has
happened during deformation of the material. Either normal work hardening has occurred
where the dislocations in the atomic lattice has tangled and restricted movement, or thematerial has undergone phase transformation, e.g. forming a harder, martensitic phase. Any
differences between the milling conditions cannot be found, which does not suggest any
difference in the BUE that have formed.
The measured hardness for CORRAX shows that it had considerably lower work hardening
than the other workpiece materials. This was expected as the precipitation hardened steel had
a higher initial hardness of approximately 370 HV. With the margin of error being considered
big for these measurements it is not possible to say if any actual work hardening has takenplace, as a result of 8.4% hardness increase was achieved. The increase of the hardness
regarding the BUE of SS2377 is higher, with a total average increase of 96%, while that of
SS2343 was 95%. It is unlikely that SS2343 had experienced higher work hardening thanSS2343 as the body-centered-cubic (BCC) structure of the ferrite phase does not have as
high work hardening ability as the face-centered-cubic (FCC) structure of austenite.
Considering Nomani’s claim, that BUE when machining Duplex stainless steel mainly consistof ferrite also indicate the inaccuracy of these measurements.
For the different milling conditions the hardness of the BUE has measurements of similarvalues. The results do not show that the BUE formed at different cutting parameters orworkpiece materials has any differences in regards of hardness. Even though the initialhardness of the workpiece materials differed the final hardness of the BUE was found to bearound 400 HV with SS2377 being slightly higher. This implies that the work hardening of thematerial does not solely affect the BUE, when disregarding possible inaccuracies of themeasurements. Similar hardness increase, i.e. work hardening was found for austenitic- andduplex stainless steel, while that of CORRAX was less than a tenth of those. For the milling
conditions used, the BUE formation does not depend on additional hardness of the workpiecematerial or its work hardening. The final hardness however is found to have similar values
regardless of cutting method or workpiece material. This agrees with the findings of Nomani,that the ability to form BUE does not mainly depend on the work hardening properties of amaterial.
The credibility of the results is reduced as several requirements has not been fulfilledaccording to the ISO 6507 standard. This is concerning the BUE hardness tests and not of theworkpiece. A distance equal or greater than 3 times the indentation diameter is standard. A
specimen thickness of 1.5 times the indentation diameter [48]. These requirements were notpossible to reach due to the limited cross section area. However, the results are trusted
enough to show that an increase of hardness has been achieved, as such large deviation fromthe workpiece material is found. Their numerical credibility is nevertheless low.
5.2.2 EPMA
The results from the quantitative WDS tests in the EPMA can be seen in figures 5.38-5.41.
These results do not show any values of the actual compositions, but rather how theoccurrence of elements vary at different locations of the sample. This means that the maps ofthe elements cannot be compared to one another as the colour coding is based on eachelement where red is the highest amount present and blue is the lowest.
42

Figure 5.38 shows the element mapping of the BUE on high temperature machined 29400. A
layer has formed between the tool edge and the BUE. This can be seen clearer in figure 5.39.
From the element mapping, it is evident that it has of a chromium amount which is higher thanthat of the BUE. It is also evident that oxygen is present in this layer as well as manganese.
This indicates that a chemical reaction has occurred when SS2343 was machined at highcutting temp and a compound enriched of Cr, O and Mn has been formed. It can be an oxideof Cr and Mn. According to the Ellingham diagram, figure 5.42, oxidation of Cr and Mn takes
place around the same temperatures and Gibbs free energy change (ΔG). The other elementsof the workpiece material are not thermodynamically oxidized at the same ease, or have lower
weight percent. This would explain why any nickel oxide or silicon oxide is not detected. The
Ellingham diagram can also give an explanation why this Cr-Mn-O enriched layer only is foundat the high cutting temp, as the free energy of formation of the oxides is increased at higher
temperature.
Same analyses were done for low temperature milled 30324 Dp1 and medium temperaturemilled 29477 Dp1. Figures 5.40 and 5.41 respectively. Any similar layer in the BUE was notfound however.

Figure 5.38. WDS element mapping of high temp. milled 29400. (U8968 Dp3)

43

Figure 5.39. EPMA image of high temp. milled 29400. (U8968 Dp3)

Figure 5.40. WDS element mapping of low temp. milled 30324 Dp2.

44

Figure 5.41. WDS element mapping of medium temp. milled 29477 Dp1.

Figure 5.42. Ellingham diagram for several metals [49].

45

5.2.3 EDS
The cross section samples were further studied in SEM with EDS analysis being performed.
It should be noted that the compositions that are presented should not be taken as precise
results, as these are merely quantitative measurements rather than qualitative. For highaccuracy WDS measurements are needed. The results here serve by being compared to eachother.
5.2.3.1 Point analyses
Electron beam current of 20 kV at a working distance of 12 mm were used. As expected, the
EDS analysis of the SS2343 workpiece material showed to give similar results as the given
composition. This is regarding the heavier elements present, i.e. the metals. The measured
composition is presented in table 5.3, which is the average values from 3 spectra. Deviations
from the specification of the workpiece material could be found. The amount of carbon wasabove 5 wt%, in comparison to 0.023 as given. This could be explained by the polishing agent
consisting of diamonds, which had contaminated the sample and thereby increasing its carbon
content. It is a similar value to that from the EDS analysis of Collin et al [41]. Additionally, lightelements which have an atomic number below that of Na are hard to detect. Consequently,
these results cannot be seen as credible as those for the heavier elements. Regarding Al, Ti,
Co and W, their presence is unlikely as their peaks in the spectra are either not visible or the
result of interfering peaks. This is shown in figure 5.43 which displays one of the spectra
acquired. The peaks found around 7.1 and 7.5 are actually corresponding to iron and nickel,
respectively [50].
Table 5.3. Average composition in wt% from EDS measurements of unmachined SS2343.
C

Si

Mn

Cr

Ni

Mo

O

Al

Ti

Co

W

6.97

0.47

1.41

16.10

10.47

2.07

0.36

0.00

0.01

0.55

0.14

Figure 5.43. EDS spectrum of SS2343 workpiece.
The same measurements were done for the samples of grades with different milling
conditions. These were grades which had machined the austenitic SS2343. Electron imagesof the analysed areas are shown in figures 5.45-5.47. Point analyses were made to measure
the composition of the BUE in order to compare between the samples. As noted earlier there
could be seen that material had adhered in different layers. These layers were studied toinvestigate if they showed to have varying compositions. This was done with line scans, where
46the change of the element count would reveal the presence of any deviations in composition.
The values from the point analyses of the compositions are presented in table 5.4.

Figure 5.44. Electron image of low temp. milled 30321 Dp1.

Figure 5.45. Electron image of medium temp. milled 30320 Dp1.

47

Figures 5.46, 5.47. Electron image of high temp. milled 30320 Dp1. Same edge at two different
locations.

48

Table 5.4. Measured compositions from the EDS point analyses.
Grade, milling temperature, spectrum
30321 Dp1, low
wt%

3

4

5

30320 Dp1,
medium
1
2

C

7.44

9.7

6.27

3.72

4.34

11

13.02 11.56 10.99 12.41 20.36 20.35

Si

0.5

0.49

0.69

0.44

0.53

0.45

0.42

0.39

Mn

1.33

1.38

1.34

1.39

1.30

1.41

1.35

1.18

Cr

15.73 15.81 15.77 17.49 17.25 15.11 15.1

14.56 14.43 14.36 12.27 12.63

Ni

10.59 9.85

10.34 10.47 10.73 9.66

9.03

9.24

9.68

9.51

8.56

8.74

Mo

2.13

2.18

1.96

1.94

1.85

2.05

2.09

1.73

1.74

O

0.71

0.13

0.6

1.18

1.25

1.88

1.74

Al

0.04

0

0.06

0.06

0.04

0.07

0.02

0.07

0.01

0.03

0.85

0.14

0.09

0

0.53

0.43

0.69

0.66

0.58

0.65

0.48

0.25

0.12

1.85

0.59

0.71

2.7

1.43

2.16

Ti

2.09

0.2

Co
W

0.7

0.58

2.16

29475 Dp1, medium 30320 Dp1, high
13

14

15

9

1.32

10

1.3

11

12

0.45

0.39

1.24

1.23

The sample milled at low temperature had results similar to SS2343. The measurements takenfrom the different analysis points showed similar values. This means that the two different
layers of the adhered material does not have any different compositions, i.e. the BUE does
not vary by time of formation here. The medium temperature milled samples gave similar
results, with the addition of Ti being present. The C-content had higher values than the lowtemperature one. The result of this is the concentration of the other elements showing slightly
lower values.
By comparing the results between the samples, milling with higher temperature shows that Ti
is present. According to the results, higher temperature generally shows to give the highest Ti
content. By studying the spectra shown in figures 5.48-5.50 it is shown that a clear peak ispresent for the when temperature has been higher during milling. The Y-axis represent the
number of X-rays detected, or counts, and the X-axis shows their energy level. The wt% of Ti
is varying between different points, indicating that there is a locational dependence. theamount of O measured is significantly higher for this sample. This ties together with the resultsfrom the EPMA, which showed that O was present and especially in the different layer formedat the BUE of high temperature milled 29400. To further demonstrate that Ti is present for thehigher milling temperatures figures 5.42-5.44 show EDS spectra of the samples at different
milling temperatures. Corresponding composition can be seen in table 5.4. The Ti peaks areclearly visible here, evincing its presence.

49

Figure 5.48. EDS spectrum 3 from low temp. milled 30321 Dp1.

Figure 5.49. EDS spectrum 1 from medium temp. milled 30320 Dp1.

Figure 5.50. EDS spectrum 9 from high temp. milled 30320 Dp1.
5.2.3.2 Line scans
Line scans enabled comparison between the multiple layers of adhered material. The number
counts from each element is plotted against the distance of the line in figure 5.51-5.53. Eachline scan plotted corresponds to the drawn lines seen in figures 5.45-5.47 where the end of50

the line marked with a dot represent the start of the line scan. From the plotted line data it canbe seen that the number of counts have equal values throughout the distance on the line, withthe exception of line data 3 in figure 5.51. The reason for this can be seen in figure 5.44 where
there is a disruption of adhered material. The count values eventually reach the same values
on each side of the disruption showing that the value count is the same for both layers ofadhered material.

Figure 5.51. Line data of low temp. milled 30321 Dp1.

Figure 5.52. Line data of medium temp. milled 30320 Dp1.

51

Figure 5.53. Line data of high temp. milled 30320 Dp1.
5.2.3.3 Additional EDS analysis
More thorough EDS analyses were done for the sample where it was shown that a new phase
had been created. This was PVD-coated 29400 (U8968 Dp3) which had undergone hightemperature milling. Notably, this is one of the samples from the tool life tests. Figure 5.54
shows a map spectrum of the present elements in the BUE. What is shown in the figure is the
BUE on the left side of the substrate with the Cr-O-Mn enriched layer in between as seen in
the EPMA. Figure 5.54 shows that this area contains O and has slightly higher amounts of Cr
than the BUE. Nothing can be noted here in regards to the amount of Mn, as a higher amountnot is detected compared to the BUE material. The amount of Ti is also shown to be slightly
higher in the new phase.
This shows that the WDS in the EPMA and the EDS agrees on Cr and O being present in this
newly formed phase. The insert is subjected to the workpiece for a longer time at the hightemperature milling process. As this sample is one of those from the tool life tests it would
mean that it had experienced longer machining time as well as it was not immediatelyinterrupted as soon as BUE was discovered. The measured composition from point analyses
is shown in table 5.5.

52

Figure 5.54. Element spectrum mapping of BUE after high temperature milling with PVDcoated 29400 (U8968 Dp3).
Table 5.5. Wt% of the elements present in BUE on high temperature milled 29400 (U8968
Dp3) from different spectrums (Sp) and sites (s) of the same sample.
Fe

Ti

C

17.5 10.4 6.6

5.7

Sp4, s1 56.1 18.8 10.4 5.7

5.1

Sp11, s2 55.7 17.5 10.7 6.9

5

Sp3, s1 56

Cr

Ni

Mo

O

W

S

Si

Al

N

Co

2.2

0.8

0.5

0.3

0

0

0

1.9

1.2

0.5

0.3

0

0

0

1.9

1.7

0.3

0.3

0.1

From the weight percentages presented in table 5.5 several similarities from the workpiecematerial could be found. The most prominent elements in addition to Fe; Cr and Ni areapproximately the same amount as the unmachined SS2343. The same is the case for Mo,
except for spectrum 3, site 1, where it was not detected. Most probable reason is that Mo was53unticked when choosing elements to include in the software. Beside from that, similar
compositions have been found for the different point analyses.
The composition was similar to the measured value of the workpiece in EDS. Several wt% of
Ti is shown to be present. These values were higher than those from previous results listed intable 5.4. Reasons for this could be that different currents of the electron beam were used, 5kV here and 20 kV in the other tests. Different working distances were used as well, with 8
mm and 12 mm respectively. However, this points towards the phenomenon of Ti entering the
BUE as previously noticed. The only sources for Ti is the coating (TiAlN) and the substrate(TiC). Table 5.6 shows the composition of the PVD-coating as measured in EDS. However,as Ti is found in the BUE formed on the CVD coated insert, this takes place even when thesubstrate does not contain Ti. This suggests that diffusion has occurred where titanium has
moved into the machined steel from the coating. Likewise, this may be the case of the Cr-richsegment, as this substrate contains Cr in form of Cr3C2. This segment is however spread overboth the coating and the substrate on the edge. It would be unlikely that Cr had diffusedthrough the coating. The origin of Cr in this segment is thereby most likely the stainless steel.
The occurrence of Mn in this segment as noted in the measurements in EPMA also points
towards its origin being the workpiece material.
Table 5.6. Wt% of the elements of the PVD-coating of 29400 (U8968 Dp3) after hightemperature milling.
Ti

Al

N

C

O

Sb

W

Co

Cr

Sp5, s1 35.2 32.2 25.0 5.9

0.8

0.5

0.4

0.0

0.0

Sp6, s1 41

29.8 22.4 4.7

0.8

1

0.2

0.1

Sp12, s2 43.3 29.1 21.3 4.2

0.9

0.2

0

0.1

In the observational study, it was noted that the BUE contained black spots, similar toinclusions. The results of point analysis of these are presented in table 5.7. As can be seen,
the measurements show varied results. Several resemblances can be found between themeasured spectra however. The spots contain Ti some extent, having higher values than
measured for the bulk of the BUE. Since the coating is the only source for Ti, this must be its
origin. Both the PVD-coating and the inner layer of the CVD-coatings contain Ti. Al and N also
have higher amounts than the bulk, which the coating also contain. These spots are therefore
likely the result of coating fragments entering the BUE. These fragments have either enteredduring machining or the sample preparation when polishing the cross sections.
Table 5.7. Point analyses of black spots
Fe

Cr

Ni

O

W

Si

Al

N

Co

Sp1, s1 40.1 14.3 6.5

15.7 16.1 2.5

0.4

0.3

3

1.2

0

Sp2, s1 30.3 10.5 5.4

28.5 6.5

0.3

0.3

9.4

5.9

0.1

Sp9, s2 35

16.7 22.2 3

0

3

0.2

0

9.2

1.4

0

0

0

14.1 5.8

Sp21, s4 48.2 18.4 8.9

Ti

C

2.9

12.5 1.3

What these results indicate is that at high machining temperature the composition of the BUE
can be varied from the workpiece material when machining SS2343. At the low and medium
54temperature milled samples the BUE has measured values of the composition similar to theworkpiece material. The Ti-content is increased in a few cases at medium temperature,
meaning that there is a slight difference. When machining at the high temperature however
this difference becomes more emphasized. As no more drastic changes can be found between
the workpiece and BUE there is no reasoning that its formation is dependent on any othermechanisms than adhesion. This agrees with the findings of M. Collin et al. at turning ofaustenitic stainless steel. Any deviations from the workpiece material was not found there
either, concluding that any chemical reactions were not the main cause of BUE formation.
5.2.4 Surface roughness
The values from the surface measurement tests of the unused inserts are presented in table
5.8. These measurements show that there is a slight variation of the surface roughness of thedifferent inserts. The top blasted versions show to have lower surface roughness incomparison to the untreated reference insert. This suggests that more workpiece material will
adhere to these surfaces, as described by J. Gerth et al. The surfaces of the modified alphaAl2O3 coated inserts were shown to have a slightly lower surface roughness in comparison tothe other inserts.
The used inserts were investigated in the same manner as the unused ones, with themeasurement taken place at the surface where smearing had occurred. These results arelisted in table 5.9. The profile used for these measurements had to be modified in several
cases as segments with BUE would give inaccurate results. It was found that the smearedmaterial had varied effect on the surface roughness. In several cases the smeared areas hadsmoother surface than the original insert, while in other cases it was the opposite.
Measurements taken close to the edge generally had lower roughness than those further fromthe edge. Generally, milling in duplex and CORRAX gave higher roughness of the rake face.
This could be the effect of less smearing with the measurements taking place on the wornrake without as much smooth workpiece material.
Table 5.8. Surface roughness (Ra) for the inserts before milling.
Measurement specification

InsertSurface roughness, Ra [nm]75 μm from edge

29400

546

Lowest found value
75 μm from edge

494
29401

395

Lowest found value
75 μm from edge

281
29475

555

Lowest found value
75 μm from edge

407
29477

441

Lowest found value
75 μm from edge

379
30324

523

Lowest found value
75 μm from edge

408
30320

416

Lowest found value
75 μm from edge

303
30321

346

Lowest found value

324
55

The surface of the PVD-coated insert 29400 was measured to be slightly higher than most of
the other inserts. After machining however, it was found to generally have smoother surface
than the others. This can be the effect of even smearing of the rake face, or the fact that thethinner PVD coating was more uniformly worn off in comparison to the CVD-coatings. It wasnoted that mainly the top layer of the CVD-coatings was detached. Uneven detachment would
lead to higher roughness measured.
Table 5.9. Surface roughness (Ra) for the inserts after milling.
Milling condition

InsertSurface roughness, Ra [nm]Low temp.

29400

331

Low temp.

29401

349

Low temp.

29475

376

Medium temp.

29400

440

Medium temp.

29400

425

Medium temp.

29401

478

Medium temp.

30324

403

High temp.

29400

447

High temp.

29401

465

High temp.

29475

598

High temp.

29477

353

High temp.

30321

Duplex

29401

1371

Duplex29477

530

Duplex30320, close to edge

507

Duplex30320, far from edge

427

Duplex30321

529

Duplex30324, close to edge

324

Duplex30324, far from edge

513

CORRAX

29400, close to edge

295

CORRAX

29400, far from edge

382

CORRAX

29401

1662

CORRAX

29475

578

CORRAX

29477

385

CORRAX

30320, close to edge

369

CORRAX

30320, far from edge

787

CORRAX

30321, close to edge

233

CORRAX

30321, far from edge

637

CORRAX

30324

395

56

6. Conclusions
BUE was formed at all cutting conditions and workpiece materials. Cutting at low- and medium
temperatures gave BUE with similar appearance, while high temperature gave BUE which
covered the entire main cutting edge but was more easily removed. This showed that BUE
was present in a wide range of cutting temperatures and workpiece material during milling.
Cross sections of the inserts with BUE showed that the BUE had similar appearance
regardless of cutting conditions. Smearing had taken place on the rake face, covering thecoatings. BUE stuck to the edge spanning over the rake face and in several cases covered
the smearing without sticking to it, showing that the further adhesion was prevented on therake faceSamples where the substrate was exposed showed that the WC grains were shattered.
Adhesion was showed as both coating and substrate had detached and entered the BUE.
Previous tests showed that final tool failure however was reached due to different wear types.
The tools were worn differently even though the adhesion was similar.
Different insert grades were used where top blasted versions and modified versions werecompared to reference grades. The reference insert for the top blasted versions showed tohave slightly more coating detachment. Cross sections did not show any dissimilarities of the
BUE formation for these grades, evincing that top blasting and modified Al2O3 of coatings did
not have any noticed marked effect on the wear and adhesion for the performed tests.
EDS analysis of the adhered SS2343 showed that at different cutting temperatures the only
deviation from the workpiece material was that titanium was found at medium- and high cutting
speeds. With the only source of Ti being the coating indicate that at higher temperatures it
diffuses into the adhering material. This phenomenon was found for both the PVD- and CVDcoated grades used. A section of an additional phase was found for a high temperature milled
sample. EDS and WDS mapping showed that it had an elevated amount of Cr and O, which
could mean oxidation of Cr originating from the workpiece.
Microhardness tests of the BUE showed that work hardening had taken place. The BUE had
hardnesses measured to about twice that of SS2343 and SS2377. The hardnesses measured
were similar for all BUE samples regardless of workpiece material and cutting temperature.
Thus, the BUE formed had similar properties for all cases.
Surface roughness measurements did not show that the small differences measured had any
evident effect on amount of adhesion. Smearing was found to affect the roughness irregularity,
samples showing that it both could increase and decrease roughness.
Additionally, quick-stop samples of Sanmac 316L were investigated. No BUE sticking to thechip was found, which would be the case if a BUE had newly been disengaged from the cuttingedge. Flow pattern including a stagnation zone was visible, which is required to form a BUE.
Comparing the cutting parameters to other tests in the literature suggested that BUE would bepresent during the creation of the Quick-stop sample.

57

7. Recommendations for future work
As this work had a broad focus regarding the formation of BUE, several recommendations canbe made for future work in the area.
Microhardness tests were seen to not have been the most efficient method to measure thehardness of BUE. This was due to the impressions being too large to sufficiently ensure proper
measurement. Instead Nanohardness should be used, ensuring that proper distances can bemade between the indents, giving more reliable results.
A more thorough analysis in EPMA would more clearly show the differences in composition
between the samples, as EDS is less accurate.
When comparing the effect of different insert technologies, tests with a smaller focus should
be made. This would mean that higher focus would be put on a specific technology and ahigher number of samples could be made. A higher number of tests would provide a morereliable result, deleting the risk of inconsistencies.
Analyses of the microstructure of the BUE would provide additional information of its formation.
XRD analysis was attempted in this work, but the limited size of the BUE hindered this. Theinterference between the BUE and the substrate prevented any useful results.
Better sample preparation of the quick-stop samples would allow more detailed observationof the stagnation zone.

58

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62

Appendix A: Cutting parameters
Cutting parameters for all milling tests.
Vc

fz

Ae Ap Dc

165
165
110
190
150

0,1
0,1
0,1
0,1
0,2 1533
3
3
3

215 0,3 60 3
165 0,1
3
190 0,1
3
150 0,2 15 3
215 0,3 60 3
165
190
150
215

0,1
3
0,1
3
0,2 15 30,3 60 3

165 0,1

3

110
190
150
215

0,1
3
0,1
3
0,2 15 30,3 60 3

165
190
110
150
215

0,1
3
0,1
3
0,1
3
0,2 15 30,3 60 3

165
190
150
215

0,1
3
0,1
3
0,2 15 30,3 60 3

165 0,1
175 0,2110 0,2

3
3
3

Cutting temp SS2343
29401
32 MediumDp1: 3,25 mm cut
32
Dp2: 2 mm cut
32
32
25 Low
Dp1: 8 s
Dp2: 5 s
63 High
Dp1: 1 cut
29475
32 MediumDp1: 3,25 mm cut
32
25 Low
Dp1: 8 s
Dp2: 4 s
63 PD
Dp1: 2 cuts
29477
32 MediumDp1: 3,25 mm cut
32
25 CC
Dp1: 8 s
63 High
Dp1: 1 cut
30324
32 MediumDp1: 1+1 mm cut,
Dp2: 4x2 mm +2x3,25 mm cut
32
32
25 Low
Dp1: 8 s
63 High
Dp1: 1 cut
30320
32 MediumDp1: 2 mm cut
32
32
25 Low
Dp1: 8 s
63 High
Dp1: 1 cut
30321
32 MediumDp1: 2 mm cut
32
25 Low
Dp1: 5 s
63 High
Dp1: 1 cut
29400
32 MediumDp1: 3,25 mm cut
32
Dp2: 3,25 mm cut
32
Dp3: 3,25 mm cut

63

SS2377CORRAX

Dp1: 1,5 mm cut

Dp1: 1,5 mm cut

Dp2: 1,5 mm cut
Dp2: 3 mm cut

Dp1: 1,5 mm cut

Dp1: 1,5 mm cut
Dp2: 3 mm cut

Dp1: 1,5 mm cut

Dp1: 1,5 mm cut
Dp2: 3 mm cut

Dp1: 1,5 mm cut

Dp1: 1,5 mm cut

Dp2: 1,5 mm cut
Dp3: 1,5 mm cut

Dp3: 3 mm cut
Dp2: 3 mm cut

Dp1: 1,5 mm cut
Dp2: 1,5 mm cut

Dp1: 1,5 mm cut
Dp3: 3 mm cut
Dp2: 3 mm cut

Dp1: 1,5 mm cut
Dp2: 1,5 mm cut

Dp1: 1,5 mm cut

Dp1: 1,5 mm cut

Dp1: 3x1,5 mm cut

Dp3: 1,5 mm cut

Dp2: 1,5 mm cut
Dp3: 3 mm cut

190 0,1
3
150 0,2 15 3

32
25 Low

215 0,3 60 3

63 High

Dp2: 1,5 mm cut
Dp1: 8 s
Dp2: 5 s
Dp1: 1 cut
Dp1: 1 cut

64

Dp4: 3 mm cut

Appendix B: Worn edges
The insert edges after low temperature milling in SS2343 are presented in figures below.

29400 Dp1.

29400 Dp2.

29401 Dp1.

29401 Dp2.

29475 Dp1

29475 Dp2

29477 Dp1

30320 Dp1

30321 Dp1

30324 Dp1

The insert edges after medium temperature milling in SS2343 are presented in figures below.

29400 Dp1

29400 Dp2

29400 Dp3

29401 Dp1

29401 Dp2

29475 Dp1
65

29477 Dp1

30320 Dp1

30321 Dp1

30324 Dp1

30324 Dp2
The insert edges after high temperature milling in SS2343 are presented in figures below.

29400 Dp1

29401 Dp1

29401 Dp1

29475 Dp1

29477 Dp1

30320 Dp1

30321 Dp1

30324 Dp1

The insert edges after milling in SS2377 are presented in figures below.

29400 Dp1

29400 Dp2

66

29401 Dp1

29475 Dp1

29477 Dp1

30320 Dp1

30320 Dp2

30321 Dp1

30321 Dp2

30324 Dp1

The insert edges after milling in CORRAX are presented in figures below

29400 Dp1

29400 Dp2

29400 Dp3

29400 Dp4

29401 Dp1

29401 Dp2

29475 Dp1

29475 Dp2

67

29477 Dp1

29477 Dp2

30320 Dp1

30320 Dp2

30320 Dp3

30321 Dp1

30324 Dp1

30324 Dp2

30324 Dp3

68

Appendix C: Cross sections
Cross sections of inserts after low temperature milling are presented in figures below

29400

29401

29475

29477

30321

30324

69

Cross sections of inserts after medium temperature milling are presented in figures below

29401

29475

29477

30320

30321

30324

70

Cross sections of inserts after high temperature milling are presented in figures below.

30320

30320

Cross sections of inserts after milling in SS2377 are presented in figures below.

29400

30321

30320

29475

71

29401
Cross sections of inserts after milling in CORRAX are presented in figures below.

29400

29401

29475

29477

72

3032073

Appendix D: SEM images
Figures 9.80-9.83 show electron images obtained from low temperature milled 30324.

74

Figures 9.84-9.86 show electron images obtained from medium temperature milled 29477.

Figures below show electron images obtained from high temperature milled 29400 (U8968
Dp3).

75

76

Appendix E: Images for EDS analysis
Figures below show the electron images which show where EDS analysis were performed.

Low temp. milled 30321

Figure 9.93. Medium temp. milled 30320

Medium temp. milled 29400 (U9824 Dp1)

Medium temp. milled 29475 (U8932 Dp1)

High temp milled 30320.

High temp milled 30320.

77

Unmachined SS3443.

78

Appendix F: 9.6 Microhardness results
Complete results of microhardness tests.

Average

Average

Average

Average

Average

Series name
SS2343
SS2343
SS2343
SS2343
SS2343
SS2343
SS2343
SS2343
SS2343
SS2343Sample name Hardness
198
202
219
252
190
208
210
201
202
209

Low temp. (INOX U8975)
Low temp. (INOX U8975)
Low temp. (INOX U8975)
Low temp. (INOX U8975)
Low temp. (INOX U8975)
Low temp. (INOX U8975)
Low temp. (INOX U8897)
Low temp. (INOX U8897)
Low temp. (INOX U8897)
Low temp. (INOX U8897)
Low temp. (INOX U8897)
Low temp. (INOX U8897)

1030
1030
1030
1030
1030
1030
29400
29400
29400
29400
29400
29400
Low temp. (INOX U8897) 29400
Medium temp.
30320
Medium temp.
30320
Medium temp.
30320
Medium temp.
30320
Medium temp.
30320
Medium temp.
30320
Medium temp.
30324
Medium temp.
30324
Medium temp.
30324
Medium temp.
30324
Medium temp.
30324
Medium temp.
30324
Medium temp.
30324
Low temp.
30324
Low temp.
30320
79

546
303
426
448
434
436
403
437
403
442
426
318
422.2
0
401
416
339
413
410
399
11182370
336
401
363
274
374.75437
431

Method
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.05
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01

Hardnessincrease (%)

103.8277512
114.354067
107.6555024
108.6124402
92.82296651
109.0909091
92.82296651
111.4832536
103.8277512
102.0095694

HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01

91.86602871
99.0430622
97.6076555
96.1722488
90.90909091
60.76555024
91.86602871
73.68421053
79.3062201
109.0909091
106.2200957

Average

Low temp.
Low temp.
Low temp.
Low temp.
Low temp.
Low temp.
Low temp.
Low temp.
Low temp.
Low temp.

30321
30321
30321
29400
29400
29400
29400
29400
29400
29400

Total average

345
401
403.5
1.1
1484
1521
2018
1905
1.1
884
409

HV 0.01
HV 0.01
HV 0.01
HV 3
HV 3
HV 0.1
HV 0.1
HV 0.01
HV 0.01
HV 0.01

SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
SS2377
Average

29475
29475
29475
29475
29400
29400
29400
29400
29400
29400
29400
29400
29400
29400
30320
30320
30320
30320

462
401
421
454
1.4
1.5
662
161
389
1.5
321
421
478
1.1
490
472
497
484
440.8333

HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01

CORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAX

29401
29401
29401
29401
29401
29401
29401
29475
29475
29475
29475
29475

2.4
403
437
399
418
2.2
423
266
308
380
369
392

HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.0180

65.07177033
91.86602871
93.06220096

95
105.3333333
78.22222222
87.11111111
101.7777778

72.88888889
42.66666667
87.11111111
112.4444444
117.7777778
109.7777778
120.8888889
115.1111111
95.92592593

8.918918919
18.10810811
7.837837838
12.97297297
14.32432432

2.702702703-0.27027027
5.945945946

Average

CORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAXCORRAX

29477
29477
29477
29477
30320
30320
30320
30320
29400
29400
29400
29400
29400

81

367
403
411
418
396
369
429
376
406
408
387
413
416
401

HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01
HV 0.01-0.810810811
8.918918919
11.08108108
12.97297297
7.027027027-0.27027027
15.94594595
1.621621622
9.72972973
10.27027027
4.594594595
11.62162162
12.43243243
8.4

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