bluuebunny/crossref_metadata_2025_split huggingface dataset:
Casting of High Alloy Steels in the Mushy State
Authors: Bramann Horst , Afrath Carsten , Grimmig Tilman , Fehlbier Martin , Bührig‐Polaczek Andreas 
Published: December 2016

In order to broaden the field of application for the innovative thixocasting process, much research is dedicated to the thixocasting of high melting point alloys. The wide property range of modern high alloy steels combined with the productive semi‐solid die casting process opens up new fields of application. The Foundry Institute of the Aachen University has therefore been concentrating on the research of the possibilities and limits of high pressure die casting of high alloy steels in the semi‐solid state. This paper gives an overview of the current work dedicated to thixocasting of steel alloys by a high pressure die casting machine at the Foundry‐Institute of the Aachen University of Technology.In order to understand and describe the material properties in the semi‐solid state, basic test specimens have been investigated. Weak points of tool preheating as well as directional solidification of the produced parts can be controlled by numerical simulation of the temperature distribution inside the dies. In consideration of the outstanding flow properties of semi‐solid steels more complex geometries with accurately defined applications are now being investigated. Extensive metallographical analyses of the pre‐material, the reheated billets and the produced parts have been done to evaluate the viability of the process. The mechanical properties of the specimens outline the outstanding potential of the thixocasting process.
Thixoforging of Steel Using Ceramic Tool Materials
Authors: Behrens Bernd‐Arno , Haller Björn , Fischer Dirk 
Published: December 2016

Today thixoforming processes are mainly established in the production of parts made of aluminium alloys. Compared to high melting alloys the process temperature is low and thus the process is easier to handle. Because of process temperatures up to 1470°C thixoforming of steels demands a sophisticated process control and adapted tool materials. In this field there is still a large need for research. This paper deals with experiences made at the IFUM concerning the thixoforging of steel. The use of ceramic tool materials for thixoforging of steel is presented. For this purpose hybrid dies where a ceramic insert is prestressed with a hot working steel shrink ring as well as different stamp geometries were developed and built up. Different ceramic materials from Si3N4 to ZrSiO4 were tested and evaluated. To prevent an unwanted cooling and oxidation of the slug during its transfer, the transfer is carried out encapsulated in high temperature resistant crucibles that can provide a protective atmosphere. The suitability (e.g. thermo shock resistance) of different materials for the use as transport crucibles was also subject of this research work.The forming experiments were carried out with the institute's hydraulic press. The process logic controller of this press offers the appropriate flexibility and various control modes needed for a sophisticated and reproducible filling of the die. In this way the die filling process of different steels can be tested.
Thixoforging of Steel Alloys ‐ Facility Requirements for Industrial Application
Authors: Siegert Klaus , Messmer Guenther 
Published: December 2016

The article describes some important considerations for an industrial application for the thixoforging of steel alloys. Extensive experience in the forming of aluminium, brass and steel alloys was made with the automated thixoforging unit set‐up at the Institute for Metal Forming Technology. After a brief description of the thixoforging unit, the cycle of automated thixoforging is explained. Beside the demands of reheating in an inert atmosphere, some aspects of process monitoring are described. In relation to this, the installed industrial vision system is presented.The requirements for batch production dies in automated units are focused upon. The results of the experimental forming of steel alloys with two different materials for the thixoforging dies are presented. A comparison of both alloys 1.2714 and CuCrZr is made.
Advanced Processing and Properties of Thixotropic Formed Components Based on Partially Melted Magnesium
Authors: Wagener Wolfram 
Published: December 2016

Contrary to the manufacture of aluminium components in the semi‐solid, thixotropic state the production of magnesium based components by semi‐solid techniques is still uncommon. For this reason, the advantage of this production method is analysed with regard to the commercial magnesium alloy AZ80. The objective of this research is semi‐solid‐casting (SSC) of AZ80 for the production of a light weight component in near‐net‐shape quality and with advanced properties.Using extruded primary feedstock material, the behaviour and the advantages are investigated. Billets with a weight of up to 2 kg are heated up into a semi‐solid state. To avoid any risk of self‐ignition of the material an automatic, temperature controlled induction heating system is used. To achieve an optimum homogeneous grain structure the induction heating power is varied making use of a process control system based on power‐time‐curves. The heated billets are transported in the soft semi‐solid condition from the induction heating system to a die casting machine to produce components with wall thickness’ between 2 and 10 mm. After forming of the components, the influence of heat treatment on the grain structure and especially on the mechanical properties is determined to provide parts with optimised characteristics.To compare the properties of the special globular grain and microstructure, the results of various static and dynamic tests are analysed. It is found that components can be manufactured with a magnesium alloy in a thixotropic state in near‐net‐shape quality, with low porosity and with excellent mechanical properties like elongation of up to 15%.
Structure of Liquid Slags and Ultraviolet/Visible Reflection Spectroscopy of Molten and Glassy Silicates (Fe2O3‐CaO‐SiO2)
Authors: Nowack Norbert , Zebger Ingo , Pfeifer Frank 
Published: December 2016

The first part of this work is a description of the molecular structure of liquid silicates. From the knowledge of the chemical bond, the Men+···O2− bond distance and the Men+/O2− coordination number, the Men+···O2− bond polarity (Me=Ca, Mg, Al, Fe…) of liquid oxide slag systems is derived. There exists a connection between this value and the activity coefficient of an oxide component. We illustrate this connection for important slag systems.The second part of this work deals with the reflectivity of liquid silicates in the ultraviolet and visible spectral range using the reflection angle 0°. For these considerations, we have developed a spectroscopic reflection method (impulse‐flash‐technique). We have investigated the systems CaO‐FeOn‐SiO2 with Fe2O3 ‐contents above 24% (mass percent) and a CaO‐Fe2O3‐flux with an Fe2O3‐content of 60% in the temperature range from 1400 °C to 1500 °C applying an oxygen partial pressure of pO2 = 0.21 bar. The increased reflectivity in the ultraviolet spectral range is based on the very intensive electron transfer (charge transfer bands: CT) from the oxide ion (bound to the respective matrix) to the Men+‐ion (Men+=Fe3+, Mn2+..). The increased reflectivities in the visible spectral range are due to d‐d‐transitions in the Men+‐ion located in Men+‐O2− ‐complexes. This can be proven in the following way. The reflection bands in the visible range are much less pronounced than the CT‐bands in the UV range. In liquid slags complexes with the coordination number 4, Fe3+(O2−)4 were found. In glassy silicates, complexes with the coordination number 6 dominate. The reflection spectra have been analysed quantitatively and related to the molecular structure of the liquid and glassily solidified systems.In the present work, we describe a quantitative correlation between the reflectivity in the UV range and the molar Fe3+‐content. The basic investigations for recording the redox state of liquid silicates during a running metallurgical process are part of this work.
Microstructure and Tensile Properties in Dual Phase and Trip Steels
Authors: Bleck Wolfgang , Papaefthymiou Spyros , Frehn Andreas 
Published: December 2016

Advanced high‐strength steels, like dual phase and TRIP steels, have gained much interest for automotive application. The complex microstructures in dual phase steels, and even more critical, the metastable microstructure in TRIP steels, do not follow the well‐established traditional microstructure‐property relationships for deep drawing steels. The volume fraction of the different phases, the phase distribution, and the stability of metastable phases influence significantly the forming potential.This paper discusses the correlation between different microstructural features and the mechanical properties. The tensile test properties of dual phase steels are governed by the martensite volume fraction, the martensite hardness and to a much smaller extent the martensite island diameter. Both in dual phase and more pronounced in TRIP steels the retained austenite content plays a vital role in determining the formability. The stability of the retained austenite can be described by different methods, it needs to be adjusted according to the forming temperature and the type and amount of strain. In general, multiphase steels require a very strict microstructure control in order to develop predictable forming behaviour.
On the Relationship between Mechanical Properties and Mechanisms of Plastic Deformation in Metastable Austenitic Steels
Authors: Pétein Arnaud , Jacques Pascal J. 
Published: December 2016

The requirements of the automotive industry for materials exhibiting increased structural performances are continuously increasing. These materials must remain ductile during the forming operations while also exhibiting improved strength and energy absorption capacities.New highly alloyed steel grades have been studied for a few years now, due to their exceptional mechanical properties resulting from interactions between dislocation plasticity, transformation plasticity and mechanical twinning.This study deals with the mechanical properties of steel grades presenting high manganese compositions. At room temperature, several phase transformations (γ→α', γ→ɛ and ɛ→α′) were found to occur when the samples are deformed. The effect of different annealing conditions on the mechanical properties and the transformation sequence is analysed. The evolution of the work‐hardening of the samples is interpreted in connection with the kinetics of the phase transformations.
On the Behaviour of Hematite and Graphite Blend during Ball Milling and Heating Up Reduction of Milled Mixture
Authors: Raygan Shahram , Khaki Jalil Vahdati , Aboutalebi Mohamad Reza 
Published: December 2016

The effect of ball milling under argon and air atmospheres on the reaction behaviour of the mixture of sintered hematite and graphite was investigated. Thermo‐gravimetry / differential thermal analysis (TG‐DTA) was adopted to determine the effect of milling time on the reduction process during heating up under Ar atmosphere. The samples were heated at a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained at this temperature for 30 minutes.TGL (thermo‐gravimetry loss) curves showed a decrease of onset temperature of reduction with increase of milling time. XRD patterns of milled samples at room temperature revealed that the peaks of graphite disappeared after 48 hours milling. This represents the transformation of crystalline structure of graphite to the amorphous structure. By increasing the milling time to 72 hours, magnetite peaks appeared in the XRD pattern as a result of reduction of hematite with graphite during milling. However, the amount of magnetite formed during milling process increased as milling proceeded. The powders milled under Ar atmosphere became more active than the powders milled under air and consequently the carbothermic reduction of hematite in powders milled under Ar atmosphere was observed at lower temperatures compared with air‐milled powders. It was observed that the reduction time of hematite in powder mixture was decreased with increase of sintering time of hematite prior to milling.
Oxidation State of Titanium in CaO‐SiO2‐TiOx Slags at 1873K
Authors: Ariyo Chris , Gonzalez Pablo , Holappa Lauri 
Published: December 2016

Oxidation state of titanium was determined in CaO‐SiO2‐TiOx slags in the composition range 25‐53 percent CaO, 27‐46 percent SiO2, 10‐55 percent TiOx at 1873K using gas equilibration method.In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti3+ and Ti4+ contents as well as the activity coefficient ratio of corresponding oxides in the slag.The dependence of the activity coefficient ratio as a function of oxygen partial pressure was determined.
Chromium Oxide Reduction from Slag by Silicon and Magnesium
Authors: Gutiérrez‐Paredes Juliana , Romero‐Serrano Antonio , Plascencia‐Barrera Gabriel , Vargas‐Ramírez Marissa , Zeifert Beatriz , Arredondo‐Torres Víctor 
Published: December 2016

Experimental and theoretical studies were performed in order to estimate the effect of the basicity of the slag as well as the amount of reducing agents on the reduction of chromium oxide from a slag in contact with molten steel at 1600 °C. The aim of this work was to compare the efficiency of magnesium and silicon as reducing agents of Cr2O3. The slag system contained CaO, MgO, SiO2, CaF2 and Cr2O3 together with Fe‐alloys (Fe‐Si or Fe‐Si‐Mg). The maximum Cr yield was about 81% with Fe‐44%Si‐9%Mg and 88% with Fe‐75%Si. That means that the reducing effect of Mg was much better than that of Si. Some experiments were conducted to study the effect of initial Cr in steel on the chromium oxide reduction reaction. Three initial Cr contents were tested (0.15, 2 and 4 mass%). It was found that chrome was partially bound into stable spinel phase MgO·Cr2O3 in the final slag.Thermodynamic estimations were made to determine the effect of process temperature, slag basicity and the amount of reducing agents in the slag on the Cr recovery. The efficiency of Cr reducing agents increased in the order: Si, Al, Ca and Mg. The Cr yield increased with slag basicity and amount of reducing agents.
Twin Roll Casting of Steel Strip ‐ Experiments and Model Considerations on Strip Spottiness
Authors: Büchner Achim R. 
Published: December 2016

Thin strip casting of steel through a twin‐roll caster demands the production of a perfectly homogeneous strip. This requirement is often not fulfilled due to non‐uniform heat contact between the solidifying strip and the rolls in the pool, which leads to temperature inhomogeneities visible at the strip behind the rolls (spottiness). The effect of spottiness is described from experimental observations in terms of contrast between dark and hot spots and of the mean diameter of the hot spots. The contrast is found to depend on roll material, surface roughness and roll velocity. A general dependence on the temperature difference between melt and rolls is observed.Calculations of heat transfer in the liquid and solid pool explain the hot‐dark‐temperature differences. The spottiness visible on the strip after leaving the rolls is initiated in the liquid pool, but it is enlarged by rolling contact differences in the solid pool. A model consideration based on thermally caused bending of the solidified material layers leads to a good coincidence with experimental data of the heat transfer coefficient at hot spots.
An Improved Model for the Longitudinal Peak Strain in the Flange of a Roll Formed U‐Channel developed by FE‐Analyses
Authors: Lindgren Michael 
Published: December 2016

Today one can find cold roll forming (CRF) products in many applications, for example vehicles, furniture and in the building industry. Though CRF is a well known sheet metal process, it is still not entirely understood due to the geometrically complex forming. There are several computer aided engineering (CAE) programs on the market that can assist the tool maker when designing a new CRF machine. However, they are often based on simple formulas when predicting the stress and the strain in the strip.The main objective of this study is to improve formulas for the longitudinal peak membrane strain and the deformation length when a U‐channel is formed. These are important since they can be used to determine the number of forming steps and the distance between them. A two‐level factorial design is done using the finite element analysis to investigate which parameters affect the peak strain and the deformation length. The parameters are then used to build models for the peak strain and the deformation length.
A Constitutive Creep Equation for 9Cr‐1Mo‐0.2V (P91‐type) Steel under Constant Load and Constant Stress
Authors: Nagode A. , Ule B. , Jenko M. , Kosec L. 
Published: December 2016

The creep behaviour of 9Cr‐1Mo‐0.2V (P91‐type) steel was studied at elevated temperatures of 625 to 675 °C. These temperatures considerably exceed the maximum service temperature of this steel, which is approximately 600 °C. Uniaxial creep tests were performed under constant load and constant stress at initial stresses of 120 to 240 MPa. These tests are considered as short‐term tests and they can even be applied for creep lifetime assessment, albeit with certain limitations. However, the main purpose of this work was to find a constitutive creep law that would satisfactorily describe the creep behaviour of P91‐type steel and enable a comparison of the results obtained with both kinds of creep tests, i.e., under constant load and constant stress.It is well known that the minimum creep strain rate of P91‐type steel cannot be satisfactorily described by the simple Arrhenius‐type power‐law constitutive model. Therefore, an improved stress‐dependent energy‐barrier model for the description of the creep behaviour of P91 steel was used. The model showed that there is a small difference in the apparent activation energy between constant‐load and constant‐stress creep tests. The obtained values of the stress‐dependent activation energies are, in both types of test, considerably higher than the activation energy for lattice diffusion. This is in good agreement with the literature data, although the obtained activation energies are not so strongly stress dependent. The Monkman‐Grant relation showed that the minimum creep strain rate is not quite inversely proportional to the time‐to‐rupture for both constant‐load and constant‐stress creep tests.
Evolution of Microstructure and Texture during Hot Torsion of Ferritic Stainless Steels Stabilized by Nb and Ti
Authors: de Oliveira Tarcisio R. , Montheillet Frank 
Published: December 2016

The study was carried out to understand the mechanisms occurring during dynamic recrystallization of hot deformed 11% chromium stabilized ferritic stainless steels and to compare the behaviour induced by various types of stabilization. The experimental temperatures ranged from 800 to 1150°C and strain rates from 10−2 to 15 s−1. The development of the textures and microstructures was analysed using EBSD maps. It was observed that continuous dynamic recrystallization occurs in all materials starting at the onset of straining. Niobium has a more pronounced influence on hardening than titanium during hot deformation. The D2 component was found as the major texture component at the steady state for the torsion tests conducted along the negative shear direction. It was likely to be formed by the combination of straining and growth of the grains exhibiting both low stored energy and low rotation rate of the crystallographic axes. The texture evolution was the main reason for the flow stress behavior during the hot torsion tests.A complementary study was carried out to understand the texture formation occurring during the direct (negative shear direction) and reversed (positive shear direction) hot torsion. After reversion of the shear direction, i.e. during positive shear, the above major texture component is gradually changed into the D1 component. Using the method of Continuum Mechanics of Textured Polycrystals, the stress evolution is explained by the volume fraction changes of each component at various strains, associated with their respective Taylor factors. This simplified approach leads to a good agreement with experimental results.
Increasing Rigidity and Strength using Local Effects of Bead‐on‐Plate Laser Welding Seams
Authors: Schimek Mitja , Meier Oliver , Ostendorf Andreas , Haferkamp Heinz 
Published: December 2016

In order to achieve graded strength properties and to improve the rigidity of metallic materials, side effects of the laser joining process are used. Local physical and geometrical effects which have only been observed as side effects are to be used purposefully. The investigations take place in context of the SFB 675 “high‐strength metallic structures and joints by setting up scaled local material properties”. The energy needed to produce bead‐on‐plate welding seams can be limited to a small area of the workpiece by using a focused laser beam with a diameter of tenths of a millimetre. The heat affected zone of a laser beam is very small. In comparison to other welding procedures, lower heat input is the main reason that basic material characteristics remain unaffected after welding. The progressive development of laser beam sources to higher available laser output power has extended their spectrum of use in the field of joining technologies [1, 2].It should be pointed out that local physical and geometrical effects can be used to achieve specific material characteristics. Bead‐on‐plate laser welding seams were produced to demonstrate that strength and rigidity can be increased in metal sheets. First investigations are carried out on the micro‐alloyed high‐strength steel H340LAD. The sheets were tested using tensile tests and also with 3‐point and 4‐point bending tests. Six different specimens were investigated, one without welding seams and five with different laser based welding seam types. The tensile and bending tests showed that higher forces were needed to rupture or to bend the laser welded specimens. Furthermore, the investigations showed that the strength of the specimens was increased in comparison to the specimens without welding seam.
Turnover of the Soil Organic Matter Amino Acid Fraction Investigated by13C and14C Signatures of Carboxyl Carbon
Authors: Hatté Christine , Noury Claude , Kheirbeik Louay , Balesdent Jérôme 
Published: December 2016

AbstractNitrogenous compounds of soil organic matter constitute a major N reservoir on Earth. Both the world food protein supply produced by agriculture and the global contamination by reactive nitrogen species rely on the dynamics of these compounds. To investigate their dynamics, we used both natural13C labeling and accelerator mass spectrometry (AMS)14C dating of the α-carboxyl amino carbon, which is specific of the amino acid fraction that was extracted from bulk soil organic matter by ninhydrin hydrolysis. We applied this isotopic approach to investigate the age of carboxyl carbon in a maize-cultivated Cambisol chronosequence. Based on a few measurements, we demonstrate the feasibility of this new compound-specific method of investigation of soil carbon dynamics. We show that soil organic matter amino acids can be split into two very distinct dynamic compartments: the majority having a mean age of a few years and a minority having a mean carbon age of several millennia. The latter fraction can be either strongly stabilized in soils, or can arise from microbial utilization of old carbon resources, as predicted by the priming effect theory.