bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Shock Processing as an Advanced Technique for the Surface and Mechanical Resistance Properties Modification of Bioabsorbable Magnesium Alloys
Authors: Ocaña José Luis , González-Carrasco José Luis , Lieblich Marcela , Porro Juan Antonio , Díaz Marcos , Cordovilla Francisco , Angulo Ignacio , Izaguirre Ignacio
Published: December 2018

Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials’ mechanical and surface properties in different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour. On the other hand, Mg and its alloys have gained increasing relevance as natural biomaterials as their mechanical properties are in the same range as those corresponding to natural bone as well as due to their inherent bioabsorbable properties. In the present paper, the application of the LSP technology to biocompatible bioabsorbable Mg alloys suitable for chirurgical implementation is envisaged, the experimental verification of the residual stresses fields induced and the experimental characterization of the surface properties introduced by means of the treatment being specifically considered.
The Effect of Test Temperature on Deformation Microstructure and Fracture Mechanisms in CrMn High-Nitrogen Steels Alloyed (0-3 wt.%) with Vanadium
Authors: Astafurova Elena G. , Moskvina Valentina A. , Maier Galina G. , Melnikov Eugene V. , Galchenko Nina K. , Astafurov Sergey V. , Gordienko Antonina , Burlachenko Alexander , Smirnov Alexandr , Bataev Vladimir
Published: December 2018

A temperature dependence of the tensile mechanical properties, microstructure and fracture mechanism of high-nitrogen Fe-(19-23)Cr-(17-21)Mn-(0-3)V-(0.1-0.3)C-(0.5-0.9)N vanadium-free and vanadium-containing steels was investigated. For all steels, the 0.2% offset yield strength and strain-hardening drastically increase with a decrease in test temperature. This is associated with high interstitial solid solution strengthening of the steels and more pronounced twinning and stacking-fault formation during straining below room temperature. For the vanadium-free steel, a ductile-to-brittle transition was evaluated: at 77K specimens destroy by cleavage mechanism while at room temperature steels show ductile fracture. Vanadium-alloying provides a particle strengthening of the steels and, at the same time, reduce solid-solution strengthening. Increase of vanadium concentration fully or partially suppress brittle fracture of the steels at 77K. Particle strengthening changes interstitial solid-solution effect, dislocation arrangement and slip/twinning relation in vanadium-containing high-nitrogen steels compared to vanadium-free one.
Effect of Al on the Microstructure and Mechanical Properties of Hot-Rolled Medium-Mn Steel
Authors: Han Ding Ting , Xu Yun Bo , Zou Ying , Hu Zhi Ping , Chen Shu Qing , Yu Yong Mei
Published: December 2018

The present investigation was made to study the effect of Al on the microstructure and mechanical properties of hot-rolled medium-Mn TRIP steel (abbreviated as Al-TRIP). As a contrast, a Si-added medium-Mn TRIP steel (abbreviated as Si-TRIP) was also studied. Addition Al in medium-Mn steel can raise Ac3 temperature, which will restrain austenite transformation and expand the two-phase region, promoting Mn and C elements enriched in austenite. In-depth microstructure and mechanical properties analysis were carried out for the hot-rolled Al-TRIP and Si-TRIP steels in this study. The microstructure was characterized by scanning electron microscope (SEM) and electron probe microanalyzer (EPMA). Volume fraction of retained austenite was measured by D/max2400 X-ray diffractometer (XRD). A dual-phase microstructure consisting of ultra-fine grained intercritical ferrite (IF) and lath-like retained austenite (RA) with high mechanical stability was obtained after annealing at 630°C for 2h for Al-TRIP steel. As prolonging the intercritical annealing time, the stability of RA decreased primarily due to the increase of grain size. The tensile test results indicated that the Al-TRIP steel possessed a better combination of tensile strength and elongation compared to Si-TRIP steel. Excellent mechanical properties with yield strength of 790MPa, tensile strength of 1050MPa, total elongation of 35% and UTS×TEL of 39GPa·% was obtained for the Al-TRIP steel.
Characterisation of Precipitation and Coarsening of Carbides during Tempering in a Low Alloyed Quenched and Tempered Steel
Authors: Ju Yu Lin , Goodall Aimee , Davis Claire , Strangwood Martin
Published: December 2018

Low alloy quench and tempered (Q&T) steels plates up to 100mm thick are used in applications such as cranes and earth movers due to their combination of high strength and toughness. In order to ensure that appropriate tempering conditions are used to give optimum properties through thickness in Q&T steels it is desirable to be able to predict the effect of composition and tempering conditions (time and temperatures) on the microstructure and hence the hardness evolution. In this paper, the types and coarsening rates of carbides formed in a low alloyed Q&T steel have been investigated on tempering at 600 °C. It has been found that in the as-quenched condition auto-tempered martensite is present with needle-shaped epsilon and cementite particles, whilst after different tempering times (1 - 16 hours) cementite becomes the stable phase with an elliptical shape, which coarsens with time. Besides, the coarsening of inter-lath cementite with a faster rate is independent from that of intra-lath ones.
The Effect of Heating Rate and Temperature on Microstructure and R-Value of Type 430 Ferritic Stainless Steel
Authors: Jaskari Matias , Järvenpää Antti , Karjalainen Pentti
Published: December 2018

Typical applications of ferritic stainless steels require good formability of a steel that is highly dependent on the processing route. In this study, the effects of heating rate and peak temperature on the texture and formability of a 78% cold-rolled unstabilized 17%Cr (AISI 430) ferritic stainless steel were studied. The cold-rolled sheet pieces were heated in a Gleeble 3800 simulator at the heating rates of 25 °C/s and 500 °C/s up to various peak temperatures below 950 °C for 10 s holding before the final cooling at 35 °C/s to room temperature. Microstructures were characterized and the texture of the annealed samples determined by the electron backscatter diffraction method. The R-value in various directions was determined by tensile straining to 15%. It was established that the high heating rate of 500 °C/s tends to promote the nucleation of grains with the {111} orientations during the early state of the recrystallization. The higher heating rate led to a slightly finer grain size and to a marginal improvement in the intensity of the gamma-fibre texture. A coarser grain size would be beneficial for the formability, but the grain growth was suppressed due to low peak temperatures and a short soaking time. Anyhow, the fast annealing resulted in an enhanced R-value in the transverse to rolling direction. The results indicate that even a short annealing cycle is plausible for producing ferritic stainless steels with the formability properties comparable to those of commercial counterparts.
Challenges of Nb Application in Thermomechanical Processes of Steels for Long Products
Authors: López Beatriz , Pereda Beatriz , Bastos Felipe , Rebellato Marcelo A. , Rodriguez-Ibabe J.M.
Published: December 2018

Nb is a classical microalloying element in the design of thermomechanical treatments in low carbon steels for flat products applications. However, its use in medium-high carbon grades, as occurs in hot rolling of bars, is less common. This is, in part, because of the diversity of characteristics required to those grades of steels and the less knowledge about the function of Nb in these cases. Consequently, less information is reported concerning thermo-mechanical processing of Nb microalloyed steels in long products applications. In this case, it is necessary to consider the singularities related to these processes, such as the short interpass times and the wide range of chemical compositions usually applied on these products. Short interpass times result in high strain rate values that can lead to metallurgical changes on the mechanisms occurring during the hot rolling must be considered. Moreover, the high Carbon contents applied in long products, usually between 0.20–0.40%, can influence the Nb solubility and precipitation in each stage of the process: prior to hot rolling on the reheating furnace, during the process and after hot rolling, depending on the cooling strategy adopted and on the post-rolling heat treatments that can be applied. This paper analyses different singularities associated with the use of Nb microalloying for long products. Several aspects, such as the partial or complete dissolution of the Nb prior to hot rolling, its role in the control of austenite microstructure and its incidence in the final microstructure and mechanical properties, will be considered.
Effect of Ausforming on Creep Strength of G91 Heat-Resistant Steel
Authors: Vivas Javier , Rementeria Rosalia , Serrano Marta , Altstadt Eberhard , San Martín David , Capdevila Carlos
Published: December 2018

The major challenge in a heat-resistant steel is to generate thermally stable microstructures that allow increasing the operating temperature, which will improve the thermal efficiency of the power plant without diminishing strength or time to rupture. The strengthening mechanism in tempered martensitic 9Cr steels comes mainly from the combination of solid solution effect and of precipitation hardening by fine MX carbo-nitrides, which enhance the sub-boundary hardening. This work is focused on the effect of ausforming processing on MX nanoprecipitation, on both their distribution and number density, during the subsequent tempering heat treatment. The creep strength at 700 oC was evaluated by small punch creep tests. The creep results after ausforming were compared to those obtained after conventional heat treatment concluding, in general, that ausforming boosts the creep strength of the steel at 700 oC. Therefore, conventional ausforming thermomechanical treatment is a promising processing route to raise the operating temperature of 9Cr heat-resistant steels.
Environment-Induced Degradation in Maraging Steel Grade 18Ni1700
Authors: Ramkumar K. Devendranath , Gopi G. , Valluri Ravi Prasad , Kumar K. Sampath , Jena Trilochana , Muktinutalapati Nageswara Rao
Published: December 2018

Samples extracted from flow formed tubes made of 18% nickel maraging steel grade C18Ni1750 were subjected to tensile testing at room temperature in laboratory environment at two different strain rates. Testing was carried out in as flow formed as well as flow formed and aged conditions. Aging was carried out adopting four different cycles. Distinct loss of ductility was observed at the lower strain rate in all tested conditions. The embrittlement occurring during low strain rate testing is explained in terms of hydrogen induced damage, hydrogen coming from the moisture in the environment. It is also concluded that the heavy cold work imparted to the material during flow-forming is importantly responsible for the ductility loss observed at low strain rate.
Porosity Developments within 9Cr-1Mo Steel Exposed to CO2
Authors: Coghlan Lawrence , Higginson Rebecca L. , Jepson Mark A.E. , Shin Aya , Pearson Jonathan
Published: December 2018

When 9Cr-1Mo steel is exposed to CO2-rich advance gas-cooled reactor (AGR) gases it forms a duplex oxide which consists of an outer Fe rich layer and an inner Cr rich spinel which provides oxidation resistance allowing the steel to resist the corrosive atmosphere of the plant. The oxide scale develops, growing both into the substrate and outwards from the initial metal/air interface. The spinel develops porosity through the coalescence of Fe vacancies which over time alters the properties of the oxide and potentially allows a transport network to form within the oxide. The porosity of the duplex oxide was measured using scanning electron microscopy of oxides on 9Cr steel samples oxidised in a CO2 atmosphere. Results show that samples which have suffered breakaway oxidation show larger oxide scales with alternating Fe/Cr bands whereas samples which have yet to suffer from breakaway show higher peak porosity values but thinner oxide scales. Furthermore the samples which are currently under protective oxidation show a high max porosity peak in comparison to those which have suffered breakaway.
Middle Shelf During Ductile to Brittle Transition on Ferrite + Pearlite Structure Steel Sheet
Authors: Kawata Hiroyuki , Umezawa Osamu
Published: December 2018

The steels consisting of multi-phase structure show an advantage for their high strength and good formability. The ductile to brittle transition with decreasing temperature has been investigated by Charpy impact test with sub-size specimen for the ferrite + pearlite structure steel sheet. The transition curve of the absorbed energy showed a two-step transition behavior, and the “middle shelf” appeared clearly in the curve. The cleavage-like fracture with few dimples appeared on the fracture surface of the specimens at the middle shelf, and the plastic strain was detected just below the fracture surface. This result suggested that the fracture at the middle shelf propagates with the quasi-cleavage fracture accompanied with plastic deformation. Although the traces of fracture surface corresponded to (001), (011), and (112) bcc-iron planes, the (001) cleavage plane was not dominant for the fracture propagation path at the middle shelf.
Characterization of Hot Deformation Behavior in a 13% Chromium Steel
Authors: Safara Nosar Nima , Sandberg Fredrik , Engberg Göran
Published: December 2018

The behavior of a 13% chromium steel subjected to hot deformation has been studied by performing hot compression tests in the temperature range of 850 to 12000C and at strain rates from 0.01 to 10 s-1. The uniaxial hot compression tests were performed on a Gleeble thermo-mechanical simulator. The best function that fits the peak stress for the material and its relation to the Zener-Hollomon parameter (Z) is derived. The average activation energy of this alloy in the entire test domain was found to be about 557 [kJmol-1] and the dynamic recrystallization (DRX) kinetics was studied to find the fraction DRX during deformation.
Critical Strain for Complete Austenite Recrystallisation during Rough Rolling of C-Mn Steel and Nb-Ti-V Microalloyed Steel
Authors: Maubane Dannis Rorisang Nkarapa , Siyasiya Charles Witness , Banks Kevin Mark , Stumpf Waldo Edmund
Published: December 2018

The influence of roughing strain on the extent of austenite recrystallisation in plain carbon steel and Nb-Ti-V microalloyed steel was investigated. Reheating and roughing simulations were conducted on a deformation dilatometer using industrial heating, soaking times, strain and strain rates. The roughing schedules comprised of varying the pass strain magnitude within a typical roughing temperature range. The double stroke method was used to determine the austenite softening fraction. The austenite grain size, prior to and after rolling, was measured on quenched specimens. Grain refinement was achieved in both steels after all rolling schedules. An applied pass strain of 0.15 was sufficient to completely soften the austenite after the first pass and produced the finest recrystallised grain size. This was attributed to sufficient nucleation sites and driving force for recrystallisation compared to lower strains. Partial recrystallisation occurred after the first pass due to the relatively coarse initial grain size. The steel chemistry played an insignificant role in controlling the recrystallisation kinetics at high roughing temperatures. The through-thickness strain distribution calculated from FEM simulations showed that, for a given applied strain, a similar magnitude of deformation is achieved at the centre of a hot-rolled plate.
Estimation of Impact Toughness Transition Temperatures of As-Quenched Steels
Authors: Pallaspuro Sakari , Kaijalainen Antti , Mehtonen Saara , Kömi Jukka I. , Zhang Zhi Liang , Porter David A.
Published: December 2018

High strength and sufficient toughness are key requirements for modern high-performance structural steels. In an attempt to develop a suitable estimation of impact toughness transition temperatures for as-quenched steels, we investigated the determiners of low-temperature toughness with a group of thermomechanically rolled direct-quenched steels with varying martensite contents. These were produced by altering chemical composition, finish rolling temperature and reduction below the non-recrystallization temperature, i.e. austenite pancaking, and characterised in terms of microstructural constituents, grain size distributions, texture and fractography. Provided the finish rolling temperature is high enough to avoid the formation of granular bainite on subsequent cooling, high levels of austenite pancaking yield the best combinations of low-temperature toughness and strength by effectively refining the size of the coarsest grains and randomizing the texture. While absolutely no direct correlation is found within as-quenched steels between the impact toughness transition temperatures and yield strength alone, T28J and T50 do closely follow a dynamic reference toughness, i.e. the opening stress intensity factor defined by yield strength and the size of the coarsest grains in the effective grain size distribution. This parameter reflects the transition temperatures – the lower the temperature, the lower the reference toughness needed to cause a local brittle fracture. Finally, we show that the impact toughness transition temperatures T28J and T50 of as-quenched steels can be accurately estimated, irrespective of the test specimen orientation, by utilizing just the dynamic reference toughness and the fraction of {100} cleavage planes within ± 15° of the specimen notch plane.
The Study on Welding Technology of 9Ni Steel
Authors: Qu Zhao Xia , Xia Li Qian , Wang Xiao Jie
Published: December 2018

9Ni steel is a low temperature serving ferrite steel, providing high strength and excellent low temperature toughness, which could serve well at-196°C. Therefore 9Ni steel is widely used in storage tanks and transport ships for liquefied natural gas (LNG). Nevertheless there are some challenges in the industrial application, such as hot cracking, cold cracking, magnetic arc blow, etc.. In this paper, the study on the welding technology of 9Ni steel developed by Baosteel is carried out. Firstly the weldability is analyzed through welding thermal simulation using Gleeble 3500 system, Y-groove cracking test, maximum hardness in weld heat-affected zone test. The results prove that 9Ni steel could be welded without preheating. The welding consumables have also significant influence on the performance of the welded joints. In this paper the characteristics of different types of welding consumables, including ferrite base type, austenitic stainless steel type, Ni-base alloy type and Fe-Ni base alloy type are analyzed, then the selecting principle for welding consumables is proposed. Furthermore welding process experiments are undertaken using various welding procedures such as SMAW, GTAW, FCAW and SAW. The results indicate that heat input and interpass temperature should be controlled to ensure a sound weld joint. Finally fracture toughness at-196°C of 9Ni steel and its joint is studied using CTOD test. In conclusion, 9Ni steel developed by Baosteel has good weldability and can meet the requirements of industrial application.
Toward the Development of AHSS for Wear Resistant Applications
Authors: Wolfram Preston , Hensley Christina , Youngblood Ronald , Stewart Rachael , De Moor Emmanuel , Speer John G.
Published: December 2018

Advanced High Strength Steel (AHSS) developments have largely focused on automotive applications using metallurgical approaches to develop retained austenite-containing microstructures in a variety of new steels, using the transformation-induced plasticity (TRIP) effect to achieve better combinations of strength and ductility. These efforts have been extended in recent studies to explore the potential to improve wear resistance, using metastable retained austenite to enhance wear resistance for earth-moving and other applications. This paper provides selected highlights of the authors’ efforts to develop wear resistant steels using AHSS processing approaches. Some attractive product/process development opportunities are identified, and it appears that martensite-austenite microstructures produced using “quenching and partitioning” exhibit increased wear resistance.
Optimization of Pulse-Step Method for Liquid Steel Alloying in One Strand Slab Tundish
Authors: Cwudziński Adam
Published: December 2018

Introduction to the Fe-C-X system: Si, Mn, Al and Nb, Ti, V, B allow the ultimate tensile strength and ductility of steel to be increased at the same time. Therefore, multiphase steels of the TRIP, DP, MART and CP are the steels of the future. The scientific aim of the researches were to obtain new basic information on alloying process of liquid steel in a tundish with the use of the pulse–step method. The facility under investigation was a single outlet tundish being a component of a slab continuous casting machine. Computer simulations of the liquid steel flow and alloy behaviour in turbulent motion conditions were done using the Ansys-Fluent computer program. For generating the computational grids, Gambit program was used. For pulse–step method optimisation two aspects were considered. At first numerical simulations were performed for the selection of the time interval between the pulse feed of the first alloy batch and the continuous feed of subsequent alloy batches in order to maintain the required homogenisation level. Next simulations were done for determination of the mass of the pulse charge that ensures not only the attainment of the 95% homogenisation level, but also the limitation of alloy concentration peaks occurring in the liquid steel and going beyond the 95% homogenisation zone. On the basis of numerical investigations the mixing curves and time mixing for different variants of pulse-step method optimization were obtained.
Characterisation of Long Term Aging in Esshete 1250 Welds
Authors: Stephenson Oscar , Higginson Rebecca L. , Hogg Simon , Knight Jacob , Spindler Sarah
Published: December 2018

In this work, two samples of service grade Esshete 1250 stainless steel, as-received and aged, were characterised to determine the microstructural differences between the parent material and weld in terms of the grain structures and the phases present using XRD, EBSD, SEM and EDS. There was no difference found in the grain structure, but the phases present in the aged weld showed that sigma phase developed during aging.
Properties of Induction Reversion-Refined Microstructures of AISI 301LN under Monotonic, Cyclic and Rolling Deformation
Authors: Järvenpää Antti , Jaskari Matias , Karjalainen Pentti
Published: December 2018

In recent years, the efficient grain size refinement in austenitic stainless steels by the martensitic reversion process and the mechanical properties achieved in a laboratory-scale have been investigated extensively. In order to demonstrate the feasibility of this processing in an industrial-scale, a commercial 18Cr-7Ni-0.15N Type 301LN steel was cold rolled to various relative low thickness reductions (32–56%) to obtain 70–95% deformation induced martensite and subsequently annealed in an industrial-scale pilot induction line at the peak temperatures of 660–820 °C. Some sheets were subsequently cold rolled 10–20% to compare the mechanical properties with those of the commercial strengthened grades. Results showed that the induction annealing at around 700 °C can produce reversed structures with much enhanced tensile and fatigue strengths compared to those of the commercial steel. The stability of the grain-refined austenite is lower than that in the commercial steel, but still cold rolling strengthening remains ineffective.
Austenite Grain Growth Simulation in Welding Heat-Affected Zone
Authors: Fujiyama Naoto , Seki Akira
Published: December 2018

To predict austenite grain growth behavior in the heat-affected zone (HAZ) in low alloy steels, a new calculation model is proposed herein. This model mainly considers the solute-drag effect and pinning effect, which restrain the austenite grain growth. To calculate the solute-drag effect, the grain boundary concentration of each element is obtained by Hillert’s Law. Calculations are performed by simulating the HAZ with a temperature gradient using the phase field method for two dimensions. This calculation demonstrates the possibility of quantitatively predicting the pinning force for welding heat inputs.
3rd Generation AHSS by Thin Slab Technology
Authors: Klinkenberg Christian , Varghese Akhil , Heering Christoph , Lamukhina Olga , Grafe Uwe , Tokmakov Kirill
Published: December 2018

Modern steel making and hot rolling processes like CSP® thin slab technology require precise data on casting and rolling behavior of the produced steel grades. Up today only few data is available for the latest generations of advanced high strength steel (AHSS) grades. AHSS have developed by 3 generations [1, 2]. 1st Generation AHSS as dual phase (DP), complex phase (CP), martensitic (MS) and transformation induced plasticity (TRIP) steel grades are currently applied in automotive industry. 2nd and 3rd Generation AHSS typically have elevated Mn-content as well as Al and Si content. High Mn-content of up to 30% seriously affects casting and forming properties of 2nd Generation AHSS. In particular, the large solidification range of more than 100 K prevents commercial production of these steel grades by continuous casting [3]. 3rd Generation AHSS with reduced Mn-content up to about 12% are currently under development [1-4]. Investigations have been carried out to assess the CSP® thin slab process for the production of such grades. To this purpose solidification and hot forming properties of different alloys having Mn-content up to 10% have been examined by thermodynamic calculations and laboratory testing by hot forming dilatometry. The achieved flow curves match figures achieved on a hot rolling mill.
Effect of the Austenite Interface on Pearlite Transformation Behavior
Authors: Hasegawa Hiroshi , Nakagaito Tatsuya , Funakawa Yoshimasa
Published: December 2018

The effect of the characteristics of austenite interface with ferrite on the pearlite transformation behaviour after intercritical annealing was investigated. Most austenite grains were situated mainly on ferrite grain boundaries and had the Kurdjumv-Sachs (K-S) or near K-S relationship to one of the neighbor ferrite grains before pearlite transformation. The pearlite transformation started mainly from the austenite grain boundary faced to ferrite. The pearlite transformation showed stasis. This indicates that some austenite is stabilized thermally against the pearlite transformation. The fraction of austenite having only the K-S or near K-S interface to neighbor ferrite grains was correspond to the fraction of austenite grains which does not include pearlite. The pearlite transformation was difficult to start from austenite interface having the K-S relationship to ferrite since the interface between austenite grains and ferrite grains was stabilized energetically in the case of their interface having the K-S relationship.
Study on Bainite/Martensite Transformation in Reheated Weld Metals
Authors: Mao Gao Jun , Cayron Cyril , Cao Rui , Logé Roland , Chen Jian Hong
Published: December 2018

A new combination of laser scanning confocal microscope (LSCM) and electron backscattering diffraction (EBSD) with a field-emission scanning electron microscope (SEM) is utilized to study the mechanism of bainite transformation in reheated low carbon bainitic weld metal. The LSCM observations show that laths grow on the surface at various rates, from 30 μm/s to 240 μm/s, which is greatly larger than those referred in literature for bainite. In order to confirm that the laths are bainite and not surface martensite, additional experiments were performed. The crystallographic characteristics of surface bainite were compared with those of bulk bainite obtained during isothermal treatments and those of bulk martensite obtained by water quenching. By means of a dedicated EBSD data-treatment software, orientation relationship, variant selection and packet groups were identified; it was shown that both the surface laths and bulk bainite share the same misorientation, habit plane, and have similar variant distribution. Experiments are running to compare these features with those of bulk martensite. If the distinction between martensite and bainite is successful, the very high growth rates of the surface laths could be used to discuss the displacive/diffusive nature of bainitic transformations.
Numerical Simulation of GMAW Process from the Heat Source to the Weld Pool Formation
Authors: Ogino Yosuke , Asai Satoru , Hirata Yoshinori
Published: December 2018

Gas metal arc welding (GMAW) process is an indispensable technology in various industrial fields. The phenomena during the welding process such as the temperature history of the base metal strongly affect to the properties and performance of the weld joint. It is very important to predict and control the phenomena in the process, however, the phenomena is very complicated and not completely understood. In this study, numerical models of the heat source and the weld pool formation in GMAW process are constructed to visualize the phenomena and predict the welding results of the GMAW process. The heat source model includes the arc plasma and metal transfer phenomena. The temperature, velocity, pressure, and electromagnetic field in the arc plasma and the molten metal are calculated. Influence of the metal vapor from the surface of high-temperature metal is also considered. Input parameters of the heat source model are the welding condition such as the current and the shielding gas used in the experiment. The properties of the heat source such as the heat input distribution, arc pressure distribution and the temperature of the droplet are calculated by the heat source model. These properties are input to the weld pool model. The weld pool model calculates the flow and temperature fields in the weld pool and can predict the penetration shape and the temperature history in the weld joint. These models are applied to pulsed-MAG welding process, the numerical result of the penetration shape shows good agreement with experimental results.
Water Atomized 17-4 PH Stainless Steel Powder as a Cheaper Alternative Powder Feedstock for Selective Laser Melting
Authors: Ghayoor Milad , Badwe Sunil B. , Irrinki Harish , Atre Sundar V. , Pasebani Somayeh
Published: December 2018

Water atomized and gas atomized 17-4 PH stainless steel powder were used as feedstock in selective laser melting process. Gas atomized powder revealed single martensitic phase after printing and heat treatment. As-printed water atomized powder contained dual martensitic and austenitic phase. The H900 heat treatment cycle was not effective in enhancing mechanical properties of the water atomized powder after laser melting. However, after solutionizing at 1315 oC and aging at 482oC fully martensitic structure was observed with yield strength of 1000 MPa and ultimate tensile strength of 1261 MPa which are comparable to those of gas atomized, 1254 MPa and 1300 MPa, respectively. Improved mechanical properties in water atomized powder was found to be related to presence of finer martensite. Our results imply that water atomized powder is a promising cheaper feedstock alternative to gas atomized powder.
Austenitization and Tempering Temperatures Effects on EUROFER 97 Steel
Authors: Testani Claudio , Di Schino Andrea , Alleva Laura , Pilloni Luciano
Published: December 2018

EUROFER 97 is considered as standard steel for the nuclear applications in the case of high radiation density for first wall of a fast breeder reactors. Based on such consideration the microstructural behaviour of EUROFER 97 after thermo-mechanical processing is fundamental, since such materials properties are interesting also for innovative solar plants. In this paper the effect of thermo-mechanical behavior on the mechanical properties of EUROFER 97 has been analyzed by hot rolling followed by heat treatment on laboratory scale.A strong effect of reheating conditions before rolling on the material strength, due to an increase of hardenability following the austenite grain growth is found. A limited effect of the hot reduction and of the following tempering behavior is found in the considered deformation-range investigated. A loss of impact toughness is detected together with the hardness improvement.Mechanical properties are depending on the tempering temperature and an improvement of tensile yield stress (YS) and ultimate stress (UTS) was determined in tensile test carried on at T=550°C and T=650°C, e.g.: YS increase from about 400 MPa for standard EUROFER 97 [1] to about 550 MPa in samples treated by a tempering temperature of 720°C instead of the standard 760°C for EUROFER 97. Same trend has been found for UTS results.
Strengthening of a CoCrFeNiMn-Type High Entropy Alloy by Regular Arrays of Nanoprecipitates
Authors: Stepanov Nikita , Shaysultanov Dmitry , Klimova Margarita , Sanin Vladimir , Zherebtsov Sergey
Published: December 2018

In this paper, we report microstructure and mechanical properties evolution of the CoCrFeNiMn-type high entropy alloy, containing small amounts of Al and C, during cold rolling and subsequent annealing at 700-1100°C. In the initial as-cast condition the alloy has coarse-grained single face-centered cubic (fcc) phase structure. Cold rolling and annealing substantially refine fcc grains; in addition M23C6 type carbides appear. After annealing at relatively low temperatures (≤900°C), these particles are arranged in characteristic arrays aligned with rolling directions. The specific microstructure of the thermomechanically processed alloy is suggested to be the reason of the balanced combination of tensile strength and ductility.
Investigation of Quench Sensitivity in 6xxx Aluminum Alloys
Authors: Lalpoor Mehdi , Vossen Tim , Xhonneux Michael , Schlegel Arne
Published: December 2018

Quench trials were performed on AA6005A and AA6016 alloys to assess the sensitivity of their tensile properties as well as bendability to quench after solution heat treatment. Results indicate that the tensile properties in T4 and in the paint-baked state (2% pre-strain + 185 °C/20 min) are hardly affected by quench rate as long as the exit temperature (Texit) is sufficiently low. The bendability however, appears to be more sensitive to quench rate, and the sensitivity depends on the chemical composition of the alloy. The alloy with a higher excess Si content exhibits higher sensitivity to natural aging which in turn affects the bending and hemming performance of the material. Therefore, it is not only the quench rate which affects the bendability but also the temperature of the material at the end of quench. DSC analysis revealed how cluster formation proceeding the solution heat-treatment (SH) and quench provokes the quench sensitivity.
Microstructure and Texture of Cold Rolled and Recrystallized CrNoNi Medium-Entropy Alloy
Authors: Sathiaraj Gunasekaran Dan , Skrotzki Werner , Immanuel R. Jose , Pukenas Aurimas , Schaarschuch Rolf , Panigrahi Sushanth Kumar , Chelvane J. Arout , Kumar S.S. Satheesh
Published: December 2018

An equiatomic CrCoNi medium-entropy alloy plate was heavily deformed by conventional cold rolling and subsequently annealed at different temperatures. Microstructure and texture evolution of the deformed and annealed sheets were investigated by electron backscatter diffraction and X-ray diffraction. Heavy cold rolling induces an alloy type α-fibre texture with major brass component. This type of texture is indicative of low stacking fault energy of the CrCoNi alloy. Annealing at 700 °C leads to a homogeneously recrystallized microstructure with ultrafine grains of about 800 nm average size. The volume fraction of different texture components is almost similar after annealing at different temperatures. However, the overall texture intensity after annealing is very weak. Finally, in order to understand the microstructure and texture evolution of the CrCoNi alloy, it is critically compared with other low stacking fault energy FCC materials.
Mechanical Behavior of Titanium Alloys under Different Conditions of Loading
Authors: Markovsky Pavlo E.
Published: December 2018

Taking three titanium commercial alloys: commercial purity titanium (c.p.Ti, single-phase α), Ti64 (Ti-6(wt.%)Al-4V, two-phase α+β) and TIMETAL-LCB (Ti-1.5Al-4.5Fe-6.8Mo, both two-phase α+β and single-phase β) as program materials, the influence of phase composition, microstructure and deformation rate (VD, varied from 10-4 to 101 s-1), and deformation mode (compression and 3-point flexure) on the mechanical behavior was studied and compared with data earlier obtained during tensile tests. The size of the matrix phase (alpha- or beta-grains) size and morphology of α+β intragranular mixture were varied using different treatments. Deformation Energy (UD) was used for analysis of the mechanical behavior of the materials tested. It was found that the UD dependencies on deformation rate are different for different methods of loading and are determined by a combination of the phase composition, dispersion, and morphology of the phase constituents. More ductile and less dependent on VD behavior showed c.p.Ti and Ti64 with globular microstructure on all three testing modes, while other materials had some negative features depending on the certain test conditions. Details of mechanical behavior, peculiarities of pores and cracks nucleation causing in final fracture are discussed basing on the results of detailed microstructure study of tested specimens.
Consolidation of Magnesium and Magnesium Alloy Machine Chips Using High-Pressure Torsion
Authors: de Castro Moara M. , Carvalho Amanda Pereira , Pereira Pedro Henrique R. , Isaac Neta Augusta C. , Figueiredo Roberto B. , Langdon Terence G.
Published: December 2018

The high-pressure torsion processing technique was used to consolidate and process magnesium-based chips. Chips were prepared by machining commercially pure magnesium and a magnesium alloy AZ91 separately. Optical microscopy and microhardness measurements showed good consolidation of pure magnesium. The magnesium alloy continued to exhibit the boundaries between the chips even after 5 turns of HPT suggesting poor bonding. The results show that soft chips are easier to consolidate through HPT than harder alloys.
Modification of LPSO Structure in Mg-Ni-Y Alloy with Strontium
Authors: Yang Xiong , Wu Shu Sen , Lü Shu Lin , Hao Liang Yan , Fang Xiao Gang
Published: December 2018

Effects of Sr levels on microstructure of the LPSO structure-containing Mg98.5-xNi0.5Y1.0Srx(x=0, 0.05, 0.10, 0.20 at.%) alloy were studied by SEM/EDS and XRD. Without Sr addition, the Mg98.5Ni0.5Y1.0 alloy consists of α-Mg and LPSO structure and the block LPSO structure is distributed along the grain boundary. After adding 0.05 at.% Sr element into Mg98.5Ni0.5Y1.0 alloy, the amount of dendrites decreased. With the increase of Sr content, the size of α-Mg grains decreases firstly and then increases. Meanwhile, the LPSO structure is refined. The addition of Sr element also results in the obvious increment of the amount of lamellar structure, which stretched from the grain boundary to the matrix. The excessive Sr in high Sr-content alloys participates in the form of Mg-Ni-Y-Sr compound, which is distributed in the vicinity of LPSO structure. In addition, the Sr can also promote the formation of Ni-rich and Y-rich phases.
Investigation of the Effect of Homogenization Practice of 6063 Alloy Billets on Beta to Alpha Transformation and of the Effect of Cooling Rate on Precipitation Kinetics
Authors: Katsivarda Marianna , Vazdirvanidis Athanasios , Pantazopoulos George , Kolioubas Nikos , Papadopoulou Sofia , Rikos Andreas , Spiropoulou Eugenia , Papaefthymiou Spyros
Published: December 2018

A joint research project was accomplished with the aim to determine the effect of homogenization conditions (temperature, time, cooling rate) on the microstructure and hardness of 6063 alloy billets. Homogenization is crucial for the ability to extrude the piece in low cost, but mainly without defects. Thus, it is of importance to determine the most suitable homogenization conditions (temperature, time, cooling rate) and its effect on both microstructure and hardness of 6063 alloy billets. Furthermore, the size and morphology of the AlFeMnSi intermetallic particles (mean diameter, aspect ratio) and the precipitation behavior of Mg2Si constituents are examined in detail via optical (OM) and scanning electron microscopy (SEM). The resulting mean diameter and aspect ratio data generated by such measurements using OM and image analysis of the intermetallics, that are relevant to the extent of beta-to-alpha transformation, are statistically processed with “ANOVA”. Differential Scanning Calorimetry (DSC) tests are used to determine the coherency level of the particles that were precipitated during the different cooling rates and to reveal the potential for resolutioning the precipitates during billet preheating. Samples received from the plant are compared to laboratory samples in order to facilitate the process of optimization the thermal treatment and improve extrudability.
Characterization of Precipitation Evolution in a Zn-Added Al-Mg-Si-Cu Alloy during Artificial Aging at 170 °C
Authors: Zhu Shang , Li Zhi Hui , Yan Li Zhen , Li Xi Wu , Huang Shu Hui , Yan Hong Wei , Zhang Yong An , Xiong Bai Qing
Published: December 2018

A Zn-added Al-Mg-Si-Cu alloy during aging at 170 °C up to 34 h exhibits an interesting age-hardening effect. Small clusters, enriched in Mg and Si, are present in the sample after 0.25 h aging. The β′′ phase is dominant with the peak hardness of 135 HV after aging of 8 h. A decrease in hardness of the alloy occurs with the aging time increasing to 34 h, due to the coarsening of β′′ phase. It is also found that the Cu-containing L phase co-exists with the β′′ phase at this aging condition. The quantitative solute concentrations of the matrix show that the formation of clusters is consistent with the slight lower contents of Mg, Si and Cu compared with the alloy chemical composition, and the present of β′′ and L phase is associated with the further partitioning of Mg, Si and Cu from the Al matrix into the precipitates. No Zn-rich clusters and precipitates are observed and the Zn concentration in matrix has no significant change during aging for up to 34 h. This result means that the major of Zn remains in the matrix as aging continues.
Mechanical and Microstructural Characterization of Powder Medium Entropy Alloy
Authors: Moravcik Igor , Kovacova Zuzana , Kitzmantel Michael , Neubauer Erich , Dlouhy Ivo
Published: December 2018

High and medium entropy alloys are an intriguing new material class, revered for possessing an exceptional combination of primarily mechanical properties. In this scientific contribution, the CoCrNi medium entropy alloy has been produced by a combination of mechanical alloying (MA) and spark plasma sintering (SPS). The properties have been characterized by means of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and tensile testing. The powder after the MA process exhibited nano-grained microstructures with fine chemical homogeneity. After the SPS densification, a full density of the bulk products has been achieved. The microstructure was composed of major FCC phase and minor secondary precipitates. The materials possessed high strength values coupled by reasonable ductility levels, therefore overall satisfactory results.
Creep Features of Ti-600 Alloy at the Temperature of 650°C
Authors: Zeng Li Ying , Zhao Yong Qing , Mao Xiao Nan , Hong Quan , Qi Yun Lian
Published: December 2018

Creep tests were carried out on one kind of near alpha titanium alloy named after Ti-600 alloy at the temperature of 650°C, and with the stresses of 150MPa, 200MPa, 250 MPa, 300 MPa and 350 MPa, respectively. The alloy ingot was conventionally forged and rolled to diameter 18mm bars. The creep samples were cut from the rolling bars and were solutioned at 1020°C for 1 h, air cooling, then aged at 650°C for 8 h, air cooling (STA). Steady state creep rate and the stress exponent n at different stresses were calculated for the alloy. Threshold stress σ0 was introduced to get the true stress exponent p. Creep deformation mechanism was also investigated. The results indicated that the steady state creep rate will increase with the rise of stress, and the creep time will also be shortened at the same time. At 650°C, the threshold stress is 83.8MPa. The value of n and p is 7.7 and 3.3 respectively for the alloy crept at lower stress region (150-200MPa); and which is 2.1 and 4.7 respectively for the alloy crept at relatively higher stress region (200-350MPa). Constitutive equations of steady state creep rate were also established for the alloy crept at 650°C. The creep deformation for the alloy is controlled by dislocation slipping at lower stress region, and which is mainly controlled by dislocation climbing and subordinately controlled by dislocation slipping at higher stress region.
Common Heritable Immunological Variations Revealed in Genetically Diverse Inbred Mouse Strains of the Collaborative Cross
Authors: Collin Roxanne , Balmer Lois , Morahan Grant , Lesage Sylvie
Published: December 2018

Variations in the proportion and number of specific immune cell types among healthy individuals are influenced by both heritable and nonheritable factors. Mouse models, subjected to fewer nonheritable factors than humans, allow the identification of genetic factors that shape the immune system. We characterized immunological trait variability in the Collaborative Cross (CC), a powerful genetic resource of recombinant inbred mouse strains derived from eight diverse founder strains. Of the 18 immunological traits studied in more than 60 CC strains, eight showed genome-wide significant linkage, revealing new genetic loci linked to specific immune traits. We also found that these traits were highly subject to heritable influences. As for humans, mouse immunological traits varied as a continuum rather than as discrete immunophenotypes. The CC thus represents a useful resource to identify factors that determine immunological variations, as well as defining other immune traits likely to be heritable in humans.