Advanced High-Strength Steels: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Tilmann Hickel, Max-Planck-Institut fuer Eisenforschung GmbH; Wolfgang Bleck, RWTH Aachen; Amy Clarke, Colorado School of Mines ; Young-Kook Lee, Yonsei University; Matthias Militzer, The University of British Columbia

Monday 6:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr

F-1: 3D Micromechanical Modeling of Dual Phase Steels Using the Representative Volume Element Method and Response Surface Methodology: Parametric Study: Tarek Belgasam1; Hussein Zbib1; 1Washington State University
    Dual Phase (DP) Steels have been receiving worldwide attention as playing an important role in automotive industries due to their light density for weight saving and also for fuel saving and decreasing emissions. Recently, studies on developing DP steels showed that the combination of strength/ductility could be significantly improved after changing the volume fraction and grain size of phases in the microstructure depending on microstructure properties. Consequently, steel manufacturers who develop DP steels are interested in predicting the microstructure properties relationship for optimization of microstructural design. In this work, a microstructure-based approach by means of representative volume elements (RVEs) is built to study the flow behaviour of DP steels using virtual tension tests of RVE to achieve the desired mechanical properties. Microstructures with different martensite and ferrite grain size, martensite fractions, Carbon content in DP, and morphologies are studied in 3D RVE approaches as microstructure parameters. The effect of these microstructure parameters on the combination of strength/ductility of DP steels has been investigated by using Response Surface Methodology (RSM). Response surface contours were constructed for determining the optimum conditions for a required combination of strength/ductility. The verification experiment is carried out to check the validity of the developed model that predicted combination of strength/ductility.

F-2: Atom Probe Tomography Studies of Complex Oxide Formations in Oxide Dispersion Strengthened Steels: Dallin Barton1; Monica Kapoor2; Florian Vogel1; B. Chad Hornbuckle3; Kris Darling4; Gregory Thompson1; 1University of Alabama; 2National Energy Technology Laboratory; 3Army Research Laboratory ; 4Army Research Laboratory
    A series of bulk nanostructured Fe-Ni-Zr and Fe-Ni-Y oxide dispersion strengthened (ODS) alloys were synthesized using high energy mechanical alloying and consolidated using high temperature equal channel angular extrusion. After which the alloys were subjected to heat treatments up to 1000 deg. C. The resultant microstructures were found to be composed of nano/ultrafine or micrometer-sized grains with larger intermetallic precipitates and small Zr or Y oxide clusters. Atom probe tomography revealed the oxide clusters to consist of a complex chemistry with a radially dependent concentration of the different metallic oxide species. As one moved within the oxide precipitate, the oxide continually enriched with ZrO or YO dependent on the material type. The formation of the oxide with the different metallic species is discussed in terms of the thermodynamic energies of formations.

F-3: Carbide Banding Formation and Prevention in 52100 Bearing Steels: Ersoy Erişir1; Oğuz Bilir1; Ahmet Gezmişoğlu1; 1Kocaeli University
    Influence of heat treatment process on microstructure of a AISI E52100 steels was investigated. In practice, carbide banding, carbide segregations and carbide network remain after partial austenization of bearing steels in intercritical region. Inhomogeneous distribution of coarse carbides with inclusions shortens lifetime of bearings due to lowering wear resistance. This study proposes a new heat treatment cycle that aims to achieve higher wear resistance via better dispersion of fine carbides. The new heat treatment step after cold deformation resulted in better carbide dissolution during austenization. Increasing the austenitizing temperature and reprecipitation of carbides in after partial austenization reduced the degree of banding. This new step involves quenching after austenitizing and presents initial martensitic structure before partial austenization. The microstructural characterization was performed using light microscope, scanning electron microscope and XRD. Thermodynamic and kinetic calculations were performed to predict the carbide dissolution during the heat treatment process.

F-4: Cold Deformation Behaviour of Ultrafine-grained Dual Phase Steel Manufactured with Use of a Dynamic Austenite-ferrite Transformation: Dominik Dziedzic1; Krzysztof Muszka2; Janusz Majta2; Peter Hodgson3; 1University of Cambridge; AGH University of Science and Technology ; 2AGH University of Science and Technology; 3Deakin University
    Application of the dynamic austenite to ferrite transformation is a promising way to produce high strength steels via ferrite grain refinement. Dual phase steel sheets were produced with the application of this transformation. Different zones were identified within the cross section of the rolled band: an intercritical deformation zone, and zones of the dynamic austenite to ferrite transformation with high, intermediate and low nucleation density. Correlations between the proportion of these zones and processing parameters were described. Such material was subjected to cold rolling. Deformation inhomogeneity was observed with the use of digital image correlation. The contribution to ductility of each microstructural layer was assessed.

F-5: Controlling Springback in Dual-Phase Steels: Milan Agnani1; Peter van Liempt2; Jilt Sietsma1; Zaloa Arechabaleta1; 1Delft University of Technology; 2Tata Steel Research, Development and Technology
    Advanced High Strength Steels (AHSS) are extremely suitable for lightweight automotive applications. AHSS forming is, however, a challenge for the car companies, which cannot predict springback –strain relaxation after release of the forming stresses- accurately. Besides the elastic part, there is an additional component of the total relaxed strain, which significantly contributes to the springback magnitude. This additional strain component is the so-called anelastic strain and is caused by limited reverse glide of dislocations during load removal. The higher the dislocation density, the larger the anelastic contribution, but adequate quantitative prediction is at the moment not feasible. Moreover, multiphase AHSS will show specific anelastic dislocation behaviour in each constituent. The present work aims to understand the dislocation behaviour in ferrite and martensite when both phases are present in different volume fractions. A physically-based model is coupled with mechanical and nano-indentation experiments to describe the dislocation behaviour, both qualitatively and quantitatively.

F-6: Design of Ultra-high-strength Fe-Cr-Mn-Ni-N-C Stainless Steels with Enhanced Ductilities: Marco Wendler1; Michael Hauser1; Olena Volkova1; Javad Mola1; 1TU Freiberg
    High-interstitial austenitic stainless steels with insufficient mechanical stabilities and poor tensile properties at room temperature were made ultra-high-strength by thermal or thermo-mechanical treatments. The thermal treatment was similar to Quenching and Partitioning (Q&P) processing but involved subzero treatment in the quenching step to obtain a partially martensitic microstructure. For steels with very low martensite start temperatures in which the required fraction of martensite could not be obtained by a subzero treatment, plastic deformation at -40 °C was used to induce martensite. Martensitic-austenitic steels obtained by the preceding methods were subsequently heat treated at 450 °C to temper the existing martensite and allow for the partial diffusion of carbon and nitrogen to the co-existing austenite. For the Q&P-treated variant, the yield strength, tensile strength, and total elongation at room temperature were 1050 MPa, 1550 MPa, and 22%, respectively. The enhanced ductility was due to the raised stability of the remaining austenite.

F-7: Effect of Austenite Grain Size on Deformed Microstructures and Tensile Properties of Austenitic Fe-24.5Mn-4Cr-0.45C Alloy: Sang-In Lee1; Hyeon-Seok Lim1; Byoungchul Hwang1; 1Seoul National University of Science and Technology / Department of Materials Science and Engineering
    In recent years, austenitic high-Mn steels for cryogenic applications have been increasingly used because they have excellent cryogenic-temperature mechanical properties which are comparable to expensive alloys such as austenitic stainless steels, 9% Ni alloys, and Ni-based Invar alloys. However the yield strength of high-Mn steels is not as high as those of other advanced high strength steels. During the deformation of austenitic high-Mn steels, various deformation behaviors such as mechanical twinning, ε-martensite transformation and dislocation gliding occur in accordance with the stacking fault energy (SFE). Since the austenite stability of high-Mn steel is strongly affected by alloying elements and grain size, however, the deformation behavior appears differently according to the alloy systems investigated by researchers. In the present study, Fe-Mn-Cr-C based austenitic high-Mn steels with different grain size were fabricated by varying annealing temperature, and then the effects of grain size on deformation behaviors and tensile properties were systematically investigated.

F-8: Effect of Initial Microstructure on the Grain Size of “Warm Deformed” 4140 Steel: Sammy Tin1; 1Illinois Institute of Technology
    Steels possessing ultra-fine or sub-micron grain sizes have been shown to possess enhanced mechanical properties, but are difficult to process into physically large parts. In an effort to develop a robust thermo-mechanical processing route for producing steels with sub-micron grain sizes, the effect of “warm” deformation on ferritic, bainitic and martensitic starting microstructures of 4140 steel were investigated. The grain refinement characteristics and microstructural changes were quantified in these structures as a function of effective strain and temperature. Due to the homogeneous distribution of fine carbides, the billet material with the bainitic and martensitic microstructures were more amenable to the formation of sub-micron grain structures following recrystallization when compared to the ferritic samples. Experimental results will be presented and mechanisms responsible for the different grain refinement behavior of 4140 steel will be discussed.

F-9: Effect of Plastic Deformation at Elevated Temperatures on the Hardenebility of Boron Steels: Mehmet Özyiğit1; 1Eregli Iron & Steel Works, Co
    Boron alloyed steels mostly used in hot stamping process because of their better hardenability properties. While performing press hardening process high temperature plastic deformation and quenching step occurs together, deformation quantity and deformation temperature range gain importance. Because these parameters directly affect cooling rate to obtain proper final microstructure and mechanical properties. In this work; hot stamping process was simulated by GLEEBLE 3500 materials simulator with different plastic deformations at constant temperature range. Thermo-mechanically treated samples were characterized by using light optical microscope (LOM) and scanning electron microscope (SEM/EBSD). Tensile strength and hardness values were obtained. The experimental data showed that deformation percent and deformation at elevated temperature are very important parameters to obtain proper final microstructure and mechanical properties. Test results show that, increased deformation ratio hardens the transformation tendency. So hot stamping process modifications and developments gain importance day by day by improvement on materials sicence.

F-10: Effects of Deformation on Hydrogen Solubility and Diffusion in Al-alloyed Fe-Mn Alloys: Claas Hüter1; Siaufung Dang1; Xie Zhang2; Albert Glensk2; Robert Spatschek1; 1Forschungszentrum Jülich; 2MPIE
    We discuss hydrogen solubility and diffusion in aluminum alloyed Fe-Mn alloys. The systems of interest are deformed tetragonally and isotropically. From ab initio modelling, we obtain solution energies, then apply Oriani’s theory which reflects the influence of Al alloying as trap site diffusion. This approach is complemented by qualitative considerations based on the minimum energy paths and energy barriers for hydrogen diffusion. Both for diffusivity and solubility of hydrogen, we find that the influence of the substitutional Al atom has local chemical and volumetric and also nonlocal volumetric contributions.

F-11: Effects of Microstructure on the Strain Rate Sensitivity of Advanced Steels: Rakan Alturk1; Steven Mates2; Fadi Abu-Farha1; Zeren Xu1; 1Clemson University; 2National Institute of Standards and Technology
    Computer aided engineering (CAE) analyses of vehicle body structure performance are critically dependent upon the accuracy of material data acquired over strains rates that span from quasi-static to intermediate to high (0.001/s - 1000/s). In this work, the effects of the phases in the microstructure on the flow behavior of steels when loaded at high strain rates were investigated. The investigated steels were particularly selected to cover a wide array of microstructures (phases): ferrite-only, austenite-only, ferrite + austenite, ferrite + martensite, ferrite + martensite + austenite. The materials were deformed at two selected rates: quasi-static and high rate using the Kolsky Bar. With the aid of digital image correlation (DIC), the effect of strain rate on the different mechanical properties and the strain evolution was studied. Differences in rate-dependence among the investigated steels, and the relationships to the phases present in their microstructures, are discussed in detail.

F-12: Excellent Mechanical Properties Balance of Fine 0.1C-2Si-5Mn Fresh Martensite and Ferrite+Austenite Steels: Shiro Torizuka1; 1University of Hyogo
    It is very difficult to emerge a steel which has an excellent total balance of high strength, high ductility with both uniform elongation and local elongation, and high toughness (Charpy impact energy). That is because these properties are in the trade-off relation. Figure 1 shows the Banana curve representing the relationship between tensile strength and total elongation. Tensile strength (TS) increases, total elongation (TE) decreases. Therefore, TSxTE =20000MPa% is said to be limit of the balance. Development of the steel with TSxTE>30000MPa% is a common target for researchers in the world5). 0.1%C-2%Si-5% Mn steels have a high tensile strength of more than 1400MPa and a high total elongation of 17% and are considered to be very attractive in industrial application. However, the mechanism of the excellent tensile strength and ductility balance is not clarified. To investigate the mechanism, transformation behavior and work hardening behavior were examined.

F-13: In-situ Synchrotron X-ray Diffraction Study on the Micromechanical Behavior of Medium Manganese Transformation-induced Plasticity Steel at Low Temperature: Minghe Zhang1; Yandong Wang1; Longfei Li1; Qingbao Wu1; Fangmin Guo2; Yang Ren2; 1University of Science and Technology Beijing; 2Argonne National Laboratory
    A 0.1C-10Mn transformation-induced plasticity steel with fine-grained duplex ferrite-austenite microstructure was obtained annealing at 600 ℃ for 1 h. In situ synchrotron high-energy X-ray diffraction technique was used to investigate the micromechanical behavior of experimental steel at low temperature (-50℃) via measurement of phase fractions and phase lattice strains during deformation. Lüders band-promoted martensitic transformation was observed. After the Lüders band propagated, the volume fraction of austenite decreased gradually until the specimen failed. The {211} lattice strains along the LD of the constituent phases (ferrite and martensite) with similar crystal structures were determined by separating their overlapped diffraction peaks. The load partitioning was established based on the lattice strain of {211}α , {211}αʹ and {311}γ planes. The effective load partitioning among the constituent phases promotes sample ductility at low temperature.

F-14: Influence of Asymmetrical Cold Rolling on Crystallographic Texture of σ-TRIP Steels: Ramón Botelho1; Eustáquio Baêta1; Leonardo Araujo2; Luiz Paulo Brandao1; 1IME; 2Coppe, UFRJ
    The σ-ferrita phase could be obtained in TRIP steels due to the substitution of aluminum to silicon, resulting on a high strength steel with 1 GPa and an elongation of 23%. Furthermore, simulations on ThermoCalc® shown that the niobium is capable of reduce the free carbon and optimize the formation of σ-ferrite in these materials. TRIP alloys containing 5.6% Al and 0.6% Nb were casted to study the influence of thermomechanical processing on microstructure and crystallographic texture (XRD), by symmetrical hot rolling and symmetrical and asymmetrical cold rolling. The conclusion is that the niobium increased the presence of delta-ferrite and symmetrical rolling led to an optimum crystallographic orientation, reaching good mechanical forming and high strength, as previewed.

F-15: Investigating Deformation Mechanisms in TWIP by Marciniak Multiaxial Testing: Brian Lin1; Adam Creuziger1; Timothy Foecke1; 1National Institute of Standards and Technology
    Manufacturers are often provided with only the uniaxial properties of a sheet metal from suppliers. However sheet metal forming processes are complex and the uniaxial data does not account for these complicated strain paths. For the automobile industry interested in utilizing advanced high strength steels, this often involves a number of costly die try-outs. The multiaxial stress-strain response of TWIP980 sheet metal of 1 mm thickness was investigated in balanced biaxial using a modified Marciniak punch. The local strain behavior during testing was captured with digital image correlation and the local stress was measured by x-ray diffraction. The local strain-hardening behaviors are compared,where the transverse direction was observed to be slightly harder than the rolling direction. The observed anisotropy in hardening produced a consistent failure during balanced biaxial loading and electron backscatter diffraction microscopy was used to compare the microstructure and active deformation mechanisms between the two directions.

F-16: Mechanical Evaluation of Hypo and Hypereutectic Chromium Carbide Hard Facing Steel: Yasser Fouad1; Bakr Rabeeh2; Hamad Alharbi1; 1King Saud University; 2German University in Cairo
    The abrasion resistance and mechanical performance of three selected hard-facing alloy grades reinforced with primary chromium carbides, complex carbides and tungsten carbides were studied. Microstructure characterization and surface analysis were made using optical and scanning electron microscopy. The results showed that the wear resistance is determined by the size, shape, distribution and chemical composition of the carbides, as well as by the matrix microstructure, highest wear resistance was obtained from tungsten carbides chromium tungsten carbides presence in a fishbone shape type of M₆C and presence of excessive stress cracks which causes law bending ability while for chromium carbides and Chromium Molybdenum carbide the presence of primary carbides M₇C₃ and formation of complex carbides Mo₂C in an austenite eutectic matrix offered accepted bending strength and wear resistance approximately 14 times more than for carbon steel and 7 times more than for alloyed quenched and tempered steel.

F-17: Microstructure-based Modeling of Tensile Properties in High-strength Pipeline Steels: Byoungchul Hwang1; Sang-In Lee1; Seung-Yong Lee1; Hwan Gyo Jung2; 1Seoul National University of Science and Technology; 2POSCO
    High-strength pipeline steels recently developed for severe regions are required to have high deformability as well as excellent low-temperature toughness and weldability to improve the fracture resistance to sudden deformation and fractures caused by heavy storms, earthquakes, and seismic sea waves. Since new design methodology so-called strain-based design was introduced in pipeline steels, therefore, many studies were are currently underway. In order to install pipeline at the severe region, the use of the pipeline steels with high deformability is perhaps most important. Because the high-strength pipeline steels contain complex microstructures dependent on the chemical composition and processing conditions, however, it is very difficult to characterize the microstructure classified according to the morphological features and to predict tensile properties associated with deformability. Accordingly, the present study aims to predict the tensile properties based on microstructural factors in various high-strength pipeline steels.

F-18: Microstructure and Mechanical Properties of GMAW Welds in TWIP Steels: Alexander Zaddach1; Yen-Chih Liao1; Zhaoqian Liu1; Carlos Cardenas2; Diego Lozano2; 1Lincoln Electric; 2Metalsa
    Twinning-induced plasticity (TWIP) steels are being considered for a range of applications due to their high strength, ductility, and energy absorption abilities. However, their high alloy content relative to conventional steel alloys presents unique challenges for welding processes utilizing filler metals, which have only begun to be explored. In this work, gas metal arc welding with low alloy, austenitic stainless, and duplex stainless steel filler metals was used to join TWIP steel sheet. The resulting weld metal microstructures and the mechanical properties of the weld metal and heat-affected zone will be discussed.

F-19: Modeling the Interplay between Transformation and Plasticity in Low-carbon Steels. A Micro-level Constitutive Model / RVE Approach: Manuel Petersmann1; Georges Cailletaud2; Thomas Antretter1; 1Montanuniversitaet Leoben; 2Mines ParisTech
    To predict the macroscopic behavior of advanced high strength steels, their highly heterogeneous microstructural features must be taken into account. The challenge in writing a constitutive model is to depict microstructural interactions without spatial resolution. We propose a constitutive model on the microscale based on the hierarchical microstructural pattern of low-carbon steels (see e.g. Morito et al. 2006), taking into account all crystallographic variants and their interactions. Phase stresses are separately regarded by using the beta-rule (Cailletaud and Pivlin). The model is applied to a polycrystal RVE with random orientations and periodic boundary conditions in order to get the effect of mutual interaction between grains. Tension compression asymmetry and the transformation related backflow, observed in experiments (Nagayama 2003) are investigated.

F-20: Modelling of Hot Deformation Behavior during Ingot Breakdown Process of Medium Carbon Low Alloy Steel Using Hansel-Spittel Approach: Kanwal Chadha1; Davood Shariari1; Mohammad Jahazi1; 1ETS
    In the present work, modeling of hot deformation behavior was carried out in medium carbon low alloy steels having dendritic microstructure as starting material. Uniaxial hot compression tests were performed on Gleeble-3800 thermomechanical simulator over a wide range of temperatures (1200C to 1050C) and strain rates of (0.2s-1 to 2s-1). The deformation behavior and strain rates were selected on the basis of actual ingot break down process during forging. The results from compression tests were taken as the basis for determination of the analytic function of flow stress for deriving Hensel-Spittel equations. Analysis of the effect of strain rate and temperature on material flow behavior compared Hansel- Spittel and experimental data. The modeling equations were developed in order to find the dynamic recrystallization volume fraction. The comparative study of both these models is presently been analyzed in the framework of classical nucleation theory.

F-21: Multi-stage Martensitic Phase Transformation in Steel/Copper Nanolaminates: An In Situ X-ray Study: Kaiyuan Yu1; Yadong Ru1; Yang Ren2; Lishan Cui1; 1China University of Petroleum-Beijing; 2APS, Argonne National Laboratory
    Nanolamellar high-carbon-steel/Cu composites are fabricated by hot pressing, rolling and wire drawing. Cu layers (100 nm) suppress the growth of the steel layers (100 nm) above austenization temperature, and the subsequent quenching and partitioning processes introduce a large amount of nanosized retained austenite in steel. Stress- and strain- induced martensitic transformation of the retained austenite is characterized by in situ tensile tests under synchrotron X-ray at different temperatures. The transformation rate of retained austenite is drastically higher during the stress-induced regime than the strain-induced regime. Unusual multi-stage yielding is observed, which is attributed to stress-induced transformation that occurs in a manner of Luders band. A deformation mechanism map of the composites is proposed.

F-22: Orientation Dependence of Microstructure and Texture Evolution during Tensile Testing of a TWIP Stainless Steel: Reza Rahimi1; Olena Volkova1; Horst Biermann2; Javad Mola1; 1Technical University of Freiberg-Institute of Iron and Steel Technology; 2Technical University of Freiberg-Institute of Materials Engineering
    Surface contamination and loss of surface smoothness are common issues encountered during in-situ tensile tests in scanning electron microscope (SEM). To overcome these limitations, microstructure and texture evolution by tensile deformation of an austenitic stainless steel was studied by sequential tensile deformation in a tensile testing machine and SEM examinations. After each tensile deformation step, the contamination due to the preceding SEM examination and the roughness caused by the deformation were removed by a light polish. SEM examinations consisted of electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) of grains with different crystal directions parallel to the tensile direction. EBSD results allowed to represent the evolution of the crystal axis parallel to the tensile direction by arrows on an inverse pole figure. Furthermore, the tendency of grains with different orientations to exhibit wavy or planar glide features, in particular deformation twinning, was evaluated by EBSD and ECCI examinations.

F-23: Review of Bake Hardening Mechanisms of Ultra Fine Grained and Coarse Grained Low Carbon Steel Sheets: Uma Gupta1; Vishnu Sharma1; Malay Banerjee1; 1MNIT Jaipur
    Safety regulations and light weight design demands has resulted in increasing application of high strength steels in structural components of an automotive. Ultrafine grained (UFG) steels are expected to be used in the future as structural materials in automotive industry due to unique combination of high strength and toughness, which results in an increase in strength to weight ratio. A number of factors contribute to increase in yield strength during bake hardening which depend on carbon content, alloying elements and manufacturing procedure, hot rolling and cooling parameters, heat treatment parameters, prestrain, aging temperature and time etc. It has been reported in literature recently that bake hardenability is more pronounced in case of ultra fine grain than coarse grain (CG) steel due to lower grain size. In this review, we will discuss various bake hardening mechanisms prevailing in UFG and CG steels.

F-24: Role of Initial Microstructure in Micro Constituents of Dual Phase Steels: Ersoy Erişir1; Oğuz Bilir1; 1Kocaeli University
    In recent years, there have been intense study for dual phase steels since their multiphase character can help to achieve good strength-ductility properties along with low cost. In this study, effect of initial microstructure before annealing and quenching from a temperature between A1 and A3 is studied for medium carbon low alloyed steel. Kinetics calculations using the DICTRA software were performed to obtain the partitioning of alloying elements during intercritical annealing experiments. Ferrite+pearlite and martensite initial microstructures intercritically annealed at several temperature and duration and quenched. Effect of both intercritical annealing temperature, duration and initial microstructure were studied. Microhardness of martensite and ferrite in final microstructure is investigated. Lower hardness difference between martensite and ferrite may be a potential to enhance fracture toughness of dual phase steel.

F-26: Tension-compression Asymmetry and Relationships to the Microstructure in Advanced High Strength Steels: Jun Hu1; Fadi Abu-Farha1; 1Clemson University
    In modeling sheet metal forming and springback, the inputs for calibration, such as stress-strain curves and Young’s/unloading modulus, are typically based on the uniaxial tension case; in other words, material behavior is assumed to be “symmetric” under both tension and compression loading conditions. In this work, we shed some light on this assumption via a comprehensive experimental investigation on the tension–compression asymmetry in several grades of dual phase steels, including DP590, DP780, DP980, and DP1180. The differences in the macro behavior of these grades are correlated to the different ferrite-to-Martensite phase fractions. A ferritic mild steel and a martensitic steel were also considered as references for the comparison. The microstructures of the target steel grades were examined and compared with each other to demonstrate that the tension–compression asymmetry arise not only from crystallographic texture but also from the directional substructure induced by the severe pre-straining.

F-27: Nano-sized Intermetallic Kappa Phase Strengthening in Al-alloyed Steels for Automotive Applications: Wenwen Song1; Wolfgang Bleck1; 1RWTH Aachen University
    In the present work, we report the first-time direct observation of the early-stage kappa phase precipitation from austenitic matrix in steels. The L’12 type kappa phase formation was investigated by a combined approach of in situ high energy synchrotron x-ray diffraction and small angle neutron scattering. Both the synchrotron x-ray diffraction and small angle neutron scattering results show the ordering effect at the early stage of kappa phase formation during annealing at 600 °C in Fe-30Mn-8Al-1.2C steel. The neutron scattering further shows that the early-state ordering of the kappa phase is only 9 Å in radius in the 1 min aged sample. The coherent nano-sized kappa phase precipitated from the austenite matrix contributes to attractive mechanical properties in Fe-Mn-Al-C austenitic steels for automotive applications. By an effective microstructure control, an improved combination of strength and ductility can be achieved, compared with conventional HSLA, DP, TRIP and the micro-alloyed steels.