Advanced High-Strength Steels: Processing of Advanced Steels
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
Thursday 8:30 AM
March 2, 2017
Location: San Diego Convention Ctr
Session Chair: Dirk Ponge, Max-Planck-Institut für Eisenforschung; Mingxin Huang, The University of Hong Kong
Properties and Applications of Industrially Processed Hot Rolled High-manganese TWIP Steels: Thorsten Roesler1; Maximilian Nagel1; Johan Driessen1; Andreas Tomitz1; Jens Overrath1; Harald Hofmann2; Helmut Richter2; Hans Ferkel2; 1Thyssenkrupp Hohenlimburg; 2Thyssenkrupp Steel Europe
Austenitic high-manganese TWIP steels have been produced on an industrial scale in the recent years. Thus a substantial know-how for the technical challenges in continuous slab casting, slab adjustment, hot-rolling and pickling was accumulated within the ThyssenKrupp Steel Europe AG and its subsidiary Hoesch Hohenlimburg GmbH. These steels expose a remarkable light-weight design potential compared to conventional ferritic and multiphase high strength steels and a cost saving potential compared to forged aluminum components. Yet this new class of steels didn’t establish itself sustainably within the automotive industry. In this article frequently arose questions in part layout, computer aided design, forming and welding of parts and assemblies made of high manganese twip steels is illuminated and solution paths are shown.
Hot Stamping Process for Steel Parts with Higher Ductility: Ersoy Erişir1; Oğuz Bilir1; 1Kocaeli University
Hot stamping has recently attracted the attention of the automotive industry, because it possesses good strength and ductility for safety parts in thinner sections. However, hot stamping process requires full austenization before the stamping step. Since any temperature higher than 780°C is not suitable for Zn galvanized steels, Al based coated steels are preferred. In this study, hot stamping is carried out via partial austenization heat treatment at temperatures between A1 and A3 for 22MnB5 and 26MnB5 steels. The microstructural studies were made using light microscope, SEM and X-ray diffraction. Optimal martensite volume fraction and ductility/strength relation was tried to be find. It was seen that highest ultimate tensile strength times total elongation (MPa*%) may be achieved with dual phase hot stamped steels compare to conventional cold formed steels. Thus, dual phase microstructure has a potential to be used for manufacturing of control arm part with thinner sections.
Process Window for Heavy Plastic Deformation of a Ferritic-austenitic Steel: Katharina Schwarz1; Timo Müller1; Anton Hohenwarter2; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences; 2Department of Materials Physics, University of Leoben, Austria
Duplex steels are two phase steels with nearly equal amounts of ferritic and austenitic phase. The application fields of such stainless steels are constantly increasing because of their superior resistance to corrosion and excellent combination of high strength and fracture toughness. As ultrafine-grained metals generated by severe plastic deformation have shown improved mechanical and physical properties further optimization of the coarse grained material might be realized by nano-structuring. The process window for heavy plastic deformation of this widely used steel is very narrow as martensite forms during deformation at room temperature and forms sigma phase during annealing. To avoid these mostly undesired phases various studies have been performed, as there are high pressure torsion at different temperatures and annealing combined with extensive microstructure investigations. In addition the variation of fracture toughness and ductility as a function of pre-strain is studied and compared to single phase austenitic and ferritic nano-structured materials.
Microstructure and Mechanical Properties of Nano/ultra-fine Structured High Strength Steels for High Temperature Structural Applications: Hasan Kotan1; Kris Darling2; 1Konya NEU; 2U.S. Army Research Laboratory
We report recent research in our laboratory on thermal stabilization and mechanical properties of steels of different compositions. Nano/ultra-fine structured steels with solute additions are prepared by high energy mechanical alloying of powders, consolidated by hot ECAE, studied by X-ray diffraction, focused ion beam microscopy, and transmission electron microscopy techniques and tested using room and high temperature compression tests and micro-hardness tests. The relative importance of solute additions is discussed with respect to different sample microstructures, with a range of grain, precipitate and oxide cluster sizes. It is found that the consolidated steels demonstrate an extremely high strength at room and moderately high temperatures as compared to modern day high strength steels.
Quantitative Analysis of the Precipitate Coarsening in HSLA Steels: Yiqiang Wang1; Clark Samuel2; Janik Vit2; Richard Heenan3; Kun Yan1; Sridhar Seetharaman2; Peter Lee1; 1University of Manchester; 2University of Warwick; 3ISIS Facility, Science and Technology Facilities Council
The effect of isothermal ageing time on the growth and coarsening of nano-sized vanadium precipitation in an Fe-0.047C-1.5Mn-0.2V (wt.%) alloys has been investigated by small angle neutron scattering (SANS) and electron microscopy. Quantitative analysis of the precipitation morphology, chemical composition, size, volume fraction and number density was achieved with applied a sufficient magnetic field to the samples. It was found that the V precipitates form rapidly and fit a thin disk shape prediction, reaching their largest number density within 5 minutes, consistent with the interphase precipitation formation in low carbon micro-alloyed steels. The increase in size and volume fraction of precipitates was quantified during isothermal ageing at 700°C. The bulk chemical composition of the precipitation is quite stable during the ageing, as predicted as the magnetic to nuclear scattering ratio is observed with no significant changing.
10:10 AM Break
Related Mechanisms in Athermal and Deformation-induced Martensitic Transformation in Austenitic Fe-Cr-Ni Alloys: Ye Tian1; Annika Borgenstam1; Peter Hedström1; 1KTH Royal Institute of Technology
The athermal and deformation-induced martensitic transformation in high-purity Fe-Cr-Ni alloys has been investigated. The ε-martensite (ε) was found to play a key role in the α'-martensite (α') formation. It can increase the Ms temperature for α' by affecting the nucleation behavior. For the range of Fe-Cr-Ni alloys studied, Ms temperatures for α' are almost the same as those for ε. The athermal α' tend to form along parallel ε bands and the deformation-induced martensite tend to form at both intersections of shear bands and individual shear bands and the dominating nucleation sites is goverened by the alloying content of the specific alloy. The two types of martensitic transformations are related and discussed in view of the alloys' stacking fault energies and chemical driving for martensitic transformation.
Thermodynamic-mechanical Modeling of Deformation-induced Martensitic Transformation Aided by In-situ Magnetic Measurements during Tensile Tests: Michael Hauser1; Marco Wendler1; Olena Volkova1; Javad Mola1; 1TU Bergakademie Freiberg
Austenitic Fe-Cr-Mn-Ni-based stainless steels can exhibit excellent combinations of strength and ductility by means of the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects. Due to the pronounced effect of deformation-induced martensitic transformation on the mechanical properties of such steels, it is necessary to determine the onset and the kinetics of martensitic transformation. This was done for Fe-16Cr-6Mn-6Ni-0.03N-0.03C and Fe-19Cr-3Mn-4Ni-0.15N-0.2C austenitic stainless steels by means of in-situ magnetic measurements during tensile tests at various temperatures below the deformation-induced martensite start (Mdy→α') temperature. The temperature dependence of the triggering stress for the martensitic transformation was used to calculate the mechanical energy term which, complementary to the available chemical Gibbs energy term, supplied the critical driving force for the martensitic transformation. Results indicated an anomalous stabilization of austenite against martensitic transformation at cryogenic temperatures which was attributed to the paramagnetic-to-antiferromagnetic transition of austenite in the vicinity of the Néel temperature.
Computational Design of Metastable Retained Austenite in Advanced High Strength Steels: Hao Chen1; Zhigang Yang1; Chi Zhang1; Zongbiao Dai1; 1Tsinghua University
Design of metastable retained austenite (RA) has been one of the most key issues in the development of advanced high strength steels (AHSS) as mechanical properties of AHSS are linked to the amount of RA and its stability. In the past decades, several novel concepts, e.g. Quenching & Partitioning(Q&P), Reverted austenite transformation (RAT), isothermal bainitic transformation (IBT), have been successfully proposed to obtain RA in AHSS. However, up to now, optimization of processing parameters and alloy composition in the above concepts is primarily by “trial and error” experiments or thermodynamic calculations. In this talk, we will present a physical model, in which thermodynamics and transformation kinetics are carefully considered, to design RA in AHSS. The effect of processing parameters and alloy composition in the Q&P, RAT and IBT concepts on the amount of RA and its stability will be analyzed, and a comparison among these three concepts is made.
11:30 AM Concluding Comments