High Performance Steels: Processing - Mechanical Property Relationships II
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Jonah Klemm-Toole, Colorado School of Mines; Ana Araujo, Vesuvius USA; C. Tasan, Massachusetts Institute of Technology; Richard Fonda, Naval Research Laboratory; Amit Behera, QuesTek Innovations LLC; Benjamin Adam, Oregon State University; Krista Limmer, Devcom Army Research Laboratory; Kester Clarke, Los Alamos National Laboratory
Wednesday 2:00 PM
March 22, 2023
Room: Aqua F
Location: Hilton
Session Chair: Jonah Klemm-Toole, Colorado School of Mines; Cem Tasan, Massachusetts Institute of Technology
2:00 PM
The Relationship between Hydrogen Embrittlement Behavior and Pre-strain Level of Medium-Mn Steel: Hyuck Wook Lee1; Tak Min Park1; Hye-Jin Kim2; Jeongho Han1; 1Hanyang University; 2Hyundai-Steel Co.
Medium-Mn steels with the compositions of Fe-(3-12)Mn-(<0.3)C-xAl (wt.%) have been widely investigated during the last decades, due to their reasonable balance between material cost and mechanical properties. However, regarding the weakness of the corresponding steels, the severe hydrogen embrittlement (HE) has been considered as another challenge for the commercialization of the steels; the several reports had reported the HE resistance and H-assisted cracking behavior of the steels. The most of previous studies had focused on the medium-Mn steel prior to the deformation (i.e., as-annealed-state), and this is considered as limitation because the hydrogen atoms could be introduced to the steel during product assembling or service environment. That is, for the commercialization, the HE resistance should be investigated using the steels after deformation. In the present study, we systematically investigated the HE resistance and mechanisms of medium-Mn steels using Fe-7Mn-0.2C-3Al (wt.%) model alloys strained from 0% to 45%.
2:20 PM
Effect of Nitrogen on the Hardening Mechanisms in the Highly Deformed Steel Rex734: Manuel Koebrich1; Steffen Neumeier1; Mathias Göken1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
Nitrogen alloyed austenitic steels show an excellent trade-off between strength and ductility, as they are reaching very high yield strengths up to 2000 MPa with still sufficient ductility after heavy cold working. Additionally, nitrogen alloyed steels show a strong secondary hardening effect possibly due to elemental segregation after annealing. To understand the hardening effects and especially the role of the interstitial element nitrogen a correlative workflow has been elaborated to characterize the hardening mechanisms for the conventional nitrogen steel Rex734. Stress-strain curves were determined by miniaturized tensile tests, indicating an increased strength for the additional annealed specimen compared to the only deformed condition by Suzuki hardening. The tensile test results were then correlated to the heterogeneous local defect structure by various electron microscopy techniques. Further measurements of the local chemical composition around highly deformed areas by atom probe tomography ultimately reveal the origin of the alloy’s outstanding mechanical properties.
2:40 PM
Neighborhood Effects on Mechanically Induced Martensitic Transformation in QP Steels: Jiyun Kang1; C. Cem Tasan1; Narayan S. Pottore2; Hong Zhu2; 1Massachusetts Institute of Technology; 2ArcelorMittal
Understanding factors governing strain localization in QP steels is challenging, due to the presence of multiple phase constituents including metastable retained austenite. Microscopic strain partitioning among such phases is considered critical in the stability of retained austenite, which often competes with elemental partitioning effects. In this work, we integrate in situ SEM/EBSD and synchrotron XRD tensile tests to reveal the neighborhood effects on mechanically induced martensitic transformation. Our results demonstrate that local strain partitioning effects can exceed the elemental partitioning effects, highlighting the role of ferrite in controlling the transformation. Based on our findings, microstructure design strategies to improve strain hardenability of this steel will be provided.
3:00 PM
Residual Stresses Near Inclusion Caused by Martensite Transformation: Tom Andersson1; Matti Lindroos1; Anssi Laukkanen1; Tomi Suhonen1; Joona Vaara2; Tero Frondelius2; 1VTT; 2Wärtsilä
Fatigue lifetime of metals is often the limiting factor for different machines and components in various applications subjected to cyclic loading. In martensitic steels, a non-metallic inclusion is often found at the crack initiation site. The interplay between the inclusion, surrounding steel, and the interface between them is not fully understood and often the largest inclusion, assumed to be the worst defect, is not found to be the one initiated the crack that caused the final failure.In this work, we model the formation of residual stresses, caused by the cooling and martensitic transformation near the inclusion using crystal plasticity finite element model. In the model elastic, dislocation driven plastic contribution, thermal, and inelastic deformation related phase transformation are taken into account using small deformation framework. Slip occurring both in parent austenite at elevated temperature and in child martensite at lower temperatures is taken into account.
3:20 PM
Exceptional Fatigue Performance of Si and V Alloyed Nitriding Steels: Jonah Klemm-Toole1; Michael Burnett1; Kip Findley1; 1Colorado School of Mines
The useful life of many structural machine components is limited by fatigue. Thermochemical surface treatments such as nitriding improve fatigue performance by increasing surface hardness as well as inducing compressive residual stress. The increase of surface hardness and compressive residual stress is associated with the precipitation of fine nitride phases in the nitrided surface. In this work, we show that alloying a medium carbon steel with Si and V drastically improves the fatigue performance by the combination of increasing the surface properties (hardness and compressive residual stress) as well as increasing the base metal strength after nitriding. Quantitative transmission electron microscopy is used to relate Si and V content to the size and volume fraction of nitride precipitates to the property improvements. Opportunities for future alloy design strategies for nitriding steels are discussed.
3:40 PM Break
3:55 PM Cancelled
Yielding Behavior of Triplex Medium Mn Steel Alternated with Cooling Strategies: Altering Martensite/Ferrite Interfacial Feature: Xiao Shen1; Bin Hu2; Qinyi Guo2; Haiwen Luo2; Wenwen Song1; 1RWTH Aachen University; 2University of Science and Technology Beijing
The growing demands for weight saving, emission reduction and passenger safety in the automotive industry have promoted new concepts for medium-Mn steels (MMnS) design to achieve an excellent combination of high strength and superior ductility. In the present work, we reported the influence of cooling processes (air cooling versus water quenching) on the yielding behaviors of a medium Mn steel with nanostructured triplex austenite + ferrite + martensite microstructure. Multiscale characterization tools (synchrotron X-ray diffraction, EBSD, TEM and APT) were used in combination with DICTRA simulation to understand the microstructural evolution and interactions between GNDs with segregated interfaces. This study provides an effective alternative to suppress the discontinuous yielding in designing high-performance nanocrystalline MMS. The understanding of the microstructure-property relationship is extended to the nanoscale in MMS.
4:15 PM
Deformation and Damage Evolution of AHSS in Uniaxial Tension and Plane Strain Bending: Nizia Mendes Fonseca1; David Wilkinson1; Jidong Kang2; 1McMaster University; 2CanmetMATERIALS
AHSS show reduced ductility during local formability operations such as tight-radius bending and edge stretching, which is not predicted by the tensile elongation. Therefore, it is crucial to understand how the microstructure of AHSS affects their behaviour in tension and tight-radius bending. A DP and a Q&P steel were investigated in this project. The strain distribution at the sub-grain level and the damage micromechanisms were assessed through quasi in-situ SEM tensile and bend testing. X-ray computed micro-tomography (µ-XCT) was employed to measure the three-dimensional damage development quantitatively. Results show that damage nucleation and evolution are delayed in the Q&P steel compared to the DP steel. The improved behaviour of the Q&P980 steel can be attributed to the TRIP effect and the mechanical compatibility between the microstructural constituents.
4:35 PM
Modeling the Tensile Behavior of Martensitic Low-alloy Steels Accounting of Microstructural Heterogeneities: Juan Macchi1; Guillaume Geandier1; Julien Teixeira1; Sabine Denis1; Frédéric Bonnet2; Sébastien Allain1; 1Institut Jean Lamour Ijl (Cnrs Umr7198); 2ArcelorMittal Research SA
Martensite is a key component of advanced high strength steels and the main constituent of pressed hardened steels. This phase is formed upon cooling from the austenite by a displacive sequential transformation inducing heterogeneities of local dislocation densities, domain sizes, C segregation/precipitations states and internal stresses. In this work, those microstructural distributions have been characterized by in situ High Energy XRD experiments for determining the distribution of dislocation densities and by EBSD analysis for the domain sizes in three low-carbon martensitic steels. By considering the local recovery kinetics, the internal stresses relaxation as well as by coupling a new developed and calibrated precipitation model, we developed micromechanical model which is able to predict the tensile behavior of as-quenched as well as tempered states for low-carbon (between 0.1 and 0.3 wt.%C) martensitic steels.
4:55 PM
Phase Boundary Segregation Induced Strengthening in Ultrafine-grained Duplex Medium-Mn Steels: Yan Ma1; Binhan Sun2; Alexander Schökel3; Wenwen Song4; Dirk Ponge2; Dierk Raabe2; Wolfgang Bleck4; 1Max-Planck-Institut für Eisenforschung; RWTH Aachen University; 2Max-Planck-Institut für Eisenforschung; 3Deutsches Elektronen-Synchrotron DESY; 4RWTH Aachen University
Hetero-interfaces affect the materials in various aspects such as dislocation activity and damage formation. However, it remains a question whether the characteristics of phase boundaries would also have an impact on the mechanical behavior in multiphase steels. Here we reveal a phase boundary segregation-induced strengthening effect in ultrafine-grained duplex medium-Mn steels. We found that the carbon segregation at ferrite-austenite phase boundaries resulted in a yield strength enhancement by 100–120 MPa and simultaneously promoted discontinuous yielding. The sharp carbon segregation at the phase boundaries impeded interfacial dislocation emission, thus increasing the stress required to activate such dislocation nucleation process and initiate plastic deformation. These findings extend the current understanding of the yielding behavior in medium-Mn steels, and more importantly, shed light on utilizing and manipulating phase boundary segregation to improve the mechanical performance of multiphase metallic materials.