Advanced High Strength Steels V: Session III
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Ana Araujo, Vesuvius USA; Louis Hector, General Motors Global Technical Center; Igor Vieira, Nucor Steel; Lijia Zhao, ArcelorMittal USA; Krista Limmer, Devcom Army Research Laboratory; Jonah Klemm-Toole, Colorado School of Mines; Sebastien Allain, Institut Jean Lamour; MingXin Huang, University of Hong Kong
Tuesday 8:30 AM
March 16, 2021
Room: RM 6
Location: TMS2021 Virtual
8:30 AM
A Spatial Spin Average Approach to Model Austenitic Steels Using First Principle Calculations: Edwin Antillon1; Michelle Johannes1; Noam Bernstein1; 1Naval Research Lab
We use first principle calculations to model austenitic stainless steel alloys. Modeling paramagnetic disordered alloys remains a challenge using ab-initio calculations due to the effect that finite-temperature magnetic excitations have on the stability of austenitic steels. A super-cell approach is used to approximate disordered magnetic moments using spatial spin averaging from several static zero temperature calculations. We demonstrate this approach on point defects (Mn,Mo,C) on 316 Steels, and populate a Labusch model that takes into account the role of paramagnetism in solid solution hardening of austenitic steels.
8:50 AM
Phase Evolution of Triple Nano-precipitate Strengthened Mn-stabilized Austenitic Steel: Colin Stewart1; Richard Fonda2; Keith Knipling2; Patrick Callahan2; 1National Research Council Associate at the U.S. Naval Research Laboratory; 2U.S. Naval Research Laboratory
Precipitation of nano-scale phases upon ageing is a desireable strengthening mechanism in FCC austenitic steels due to the lack of significant solid solution strengthening. An ICME approach has been used to engineer a cost-effective Mn-stabilized austenitic steel that demonstrates precipitation of three nano-scale phases: (i) insoluble Cu (FCC) particles; (ii) ordered intermetallic β-NiAl (B2) precipitates; and (iii) carbides. Atom probe tomography (APT) in combination with transmission electron microscopy (TEM) have been used to assess the evolution of precipitate composition, morphology, and distribution over a variety of ageing times. This characterization is used to determine the potential mechanisms of particle formation, and can be used to refine computational models for an efficient ICME alloy design approach.
9:10 AM
Microstructural Refinement and Homogenization of High Strength Austenitic Steels for Lightweighting Using Equal Channel Angular Pressing: Ibrahim Karaman1; Matthew Vaughan1; Sezer Picak1; 1Texas A&M University
Fe-Mn-Al-C steels are lightweight alloys that offer great potential as high specific strength materials for weight critical applications. The goal of the current work is to subject Fe-Mn-Al-C to severe plastic deformation via equal channel angular pressing in an effort to explore the strengthening potential of both grain refinement and precipitation hardening in these steels. Precipitation hardening is the method of choice for increasing the strength levels of Fe-Mn-Al-C steels. However, the precipitate distribution in the microstructure is not always homogeneous. In this study, the effect of grain refinement as an additional strengthening mechanism and the role of grain refinement with high dislocation density on the precipitation kinetics and the distribution have been studied for these steels. We have shown that the presence of micro-segregation of Mn have a strong influence on the mechanical properties of Fe-Mn-Al-C steels. ECAP improves the compositional homogeneity and precipitate distribution, leading to higher strengths.
9:30 AM
Role of Metal Carbides in the Formation of Austenite in a High-Ni Martensitic Steel: Chia-Pao Lee1; Amir Farkoosh1; Paul Lambert2; David Seidman1; 1Northwestern University; 2Carderock Division, Naval Surface Warfare Center
Low-carbon 10 wt.% Ni steels with an appropriate quench-lamellarization-tempering (QLT) heat treatment achieve an excellent combination of high-strength, high-toughness, and projectile ballistic resistance due to a high-volume fraction of thermally stable retained austenite. Research has demonstrated that core-shell MC/M2C carbides (M is Mo, Cr, V) form during the QLT treatment. It is unknown whether these metal carbides play any significant role in austenite formation. We have designed a heat treatment that forms carbides with different sizes and distributions, within a martensitic matrix prior to the lamellarization step, which permits studying the role of carbides in austenite formation and possibly altering the size and distribution of austenite grains, to further improve the mechanical properties of this steel. Herein, we utilize experimental characterization techniques, scanning electron-microscopy, synchrotron x-ray diffraction, atom-probe tomography, and electron backscatter diffraction, to follow the kinetics of phase transformations and the resulting microstructural features at different hierarchical length-scales.
9:50 AM
Effects of Cold Rolling on Austenite Formation in a QLT-Treated High-Ni Martensitic Steel: Chia-Pao Lee1; Amir Farkoosh1; Paul Lambert2; David Seidman1; 1Northwestern University; 2Carderock Division, Naval Surface Warfare Center
Low-carbon 10 wt.% Ni steels are processed through an intercritical quench-lamellarizing-tempering (QLT) treatment to form a fine dispersion of thermally-stable austenite in a martensitic matrix. Our investigations reveal that the austenite phase nucleates on crystallographic defects, such as martensite lath boundaries, grain boundaries, dislocations, and stacking faults. Thus, we hypothesize that it is possible to increase the number density and volume fraction of the retained austenite grains by increasing the existing crystallographic defects within the microstructure between the QLT treatment steps. In this study, we introduced a cold-rolling step (~10-30% plastic deformation) between the Q- and L-steps, with the purpose of increasing the dislocation density and other defects before austenite reversion. The microstructures developed after this thermomechanical treatment are studied utilizing synchrotron x-ray diffraction, atom-probe tomography, and electron backscatter diffraction analyses. Tensile and Charpy impact tests are conducted to evaluate the mechanical properties at ambient and cryogenic temperatures.
10:10 AM
Twinning-induced Plasticity of Austenitic Lightweight High-entropy Steel: Hung-Wei Yen1; Zen-Hao Lai1; Yi-Hsuan Sun1; Yi-Ting Lin1; Jui-Fan Tu2; 1National Taiwan University; 2China Steel Corporation
The current work investigated mechanical behaviors of a novel austenitic lightweight steel which combined the originally contradictory two systems, lightweight steel and TWIP steel, by compositional complexity. This steel initially deformed via planar gliding of perfect dislocation, followed by slip of partial dislocations and deformation twin though its stacking fault energy is actually high. Moreover, the Hall-Petch constant of this steel is over 600 MPaμm-1/2, indicating a very effective strengthening by grain refinement. Combined with microband-induced plasticity and twinning-induced plasticity, this austenitic lightweight steel reached its yield strength of 400-500 MPa, ultimate tensile strength of 800-950 MPa, and total elongation of about 70%.