High Performance Steels: Microstructure Evolution in Steels
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Ana Luiza Araujo, CBMM North America Inc.; C. Tasan, Massachusetts Institute of Technology; Jonah Kleem-Toole, Colorado School of Mines; Louis Hector, General Motors Global Technical Center; Tilmann Hickel, Max-Planck-Institut Fuer Eisenforschung; Benjamin Adam, Oregon State University

Thursday 2:00 PM
March 3, 2022
Room: 252C
Location: Anaheim Convention Center

Session Chair: Jonah Klemm-Toole, Colorado School of Mines; Benjamin Adam, Portland State University

2:00 PM  
NOW ON-DEMAND ONLY – Co-optimization of Mechanical, Thermal, and Oxidation Properties in Steels for Energy Conversion Systems: Dean Pierce1; Govindarajan Muralidharan1; Artem Trofimov1; Hsin Wang1; Michael Tess2; Katie Sebeck2; Eric Gingrich2; Gerald. Byrd2; Allen Haynes1; 1Oak Ridge National Laboratory; 2Ground Vehicles Systems Center
    High temperature steels for energy conversion systems like internal combustion engines and heat exchangers can achieve improved performance through optimization of numerous properties, such as strength, thermal conductivity, and oxidation resistance. The aforementioned properties are often in conflict, where improving one negatively influences others, resulting in well known metallurgical tradeoffs. This research investigates how composition, phase equilibria, and microstructure can be optimized to partially overcome these tradeoffs.

2:20 PM  
Loading/Unloading Yielding Behavior in 304 Stainless Steel: Melissa Thrun1; Christopher Finfrock1; Amy Clarke1; Kester Clarke1; 1Colorado School of Mines
    To make useful parts, forming operations have become increasingly complex, many of which include loading and unloading, bending and unbending, and a variety of different strain states and strain rates. One important factor in forming useful parts is the yield and flow stresses of the material, which ultimately dictate the loads and equipment required to make the part. In this study, interrupted testing of 304 stainless steel was performed to observe the effects of unloading, fully and partially, as well as differing the time between unloading and loading, on subsequent deformation. Upon reloading in all conditions, an increase in yield stress was observed. The magnitude of the increase varied both with time between unloading and reloading, and partial and full unload. The appearance of this yield point phenomena is attributed to strain aging and dislocation trapping mechanisms active in the matrix and presents a potential challenge for forming TRIP-aided materials.

2:40 PM  
Low-density Steels: Influence of Al Content and Processing on Microstructure and Properties in Medium-Mn Steels: Tomas Scuseria1; Kelcey Garza2; Dean Pierce3; Amrinder Gill2; Jerry Arnold2; Amy Clarke1; Kester Clarke1; 1Colorado School of Mines; 2Cleveland-Cliffs Inc.; 3Oak Ridge National Laboratory
    Low-density steels have been proposed as a candidate for increased energy savings and performance for Advanced High Strength Steel (AHSS) in the automotive industry. High Al additions (4-11 wt%) to medium-Mn steels provide mass savings through density reductions, while promoting duplex, ferrite-austenite microstructures with excellent strength-elongation combinations. Concurrently, Al additions stabilize ferrite at hot-rolling temperatures, creating local chemical gradients, in addition to altering austenite stability and work-hardening characteristics, such as Transformation Induced Plasticity (TRIP), Twinning Induced Plasticity (TWIP), or planar slip. The influence of Al additions and processing on microstructure and mechanical properties must be deconvoluted to establish robust alloy design strategies. Experimental Fe-Mn-Al-C based grades with Si and Cr additions were produced into sheets and characterized in the hot-rolled and intercritically annealed conditions. The phase evolution and deformation behavior of duplex microstructures were investigated through dilatometry, tensile testing, and in-situ straining stage with SEM.

3:00 PM  
On the Phase Stability, Mechanical Properties, and Deformation Mechanisms of an Equiatomic CrFeNi Medium-entropy Alloy: Mike Schneider1; Guillaume Laplanche1; 1Ruhr-University Bochum
    The CrFeNi medium-entropy alloy, due to its compositional simplicity and its single phase character, constitutes a missing link between binary and more complex engineering alloys such as austenitic stainless steels and Fe-based superalloys. In this study, heat treatments at various temperatures revealed that CrFeNi forms a stable FCC solid solution above ~1250 K. Compression and tensile tests were carried out for recrystallized FCC microstructures with different grain sizes between 77 K and 873 K. To reveal the active deformation mechanisms in CrFeNi, additional tensile tests were interrupted at different strains followed by transmission electron microscopy analyses. In all cases, deformation was accommodated by dislocation glide at low strains, whereas twinning was additionally triggered above a critical resolved shear stress. From these findings, the critical resolved shear stress for twinning in CrFeNi was determined to be roughly temperature independent and in good accordance with modeling predictions.

3:20 PM Break

3:35 PM  
Non-metallic Precipitates Evolution Mechanism of Fe-3.0wt%Si Steel: Huilan Sun1; Zimo Bi1; Di Zhang1; Zhihong Guo1; Bo Wang1; 1Hebei University of Science and Technology
    The non-metallic precipitation formation and transformation mechanism of non-oriented electrical steel have been studied when the heating treatment temperature ranges from 1000C-1240C. The types, morphologies, and sizes of precipitates were analyzed by the methods of FESEM and EDS. The results show that the main precipitate of non-oriented electrical steel is AlN, as well as some sulfides and composite precipitates. It shows a density gradient of precipitates along the thickness direction. The precipitates mainly distribute in the crystal grains, which have spherical, rod-like, and irregular shapes. When the heating temperature lower than 1120C, the precipitates aggregate and coarsen. As the temperature increases to 1200C, the number of precipitates gradually increases.