High Performance Steels: Novel Steels and Extreme Environments
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
Monday 2:00 PM
March 20, 2023
Room: Aqua F
Location: Hilton
Session Chair: Kester Clarke, Colorado School of Mines; Cem Tasan, Massachusetts Institute of Technology
2:00 PM Invited
Influence of N and Mn on Performance of Advanced Austenitic Stainless Steels: Guocai Chai1; 1Alleima
For future sustainable applications, steels with high performance and low cost are demanded. Advanced austenitic stainless steels are a group of austenitic stainless steels with a nickel content near or higher 30 wt% and a pitting resistance equivalent number is near or higher than 40. In this study, N and Mn were added to replace Ni in the advanced austenitic stainless steels. Unexpectedly, a combination high Mn and N can greatly increase both strength and elongation. EBSD and ECCI studies show that this is related to an increase in amount of nano deformation twins in the steels. These phenomena have been explained by the stacking fault energy and the critical stress for deformation twinning evaluated by ab initio simulation. A combination of addition of Mn and N can also increase the critical pitting temperature, CPT. This paper will increase our understanding for the development of high performance and sustainable steels.
2:30 PM
Nano-engineering of High Performance Steels: Wenwen Song1; 1RWTH Aachen
The diversities in crystalline structure and the hierarchical features of the structures in metals lead to their distinguished deformation behaviour, elastic properties, magnetic properties, electric properties, mechanical properties, etc. In the research of metallic materials, the linkage of structure-processing-property is considered as the very important principle to understand the alloys. Following this basic principle, one can further design, select and assess suitable materials for a specific application. This research work will present several nano-engineering concepts that offer new opportunities to design and engineer the novel high performance steels into hierarchical structures with tailored properties. The multi-scale characterization (e.g. APT, TEM, in situ Synchrotron X-ray diffraction, neutron scattering, etc.) of the hierarchical features in a correlative manner from atomic scale to millimetre scale will be focused. New methods that aid controlling the process of phase transformation during deformation and/or thermal treatment in the steels will be discussed.
2:50 PM
Low-density, Medium-Mn Steels: Influence of Al Content on Microstructure Related Properties: Tomas Scuseria1; Kelcey Garza2; Dean Pierce3; Jerry Arnold2; Amy Clarke1; Kester Clarke1; 1Colorado School of Mines; 2Cleveland-Cliffs; 3Oak Ridge National Laboratory
As the steel and automotive industries accelerate sustainability efforts, novel alloy design is needed to meet targets. Low-density steels have been proposed for increased energy savings and performance for AHSS. 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 delta ferrite at hot-rolling temperatures, causing local chemical gradients and banded microstructures, in addition to altering austenite stability and deformation behavior. The influence of Al content and thermomechanical processing must be deconvoluted to establish robust alloy design strategies. Fe-Mn-Al-C alloys were produced into sheets and characterized in the cold-rolled and intercritically annealed condition for temperatures up to 900 °C and annealing times up to 6 h. Increasing Al additions were detrimental to tensile properties at fixed Mn and C, while increasing the Mn and C content at fixed Al improved specific strength.
3:10 PM
On the Development of High-strength High-damping Steels: A CALPHAD Assisted Alloy Design Study: Julian Rackwitz1; Cemal Tasan1; Gregory Olson1; 1Massachusetts Institute of Technology
Self-damping materials provide various benefits for consumer comfort and component lifetimes including noise reduction, dynamic stability, and fatigue. Lately, the Fe-Mn alloy system has gained more attention as a low-cost nonmagnetic alternative to high-damping Ti-Ni and Mn-Cu alloys. Currently, there exists a trade-off between damping capacity and strength in these alloys prohibiting their use in load-bearing applications. To overcome this limitation, we propose the need of short-range motion of partial dislocations to be sustained while impeding the long-range movement of lattice dislocations. Therefore, we present experiments to quantify the interactions between the primary damping source in Fe-Mn alloys and other microstructural features. Two prototype candidates of high-strength high-damping steels are designed based on CALPHAD modeling, prototyped, and experimentally evaluated. A driving-force-based damping model and a precipitation strengthening model are developed to derive alloy design guidelines to inform the subsequent design approach. Preliminary experimental results demonstrate the validity of this approach.
3:30 PM Break
3:50 PM
Very Strong High-entropy Steel Strengthened by Multiphase of Multiscale: Yi-Hsuan Sun1; Zen-Hao Lai1; Jui-Fan Tu2; Yu-Jen Tseng1; Hung-Wei Yen1; 1National Taiwan University; 2China Steel Corporation
High-entropy steel is Fe-based alloy designed with entropy-driven compositional complexity. In this work, a novel high-entropy lightweight steel has been developed by managing microstructural complexity under compositional complexity. In this steel, a microstructure composed of austenite and D03 intermetallic compounds is obtained by duplex annealing after cold rolling. Besides, a further aging induces precipitation of nanometer-sized κ-carbides in austenite, which bring about strength increase by 700 MPa. Interestingly, the total elongation of the steel is about 15%, which is attributed to twinning-induced plasticity. Influence of κ-carbides on stacking fault energy and deformation twin was discussed in this work. Moreover, interaction between deformation twin and κ-carbide is further investigated by TEM. The present research provides an idea in alloy and microstructural design of high-entropy lightweight steel with 1.5 GPa-level yield strength, 1.7 GPa-level ultimate tensile strength and good ductility.
4:10 PM
B2 Precipitation Strengthened Medium Mn Steel Processed by Intercitical Annealing and Aging: Jinyoung Kim1; Jinkyung Kim1; 1Hanyang University
To enhance the yield strength of the medium Mn steel, we designed Fe-Mn-C-Ni-Al medium Mn steel having the B2 phase in the microstructure due to the addition of Ni and Al. The material was subjected to casting, homogenization, hot-rolling, cold-rolling, intercritical annealing, and aging. The intercritically annealed material consists of tempered martensite and fine ferrite/austenite with the dispersed fine B2 precipitates mainly present in the BCC constituents. The microstructure after aging is similar to that after intercritical annealing. While the fraction of tempered martensite decreases, the fraction of fine ferrite/austenite increases due to the progress of recrystallization. The size of B2 precipitates increases after aging. The aged materials show higher strength and similar ductility compared to the intercritically annealed materials. We discuss the detailed microstructure-mechanical properties relationship of the investigated materials.
4:30 PM
Carbide Precipitation Strengthening Behaviour in an Additively Manufactured High-speed Steel with Unprecedented Strength: Huayue Zhang1; Hui Peng2; Hongbo Guo2; Stuart Robertson3; Paul Bagot4; Michael Moody4; Bo Chen1; 1University of Leicester; 2Beihang University; 3Loughborough University; 4University of Oxford
The carbide precipitation behaviours and resultant hardening in additively manufactured high-speed steel (HSS) were investigated with a focus on elucidating the microstructure evolution from as-built to post-processed conditions. The excellent mechanical properties with a combination of high hardness and bending strength were obtained by synergistic effects of small grains and nanoscale precipitates. The quantitive descriptions of primary carbides were characterised by SEM and FIB. The volume fraction and size distribution of nanoscale carbides were investigated by SANS. The elemental information of nano-carbides was characterised by APT. It was found that V-enriched carbides (<10 nm) precipitated at dendritic cores and Cr-enriched carbides (~40 nm) precipitated at interdendritic regions due to the heterogeneous distribution of alloying elements. This study provides important insights into the strengthening mechanism in the post-processed HSS. The knowledge gained can guide us in designing future HSS groups and developing heat treatment procedures tailored for the additive manufacturing process.
4:50 PM
Analysing the Corrosion of T91 in Liquid Lead-bismuth-Eutectic: Minyi Zhang1; Guanze He1; Mark Lapington1; Weiyue Zhou2; Michael Short2; Paul Bagot1; Felix Hofmann1; Michael Moody1; 1University of Oxford; 2Massachusetts Institute of Technology
The issue of corrosion and its dependence on irradiation remains the bottleneck in lead-bismuth-eutectic (LBE) cooled fast reactor designs. To reveal the changes occurring at the interface of lead and steel, high resolution characterisation techniques are required. We have investigated the static corrosion of T91 steel in LBE across multiple length scales using SEM/EDX, TEM, STEM, and APT. We find chromium depletion up to 10 μm away from the lead-steel interface, combined with dissolution of chromium-enriched precipitates. Furthermore, lead seems to corrode T91 grain-by-grain rather than penetrating into grain boundaries. TEM combined with EDX reveals vanadium-enriched precipitates at the T91-lead interface, suggesting that vanadium-enriched precipitates have higher resistance to corrosion than chromium-enriched precipitates. APT analysis also reveals a thin oxide layer at the T91-lead interface even under reducing conditions. Together these observations provide a rich picture of the corrosion process.