High Performance Steels: High Performance Steels for Defense Applications
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 8:30 AM
March 20, 2023
Room: Aqua F
Location: Hilton

Session Chair: Krista Limmer, Army Research Laboratory; Richard Fonda, Naval Research Laboratory


8:30 AM  Invited
Designing the Precipitation Sequence in Triple Nano-precipitate Strengthened Austenitic Steel: Colin Stewart1; Richard Fonda1; Keith Knipling1; Patrick Callahan1; Paul Lambert2; 1US Naval Research Laboratory; 2US Naval Surface Warfare Center, Carderock Division
    Using integrated computational materials engineering (ICME), we have developed a novel series of FCC Austenitic steels with estimated yield strengths over 180 ksi through the formation of three nano-scale precipitate phases: (i) insoluble FCC Cu particles, (ii) ordered intermetallic NiAl precipitates, and (iii) VC precipitates. These precipitate distributions form through ageing treatments without any prior mechanical deformation. The age hardenability was evaluated by microindentation, and the precipitation sequences were assessed by atom-probe tomography across a range of ageing time steps, temperatures, and alloy compositions. This presentation will discuss the interaction mechanisms among the different precipitate phases and how those relationships change across the design space. In particular, we will also discuss leveraging this fundamental understanding of the precipitation sequences to engineer more favorable nano-scale particle distributions through modifications in the alloy composition and heat treatment, guided by ICME.

9:00 AM  
Atomistic Modeling of a Nano-precipitate Strengthened Alloy: Edwin Antillon1; Colin Stewart1; Noam Bernstein1; Michelle Johannes1; Richard Fonda1; Keith Knipling1; Patrick Callahan1; 1Naval Research Laboratory
    We present a series of atomistic level calculations for properties relevant to phase stability and strengthening mechanisms of a nano-precipitate strengthened austenitic steel alloy. Density functional theory is used to calculate bulk energies, point defects, and elastic properties of disordered and ordered phases observed in a novel nano-precipitate strengthened austenitic steel Fe–17.7Mn–10.0Ni–5.0Al–4.7Cr–4.0Cu–0.48C (wt.%). To capture short-range and long-range interactions between the precipitates and the matrix, we make use of a surrogate interatomic potentials to model interfacial properties and deformation mechanisms between the matrix and the precipitate. Our atomistic results are validated against experiment by comparing precipitate shape-morphology and quantifying the contribution of solute-solution and precipitate strengthening to the overall yield strength of the alloy

9:20 AM  
Contribution of Two Different Microstructural Morphologies on the Mechanical Responses in Medium-Mn Steels: Jeongho Han1; 1Hanyang University
    For the past decades, the steel industry has focused on the development of new generation advanced high-strength steels (AHSS) to facilitate the steel product with both excellent formability and rigid structure. Nowadays, the 3rd generation AHSS have been extensively studied for commercialization. Among the candidate alloys, the medium-Mn steels with lean alloy composition (i.e., Mn < 12 wt%, C < 0.3 wt%, etc.) have received significant attention owing to its reasonable materials cost and good mechanical responses. The corresponding steel could reveal the two-phase microstructure with plentiful retained austenite after annealing at intercritical region, leading to the high strength level and ductility. Meanwhile, according to the processing routes (e.g., hot rolling plus annealing, cold rolling plus annealing), the two different microstructural morphologies could be obtained: laminate and globular structures. In the present review, the contribution of two different microstructural morphology on the mechanical properties were systematically summarized.

9:40 AM  
High-fidelity Crystal Plasticity Finite Element Modeling of Multi-phase Medium-Mn TWIP-TRIP Steel: Considerations In Microstructure Reconstruction and Meshing for Capturing the Influences of Phase Constituents: Pengfei Shen1; Yang Liu2; Jake Benzing3; Xiang Zhang1; 1University of Wyoming; 2Imperial College London; 3National Institute of Standards and Technology
    A high-fidelity crystal plasticity finite element (CPFE) model is developed to understand the influences of phase constituents on the microstructural response in Medium-Mn steel. An automated workflow si first developed to process a set of serial Electron backscatter diffraction (EBSD) scans and stack them together for exact microstructure reconstruction is developed, followed by a meshing process to establish a high-fidelity finite element (FE) model. This FE model is then used in CPFE simulation, accounting for both twining- and transformation-induced plastic deformation. A series of microstructures are reconstructed from the same set of EBSD data with different resolutions when processing the EBSD data, and element sizes and types. Both the overall stress-strain response, as well as the local response are studied and compared, which identifies the appropriate resolution and element size needed in capturing the response in different constituents. The influence of different constituents are then studied systematically.

10:00 AM Break

10:20 AM  
Ultra-high Strength Steel for Defense Applications: Katelyn Adkison1; Stephane Forsik1; Daniel Roup1; Colleen Tomasello1; 1Carpenter Technology
    AerMet® alloys are a family of high Co-Ni secondary-hardening steels designed as a tougher replacement for 300M in defense applications. AerMet 100, 310 and 340 combine a Fe-Ni-Co lath martensite matrix and reverted austenite with fine M2C carbides to generate up to 2340 MPa (340 ksi) UTS and 38 MPa √m KIC toughness. AerMet 360, the newest addition to the family, contains more Co to further refine the martensitic matrix with a higher carbon level and Mo/Cr ratio for added precipitation strengthening. In peak hardened condition, the UTS reaches 2480 MPa (360 ksi) with 22 MPa √m KIC toughness. The relationships between structure, processing, and properties that give this family of material its unique performance will be discussed in this presentation.

10:40 AM  
Advancing AF96: Next Generation Strong/Tough Steels: Michael Rupinen1; Amy Clarke1; John Speer1; 1Colorado School of Mines
    AF9628 is a highly hardenable steel with a favorable balance of yield strength and impact toughness. While the high hardenability allows for use in large components, the effects of section size, alloying, and austenitization temperature on the microstructure and properties throughout a component are not fully characterized and understood. Large sections may experience significant differences in cooling rate during quenching leading to significant autotempering and autopartitioning in some regions. Understanding how to optimally process these steels is critical in continuing to develop strong/tough steels. Tensile and Charpy specimens were quenched in various media to simulate fast and slow cooling, representing the surface and center of large parts, for AF96 and a low Si AF96 variant. Additionally, two austenitization temperatures were studied to determine if a lower austenitization temperature might be feasible. Significant differences in the microstructural evolution and mechanical properties (especially Charpy impact energy) following quenching and tempering were observed.

11:00 AM  
Extreme Strengthening of Ausformed M54 through Ambient Temperature Rolling: Joshua Edwards1; Nicholas Derimow2; Jake Benzing2; Thomas Kozmel3; Jeffrey Lin3; Suveen Mathaudhu1; 1Colorado School of Mines; 2National Institute of Standards and Technology; 3QuesTek Innovations LLC
    Ferrium® M54® is a computationally designed medium-carbon ultra-high-strength steel (UHSS) designed for outstanding strength, toughness, and stress corrosion cracking resistance. A process involving low-percentage rolling reductions, referred to as Skin Pass Rolling (SPR), was investigated to reveal the relationships between processing, microstructure, and mechanical properties. Ambient temperature rolling to various total reductions was performed. Microstructure, feature morphology, and mechanical properties were studied through 60% cold work. Tensile strength was increased to a maximum of 2789 MPa as compared to the direct-quenched state (1916 MPa) and the ausformed + tempered state (2222 MPa). Observations from the study of ambient temperature rolled samples forecast development of highly refined microstructural features with retention of plasticity. This study has allowed us to enhance the mechanical properties of as-hardened UHSS and demonstrate a repeatable path forward for future high-specific-strength steels.

11:20 AM  
Improving the Low-temperature Toughness of Ni-Cr-Mo Low-Alloy Steel Castings via Short Intercritical Heat Treatments: Matt Frichtl1; Sreeramamurthy Ankem1; 1University of Maryland
    Intercritical heat treatments have been shown to improve the mechanical properties of many steels through a variety of mechanisms depending on the composition and processing parameters. This ongoing study is evaluating the effect of a short intercritical heat treatment near the Ac3 of HY-80 steel to further improve its low-temperature toughness. Charpy v-notch and tensile testing results will be presented showing increased impact toughness while maintaining yield strength. Synchrotron x-ray diffraction data indicates changes to the amount, morphology, and composition of the retained austenite. Coupled CALPHAD and phase-field models of solute segregation between growing proeutectoid ferrite and austenite will be discussed to provide one explanation for increased toughness from the heat treatment by stabilizing thin austenite films in the final microstructure. The results suggest that these heat treatments may be used to toughen low-alloy steels without requiring expensive alloying or processing modifications.

11:40 AM  
The Effect of Varying Carbon Equivalents on Temper Embrittlement Mechanisms in Nickel-Chromium-Molybdenum Steels: Aphrodite Strifas1; Matthew Draper2; Sreeramamurthy Ankem1; 1University of Maryland; 2Naval Surface Warfare Center - Carderock
     Ni-Cr-Mo steels with varying values of carbon equivalent were chosen to investigate the effects of resulting carbides on temper embrittlement mechanisms. Each composition was subjected to a typical industrial heat treatment followed by previously established embrittlement and recovery treatments. Microstructural features such as carbide morphologies and distribution, as well as carbide volume fraction were investigated using scanning electron microscopy and quantified using image analysis software. Mechanical characterization was completed via tensile and Charpy V-Notch testing. The influence of carbide type, composition, and distribution within the bulk and on the grain boundaries on the mechanisms of temper embrittlement will be discussed. Acknowledgement: This research is partly sponsored by the DLA-Troop Support, Philadelphia, PA and the Defense Logistics Agency Information Operations, J68, Research & Development, Ft. Belvoir, VA.