FEATURE ADVANCED MATERIALS & PROCESSES | APRIL 2025 50 I n 2022, the School of Materials Engineering at Purdue University launched the Purdue Heat Treating Consor- tium (PHTC) with the aim of performing basic, pre- competitive research and applying it to industrial practices. This initiative benefits both its members and the broader heat treating community by providing critical in-depth analysis of heat-treating-related problems and development of new heat treating technologies. As of 2025, the PHTC is supported by 13 industry members, including OEMs, furnace manufacturers, and metal product manufacturers that serve industries such as transportation, defense, and agriculture, as shown in Fig. 1. Over the past three years, the consortium has supported seven M.S./Ph.D.-level projects and has already seen tangible successes in transitioning technologies. These include new sustainable and environmentally friendly austempering oils and processes, as well as life- cycle analysis of carburization heat treatments. NEW AUSTEMPERING PROCESSES AND OILS Austempering of carbon steels requires fast quenching to just above the martensite start temperature, followed by extended holding times of 30 min to 5 hr to form a lower bainitic microstructure. Such austempered steels can exhibit improved toughness and ductility while maintaining high strength with the potential for improved hydrogen embrittlement resistance. Current industrial practices OVERVIEW OF THE PURDUE HEAT TREATING CONSORTIUM The Purdue Heat Treating Consortium works to advance the science of heat treating by turning new technologies into practice. Michael S. Titus,* Sarvesh Baja, David Johnson, Matthew Krane, Kenneth Sandhage, Lakshmi Srinivasan, Jeffrey Youngblood, and Fu Zhao Purdue Heat Treating Consortium, Purdue University, West Lafayette, Indiana typically utilize molten salts, usually composed of nitrate solutions that can be difficult to wash, clean, and transport, and which require special handling and disposal procedures. Two recent efforts at PHTC, led by a team of materials engineering faculty (David Johnson, Kenneth Sandhage, Matthew Krane, Jeff Youngblood, and Michael Titus), developed an austempering process using high-boiling point and high-degradation point sustainable oils. Early results in a carburized 4120 steel showed superior quench properties in the sustainable oil compared to commercially available petroleum-based products. The resulting carburized and austempered microstructures exhibited a lower bainite case and tempered lath martensite core (Fig. 2). Due to enhanced volumetric expansion in the case, the measured residual stress was found to be compressive, indicating that large components can be quenched without significant distortion and quench cracking while maintaining many desirable properties such as toughness, hardness, and strength. PHTC is currently working with industry members to scale up and transition the technology for more widespread use. *Member of ASM International Fig. 1 — Map and list of industry members supporting PHTC. Fig. 2 — Carburized and austempered 4120 steel, showing (a) case region with lower bainitic microstructure and (b) core region with tempered lath martensite. (b) (a) 6
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