Modeling alloy carbide formation and coarsening during high-temperature tempering of Ferrium C64 steel

High-alloy steels, like Ferrium C64, are used in powertrain components due to their corrosion resistance and strength at high-temperatures. These steels are tempered at temperatures above traditional steels. During tempering, alloy elements combine with carbon to form fine alloy carbides that increase the steel’s hardness and mechanical performance. In the early stages of tempering, softening occurs due to carbon exiting quenched martensite, then hardening as the alloy carbides form. At longer tempering times, the alloy carbides coarsen and ripen, thus softening the steel. A predictive material model for the high-tempering response of steels can ensure peak hardening properties are met. To accurately model the heat treatment process, austenitization rates and thermal expansion during heating, carbon diffusion and saturation limits for carburization, phase transformation rates and thermal contraction rates per phase during cooling and quenching, deep-freeze kinetics for retained austenite reduction, tempering kinetics for tempered martensite formation, and carbide kinetics for formation and growth must be considered. Additionally, mechanical properties per phase and carbon level must be developed to ensure proper mechanical response in the model. Once developed, the material model can be used to design and optimize the high-temperature tempering process for any process using these high alloy steels.