Control of retained austenite stability during the heat treatment of the high performance steel Ferrium® M54®

Ferrium® M54® ultra-high-strength steel is an excellent candidate for landing gear applications due to its balance of UTS, KIC, and KISCC properties, which is among the best compared to steels currently in use. The tensile strength of Ferrium® M54® at room temperature is mainly provided by the martensitic structure formed during quenching and by the precipitation of molybdenum M 2 C carbides during tempering. However, a significant amount of retained austenite may remain after heat treatment. This study demonstrates that both the temperature and the delay between quenching and cryogenic treatment are critical parameters. Specifically, carbon diffusion during this period, even at room temperature, contributes to stabilizing the retained austenite. Austenite stabilization is modelled using the Johnson-Mehl-Avrami-Kolmogorov law to determine the maximum allowable dwell time between quenching and cryogenic treatment. This important finding helps in stabilizing the yield strength and preventing the transformation of retained austenite into fresh martensite under load.