Effects of austenitizing time on microstructure and hydrogen environment-assisted cracking behavior of M54 steel

Ferrium M54 steel offers a cost-effective alternative to AerMet 100, achieving comparable strength and toughness through reduced Co content and additions of W, Nb, and Ti. However, hydrogen environment-assisted cracking (HEAC) is a critical concern for the engineering application of this steel. This study investigated the effect of austenitizing time on the microstructure and HEAC behavior of M54 steel. Microstructure analyses through optical microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy revealed that extending austenitizing time beyond 75 min led to noticeable grain growth, dissolution of MC carbides and a reduction of the austenite volume fraction. The prior austenite grain boundaries acted as the preferential pathway for hydrogen atoms to diffuse in M54 steel. The hydrogen diffusion coefficient, crack growth rate and HEAC susceptibility exhibited a peak value after austenitizing treatment for 75 min, which may be due to the combined effect of the austenite fraction and prior austenite grain size. This work elucidates how a specific austenitizing treatment can reduce HEAC risks and proposes an optimized austenitizing protocol for M54 steel.