Improving hydrogen embrittlement resistance of a modified press hardening steel by introducing retained austenite as hydrogen trap

The effect of retained austenite (RA) with higher mechanical stability on hydrogen embrittlement resistance of a modified 22MnB5 (C 0.22, Si 0.8, Mn 1.5, B 0.002, Fe balance, in wt.%) press hardening steel (PHS) has been studied. One-step quenching and partitioning (Q&P) treatment was applied to PHS, and around 6 vol.% ultra-fine RA was obtained. The ultra-fine RA was found to act as stronger hydrogen trap than dislocations and grain boundaries in martensitic matrix and can decrease the apparent diffusion coefficient of hydrogen from 5.97 9 10–7 to 3.83 9 10–7 cm2 s-1, which was verified by the combination of thermal desorption spectroscopy analysis and hydrogen permeation test. The higher mechanical stability of the ultrafine RA assures enough stability of the hydrogen trap, which results in better hydrogen embrittlement resistance in Q&P-treated PHS than the conventional directly quenched PHS.