Effect of prior austenite grain morphology on hydrogen embrittlement behaviour under plastic straining in as-quenched 500 HBW steels

Prior austenite grain (PAG) structure is an important factor influencing hydrogen embrittlement (HE) susceptibility of ultrahigh-strength steels. In this study, the effect PAG shape and size on HE behaviour investigated using a novel tuning-fork testing method thermal desorption spectroscopy (TDS). Different structures were acquired via re-austenitization (860°C = A860, 960°C A960) rapid quenching as-received 500 HBW direct-quenched (DQ) steel, which has auto-tempered lath-martensitic microstructure elongated morphology. Fractography reveals different crack propagation mechanisms depending shape. With structure, hydrogen-induced transverse to PAGs was transgranular quasi-cleavage. Propagation partially intergranular with equiaxed structures, regardless size, leading equally faster fracture. The TDS results show that there are no significant differences between total contents, but re-austenitized A860 A960 steels contain higher fraction weakly trapped hydrogen. This indicates boundaries not dominant traps, rather linked geometrical structure.