Improving the Hydrogen Embrittlement Property of 1.8 GPa Press-Hardened Steel by Controlling the Prior Austenite Grain Size

Abstract

Press-hardened steel (PHS) with a tensile strength of 1.8 GPa exhibits significant potential for lightweight applications in automobile industry. Nevertheless, H embrittlement (HE) remains a serious concern in the practical applications of PHS. Nb alloying can improve the HE property of PHS by introducing extensive nanosized niobium carbides (10–20 nm in diameter), which are irreversible H traps in the steel matrix, into PHS. Interestingly, herein, we discovered that even without the formation of a large amount of nanosized niobium carbides, Nb alloying was beneficial for improving the HE property of a 1.8 GPa press-hardened PHS. The addition of Nb to this PHS resulted in complex submicron-sized (Nb,Ti)(C,N) precipitates rather than nanosized NbC precipitates. These submicron-sized (Nb,Ti)(C,N) precipitates effectively refined the prior austenite grain (PAG) size, leading to a higher density of low-angle grain boundaries, which reduced the H diffusion rate and also acted as H traps. Consequently, the average amount of H at the PAG boundary was substantially low, thereby improving the resistance to HE.