Review on Hydrogen Embrittlement of Press-hardened Steels for Automotive Applications

Press-hardened steel (PHS) with an ultimate tensile strength (UTS) of 1500 MPa has been widely used in automotive body-in-white in the last two decades, due to its ultra-high strength and excellent formability that is achieved by hot stamping process. However, the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement. To reduce this kind of risk, recent research efforts have been focused on various ways to optimize the microstructure of PHS. The present review intends to summarize these efforts, to highlight present solutions to address hydrogen embrittlement, and to shed light on directions for future improvement. The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition. The substrate part covers the influence of martensite, carbides, inclusions, and retained austenite, while the surface part covers decarburization and oxidation, pre-coating, and trimming.