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Press-hardened steel (PHS), used for automotive safety-related structure parts, is sensitive to hydrogen embrittlement due to its martensitic microstructure. Hydrogen is introduced in PHS during the hot press forming (HPF) process, by an atmospheric corrosion process. In this study, the hydrogen embrittlement behavior of uncoated, aluminized, and galvanized PHSs was investigated. The Al-10%Si coating promoted the absorption of diffusible hydrogen at elevated temperature during the HPF while the reacted coating layer prevented the absorbed hydrogen from out-diffusing through the reacted coating surface layer at room temperature. Therefore, the aluminized PHS showed a greater sensitivity to both the hydrogen uptake and the resultant embrittlement, as compared to the uncoated and galvanized PHSs. Use of galvanized PHS for HPF application reduces the risk of hydrogen embrittlement, since the Zn coating effectively prevents the hydrogen uptake. The greater embrittlement resistance of the galvanized PHS is possibly due to the inhibition of the hydrogen generation reaction by the surface ZnO oxide layer and the low rate of hydrogen transport through the liquid Zn phase.

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Internal friction (IF) measurements were carried out on a press hardened steel (PHS) after continuous annealing, press hardening and bake hardening. The IF peaks of the PHS with a lath martensite microstructure were analysed by comparison with previously published data. This was supplemented by comparison with the IF spectra of the same steel with a ferrite–pearlite microstructure after deformation at room temperature, and after recrystallisation annealing and quenching. The relation between the IF peaks of PHS, and the γ-peak, Snoek peak and Snoek-Kê-Köster peak observed for ferritic steel is discussed.