Consideration of hydrogen transport in press-hardened 22MnB5

Abstract

Abstract The increasing use of hot stamped high strength steels like 22MnB5 (1.5528) for complex crash relevant structural components in the vehicle body, and the problem of hydrogen-assisted damage have gained increasing importance in the automotive industry. In the high strength category, hot stamped quenched and tempered steels (tensile strength up to 1600 MPa) are under unfavorable conditions for potential risk of hydrogen embrittlement, e. g., at elevated hydrogen input, in the presence of increased tensions, and in the further processing of these steels. Peculiarities of boron-alloyed quenched and tempered steel are coating systems that are applied to the steel substrate prior to hot stamping and they serve as a protection against scaling during austenitization. These coating systems, aluminum-silicon (+AS150) and zinc (+Z140) which are most commonly used, have significant influence on the diffusion and desorption of diffusible hydrogen in thin 22MnB5 sheets. The investigations of the hydrogen transport described in this paper are carried out by thermal desorption analysis (TDA). This measurement method allows the determination of activation energies and pre-exponential diffusion coefficients of hydrogen for the different coating variants of 22MnB5 by different temperature regimes (heating rates). Furthermore, the corresponding diffusion coefficients of the studied states are determined. Based on these results, an estimate of desorption is carried out, and then empirically tested by isothermal analyzes.