The impact of Nb, Ti, Zr, B, V, and mo on the hydrogen diffusion in four different AHSS/UHSS microstructures

Advanced and ultra-high strength steels (AHSS/UHSS) are susceptible to hydrogen embrittlement (HE), for which diffusion of hydrogen is essential. To obtain information on hydrogen diffusion in AHSS grades, the present work is focusing on the impact of AHSS grade microstructures and microalloying elements (Nb, Ti, Zr, V, B, and Mo) on the hydrogen diffusion coefficient and the density and energy of reversible traps. For this purpose hydrogen diffusion in non-and microalloyed dual-phase-, complex-phase, and tempered martensitic microstructures with tensile strength levels between 1200 and 1400 MPa was analyzed. The diffusion coefficient and trapping parameters were determined via electrochemical permeation measurements according to the works of Grabke et al. and Gehrmann. Generally, a dependence of the hydrogen diffusion coefficient on the microstructure was found with tempered martensitic microstructures showing the highest diffusion coefficents followed by dual-phase microstructures. Complex-phase microstructures reveal the lowest values for the diffusion coefficient. A significant dependence of the diffusion coefficient and trapping parameters on microalloying is not evident, except for substitutionally dissolved Mo and V-precipitates which tend to influence the density of reversible traps significantly. In this work hydrogen diffusion in four non-and microalloyed AHSS/UHSS grades was investigated. The results indicate that hydrogen diffusion depends significantly on the microstructure adjusted. The tempered martensitic grade shows the highest diffusivity, followed by the dual-phase steel. Complex-phase steel grades reveal the lowest diffusivity. However, precipitates and substitutional atoms of microalloying elements seem to have a negligible effect on hydrogen diffusion.