Abstract
In this study, we attempted to elucidate the hydrogen embrittlement mechanism in lath martensite steels by multiscale approach across fracture test, microbeam analysis and atomic simulation. It was confirmed that the microcracks initiated not only along prior austenite grain boundaries but also partially along the boundaries existing within the prior austenite grain. To compare hydrogen embrittlement risk on various boundaries, the modelling method was developed to reflect the crystallography on hierarchical lath martensite microstructure. Hydrogen trapping on the boundaries was analysed using molecular dynamics calculations using neural network interatomic potential. Consequently, it was clarified that the hydrogen trapping energy of prior austenite grain boundaries is higher than that of the block and sub-block boundaries. Thus, the initiation risk due to hydrogen was lower in the block and sub-block boundaries which are the boundaries within prior austenite grain. It was suggested that elementary processes of hydrogen-induced isolated microcracks with length of approximately 30~50 μm are the crack initiation on intergranular boundaries with high risk and crack growth along intragranular boundaries with middle risk due to weaker hydrogen trapping.
