Microstructural and Crystallographic Features of Hydrogen-related Crack Propagation in Low Carbon Martensitic Steel

This study investigated the characteristics of hydrogen-related crack propagation in low carbon lath martensite steel through orientation analysis using electron backscattering diffraction. The orientation analysis revealed that the hydrogen-related fracture surface consisted of the {011}(m) facets, which were also parallel to the block boundaries or lath boundaries in the lath martensite structure. In addition, micro-cracks were observed on or in the vicinity of the prior austenite grain boundaries. On the basis of the experimental results, we proposed that hydrogen enhanced local plastic deformation occurred in the vicinity of prior austenite grain boundaries. The mechanism of hydrogen-related fracture is characterized by the formation of micro-cracks around prior austenite grain boundaries and subsequent crack propagation along block boundaries or lath boundaries.