Enhanced lattice defect formation associated with hydrogen and hydrogen embrittlement under elastic stress of a tempered martensitic steel

Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Oshima, Nagayasu*; Hirade, Tetsuya  

Hydrogen behavior and hydrogen-enhanced lattice defect formation under elastic stress of tempered martensitic steel were clarified with respect to dislocations and vacancies by thermal desorption analysis (TDA) using hydrogen as a probe of defects and a positron probe microanalyzer (PPMA). The relationship between hydrogen embrittlement and lattice defects associated with hydrogen was also investigated. The amount of lattice defects increased gradually with increasing time of applied stress. The specimen fractured under elastic stress. The enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss. Even though hydrogen was completely removed by degassing the vacancies remain. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.