Vacancy Clustering Behavior in Low Alloy Martensitic Steel during Tensile Deformation with Hydrogen Charging

Abstract

The effects of hydrogen charge on the formation of vacancy-type defects in low alloy martensitic steel were investigated by using positron lifetime spectroscopy. During slow strain rate tensile tests (SSRT), dislocation and vacancy were introduced and increased with increasing tensile strains. Vacancy clustering was significantly promoted by hydrogen charge, although there was no remarkable difference in the dislocation density and mono-vacancy equivalent vacancy density between hydrogen-charged and uncharged samples under the same tensile strains. Increase in hydrogen concentration in the steel promoted vacancy clustering. Preferential conditions for the vacancy clustering showed a good agreement with the conditions for significant elongation loss by SSRT, implying the vacancy clustering has an big effect on hydrogen embrittlement. In the case of constant load tests under applied stress in elastic region, no increase in vacancy and dislocation density was observed. This implies plastic deformation is necessary for the formation of vacancy-type defects even under hydrogen charging.