Effect of Strain Rate on Hydrogen Embrittlement Susceptibility of Tempered Martensitic Steel and the Rate-Determining Process

Abstract

The effect of strain rate on hydrogen embrittlement susceptibility of high strength tempered martensitic steel was investigated by tensile tests under cathodic hydrogen charge. Fracture elongation was decreased with a decrease in strain rate and increase in diffusible hydrogen concentration. The mechanism of hydrogen embrittlement susceptibility was investigated based on vacancy-type lattice defects formation by positron lifetime spectroscopy. The clear correlation was not comfirmed between strain rate and the parameters of average positron lifetime, dislocation density and vacancy density. These parameters decreased with a decrease in fracture elongation, it means that these parameters did not reflect hydrogen embrittlement susceptibility. On the other hand, vacancy clustering was promoted with a decrease in strain rate. Therefore, it is assumed that strain rate dependence of hydrogen embrittlement susceptibility is determined by vacancy clustering process.