Influence of Strain Rate on Fracture Characteristics and Diffusible Hydrogen of High Tensile Steel under Hydrogen Charging

Abstract

Hydrogen embrittlement susceptibility is known to vary with decreasing strain rate. In this study, influence of strain rate on ductility, fracture characteristics and diffusible hydrogen in high tensile steel sheet under hydrogen charging was investigated using the tensile test by changing strain rate, fractography and thermal desorption spectroscopy （TDS）. The ductility was lowered as strain rate decreased. Conversely, hydrogen embrittlement was not observed for the high strain rate with the magnitude in the order of 10^－3/s. The specimen with lowered ductility presented quasi-cleavage fracture and intergranular fracture. In this specimen, the faster the strain rate was, the wider and shallower the brittle fracture was distributed surrounding the test piece. On the other hand, the brittle fracture spreading to the inside was locally observed as the strain rate became slower. TDS revealed that the variation of ductility with change in strain rate depends on the hydrogen trapping sites and the amount of hydrogen trapped in dislocations and grain boundaries.