Straining-temperature dependence of vacancy behavior in hydrogen-charged austenitic stainless steel 316L

The vacancy behavior in austenitic stainless steel 316L with high γ-phase stability in a hydrogen environment was investigated to clarify the critical defects of hydrogen embrittlement. Hydrogen was introduced in the samples by the high-pressure gas method and tensile straining was conducted at variable low temperatures. Characterization of the strain distribution and vacancy defects was performed by SEM-KAM and low-temperature positron annihilation lifetime spectroscopy measurements, respectively. Upon straining at low temperatures (<-70 °C), high-strain regions were induced locally where a high concentration of vacancies accumulated. These vacancies agglomerated into large clusters that are thought to develop into the embryos of larger voids leading to cracks. These results show that the local formation of hydrogen-induced vacancies in high-strain regions is the determining factor of hydrogen embrittlement in austenitic stainless steel 316L.