Effect of pre-strain on hydrogen induced cracking of PAW welded 304 austenitic stainless steel

Abstract

Strain-hardened austenitic stainless steel (γ-SS) is extensively used in high-pressure hydrogen systems after welding. The weld may experience varying degrees of hydrogen embrittlement (HE) with different levels of pre-strain, which seriously threatens the reliability of hydrogen systems. Therefore, it is vital to research the effect of pre-strain on hydrogen-induced cracking of γ-SS welds. In this research, the impact of hydrogen on the mechanical properties of type 304 γ-SS plasma arc welding (PAW) welds with different levels of pre-strain are studied through slow strain rate tensile (SSRT) test. The pre-strain of the weld after hydrogen charging is optimized, then the causes of hydrogen-induced cracking are illustrated by microstructure analysis. The weld metal zone (WMZ) has a greater HE susceptibility than the base metal zone (BMZ). The HE susceptibility of the weld can decrease after solution-treated. The fracture of the weld with pre-strain of 5% is mainly due to dislocation and ferrite increasing the HE susceptibility. When the pre-strain is above 10%, the weld metal and the base metal have undergone a severe transformation from austenite to α′ martensite. The content of α′ martensite rises with the rising pre-strain. The HE susceptibility of the weld is greater than the base metal due to the influence of dislocations and ferrite. The brittle fracture is initiated primarily at the phase boundary. The strength of welds can be improved while keeping good HE resistance with pre-strain of 5%.