Ductility loss of a metastable austenitic stainless steel and its TIG weldment due to hydrogen embrittlement at low temperatures considering the effect of pre-strain at 4K

Abstract

The amount of martensite in austenitic stainless steels produced during plastic deformation at low temperatures is related to the reduction in hydrogen embrittlement resistance. A pre-strain at 4 K was employed in this work to produce strain-induced martensite (SIM) in the microstructure of SUS316L and its weldment to verify the changes in hydrogen embrittlement susceptibility through slow strain tensile (SSRT) tests in a high-pressure hydrogen environment. As the base metal specimens, the weld metal specimens, manufactured by gas tungsten arc welding (GTAW or TIG) were pre-strained at different levels (5%, 10%, and 15%) for comparison with the non-pre-strained condition. Analysis of the most degraded samples tested from -150 °C to 0 °C is conducted through fracture surface observations, lateral crack length measurement, and crack densities. It was possible to indicate that the pre-strain effect induced earlier crack nucleation in comparison to the situation observed in the non-pre-strained material. Moreover, the pre-existing martensite produced by the pre-strain at 4 K is responsible for earlier crack nucleation, leading to a loss in the hydrogen embrittlement resistance for the SSRT pre-strained base metal specimens.