Influence of Hydrogen on the Tensile and Fatigue Properties of the Martensitic Stainless Steels 17-4 PH and S165M

Components, such as valves and piping, which are exposed to high pressure hydrogen gas are often manufactured from high nickel, annealed 316 and 316L in order to mitigate hydrogen embrittlement. Martensitic stainless steels present an alternative to austenitic stainless steels for certain components; however, many questions remain about the suitability of these steels for hydrogen applications. In this study the influence of hydrogen on the mechanical behavior of martensitic stainless steels, 17-4 PH P1070 (H1025), 17-4 PH P930 (H1150), and S165M, was investigated through tensile and fatigue testing performed in situ in hydrogen gas. Tensile testing was performed with smooth specimens at hydrogen gas pressures up to 875 bar at room temperature. Load-controlled fatigue testing was performed at room temperature and at a hydrogen gas pressure of 100 bar with circumferentially-notched tensile specimens with an elastic stress concentration factor of 2. The reduction of area and total elongation of 17-4 PH P1070 and S165M was decreased at hydrogen gas pressures greater than 3 bar. At all tested pressures the reduction of area and total elongation of 17-4 PH P1070 was reduced more than for S165M, which corresponds to the higher strength of the 17-4 PH P1070. S165M and 17-4 PH P1070 exhibited similar fatigue life at higher stress amplitudes; however, 17-4 PH P1070 exhibited slightly longer fatigue life at lower stress amplitudes. A large amount of scatter was observed in the cycles to failure of 17-4 PH P930 tested in hydrogen, and an instance of lower cycles to failure was attributed to crack initiation at a surface defect. Both 17-4 PH P1070 and S165M exhibited longer fatigue life than austenitic stainless steel 316L tested with the same conditions, indicating the viability of these steels for components in hydrogen applications with relatively mild stress concentrations and primarily elastic stresses.