The mechanical and fatigue properties of 18Cr–4.8Ni–0.03C stainless steel were measured under high–pressure gaseous hydrogen. Slow– strain–rate tensile
(SSRT) tests were carried out at temperatures of 228 K, 293 K, and 363 K under 105 MPa high–pressure gaseous hydrogen and 0.1 MPa nitrogen. The relative tensile
strength was 0.98 or higher at all temperatures, confirming that this steel has good hydrogen compatibility. Rotating bending fatigue tests were carried out at room temperature under 88 MPa high–pressure gaseous hydrogen and air. Fatigue limits were found in both types
of atmosphere. No deterioration of the fatigue limit was observed in the specimen tested under 88 MPa high–pressure gaseous hydrogen. Surface cracks were
observed in the parallel part of the rotating bending fatigue test specimen that was unbroken at 107 cycles in both types of atmosphere.