Mechanical properties of a new nitrogen-strengthened stainless steel with reduced amount of Ni and Mo in high pressure gaseous hydrogen

To confirm a compatibility of a newly developed high strength stainless steel "NSSC,STH (R) 2" for hydrogen related applications, tensile and fatigue crack growth properties were evaluated in high pressure hydrogen gas up to 90MPa. At temperatures between -40 and 85 degrees C, no conspicuous deterioration of tensile properties including ductility was observed even in 90 MPa hydrogen gas at -40 degrees C while strength of STH (R) 2 was higher than SUS316L. Although a slight drop of reduction of area was recognized in one specimen tested in 90 MPa hydrogen gas at -40 degrees C, caused by the segregation of Mn, Ni and Cu in the laboratory manufactured 15mm-thick plate, it was considerably improved in the large mill products having less segregation. Fatigue crack growth rates of STH (R) 2 in high pressure hydrogen gas were almost the same as that of SUS316L in air. Although fatigue crack growth rate in air was considerably decelerated and lower than that in hydrogen gas at lower Delta K region, this was probably caused by crack closure brought by oxide debris formed on the fracture surfaces near the crack tip by the strong contact of the fracture surfaces after the fatigue crack was propagated. By taking the obtained results into account, it is concluded that NSSC STH (R) 2 has excellent properties in high pressure hydrogen gas in addition to high strength compared with standard JIS SUS316L.