Effects of external and internal hydrogen on tensile properties of austenitic stainless steels containing additive elements

Effect of hydrogen on the slow strain rate tensile (SSRT) properties of five types of austenitic stainless steels, which contain small amounts of additive elements (e.g., nitrogen, niobium, vanadium and titanium), was studied. Some specimens were charged by exposing them to 100 MPa hydrogen gas at 543 K for 200 hours. The SSRT tests were carried out under various combinations of specimens and test atmospheres as follows: (i) non-charged specimens tested in air at room temperature (RT), (ii) non-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, (iii) hydrogen-charged specimens tested in air at RT, (iv) hydrogen-charged specimens tested in 0.1 MPa nitrogen gas at 193 K, and (v) non-charged specimens tested in 115 MPa hydrogen gas at RT. In the tests without hydrogen (i.e., cases (i) and (ii)), the reduction of area (RA) was nearly constant in all the materials, regardless of test temperature. In contrast, in the tests of internal hydrogen (cases (iii) and (iv)), RA was much smaller at 193 K than at RT in all the materials. It was revealed that the susceptibility of the materials to hydrogen embrittlement (HE) can successfully be estimated in terms of the nickel equivalent, which represents the stability of austenite phase. The result suggested that the nickel equivalent can be used for evaluating the material compatibility of austenitic stainless steels for hydrogen service.