Hydrogen Environment Embrittlement of Steels and Alloys In 70 MPa Hydrogen at Room Temperature

Hydrogen environment embrittlement (HEE) of steels and alloys to be used in high-pressure hydrogen storage for fuel cell vehicles was investigated in 70 MPa hydrogen at room temperature. Candidate materials for high-pressure hydrogen storage, namely, stainless steels (i.e., SUS304; in the Japanese Industrial Standard (JIS), SUS316, SUS316L, SUS316LN, SUS310S, SUS630(17-4PH)), a low-alloy steel (SCM440), carbon steels (SUY, S15C, S35C, S55C and S80C), an iron-based superalloy (SUH660(A286)), Ni-based superalloys (Incoloy 800H, Inconel 718, Inconel 750, Hastelloy B2, Hastelloy C22), a copper-zinc alloy (C3771) and an aluminum alloy (A6061), were tested. SWP (piano wire), and SUS304, SUS316 and SUS631(17-7PH) wires used for springs were also tested. Tensile tests were conducted at room temperature using specially designed apparatus developed by our laboratory to measure the actual load on a specimen with an external load cell irrespective of the axial load caused by the high pressure and friction at sliding seals. In materials that contain Ni, i.e., stainless steels, and iron-based and Ni-based superalloys, HEE shows a variable Ni content dependence. We found that the effect of Ni equivalent on HEE of these materials shows a stronger dependence. HEE decreases with increasing Ni equivalent with grain boundary fracture or transgranular fracture along a martensite lath assisted by hydrogen for SUS630, SUS304, SUS316, SUS316LN and SUS316L. No HEE is observed in the given Ni equivalent range with dimple fracture for SUH660, SUS310S and Incoloy 800H; however, HEE increases with increasing Ni equivalent with transgranular fracture along a slip plane, that is along the interface between austenite and gamma', and with grain boundary fracture assisted by hydrogen for Inconel 718, Inconel 750, Hastelloy C22 and Hastelloy B2. These results and other HEE test results in high-pressure hydrogen obtained by AIST, i.e., results for 18 Ni maraging steel, low-alloy steels, high-Cr steels, Ni-based superalloys; are summarized in the AIST HEE data, which is compatible with NASA HEE data. HEE of the materials in high-pressure hydrogen is discussed. Internal reversible hydrogen embrittlement (IRHE) of some thermally hydrogen-charged austenitic stainless steels is also discussed in comparison with HEE of the steels.