Hydrogen Embrittlement of Metals in 70 MPa Hydrogen at Room Temperature

Hydrogen embrittlement (HE) of metals used in the system of fuel-cell vehicles, i.e., high-pressure hydrogen storage tanks and vessels, compressors, valves and pipes, is investigated in 70 MPa hydrogen at room temperature. The materials tested are austenitic stainless steels (i.e., SUS304; in the Japanese Industrial Standard (JIS), SUS316, SUS316L, and SUS316LN), a low-alloy steel (i.e., SCM440), carbon steels (i.e., SUY, S15C, S35C, S55C and S80C), a Ni-based superalloy (i.e., Inconel 718), and an aluminum alloy (i.e., A6061). Tensile tests were conducted at room temperature using a specially designed equipment developed by our laboratory, which was designed to measure the actual load on the specimen with an external load cell irrespective of the axial load caused by the high pressure and friction at sliding seals. SUS304 and SUS316 showed severe HE, while SUS316L and SUS316LN showed slight HE. Fracture occurred on strain-induced martensite of the austenitic stainless steels in hydrogen. SCM440 showed extreme HE depending on heat-treatment; in particular, quenched materials showed marked HE. The carbon steels showed extreme and severe HE depending on carbon content. Inconel 718 also showed severe HE, while A6061 showed negligible HE. These results and other HE testing results which AIST has done previously are summarized in the AIST HE data table. HE behavior of the material in high-pressure hydrogen is discussed in this paper.