Energiewerke Nord (Germany)

Abstract Hydrogen emerged as a solution to increasing environmental problems and is becoming an important energy resource. However, hydrogen can deteriorate the mechanical performance of metallic components. This phenomenon is known as hydrogen embrittlement (HE). Engineering steels, such as nickel-chromium-molybdenum steels, are widely used in the industry and can be attractive materials for hydrogen applications such as pressure vessels, owing to a good combination of tensile strength (up to 1.1 GPa) and ductility (e.g., 10 % or higher). They can decrease product weight and reduce construction costs. However, as HE susceptibility tends to increase with increasing strength of steels, high-strength steels are susceptible to HE when used in hydrogen gas environment. The aim of this paper is to investigate the susceptibility of different engineering steels to hydrogen embrittlement. Three martensitic Cr-Ni-Mo steels were investigated. Slow strain rate tests were performed in gaseous hydrogen at 100 bar (10 MPa) and room temperature. Microstructure characterization and fractography study were carried out. Ni-Cr-Mo steels show a martensitic microstructure with precipitates in quenched and tempered condition. Their YS and UTS are higher than 1000 MPa (145 ksi) and 1100 MPa (159 ksi), respectively. Hydrogen gas degrades the ductility of Cr-Ni-Mo steels considerably, while strength deteriorates slightly. Fractography is characterized by a brittle fracture assisted by hydrogen. Hydrogen-Enhanced Localized Plasticity (HELP) is seen to be the primary failure mechanism in martensitic steels.