Effect of High-Pressure Hydrogen Gas on Fracture of Austenitic Steels

Applications requiring the containment and transport of hydrogen gas at pressures greater than 70 MPa are anticipated in the evolving hydrogen economy infrastructure. Since hydrogen is known to alter the mechanical properties of materials, data are needed to guide the selection of materials for structural components. The objective of this study is to characterize hydrogen-assisted fracture in two austenitic steels, 21Cr-6Ni-9Mn (21-6-9) and 22Cr-13Ni-5Mn (22-13-5), as well as explore the role of yield strength and small concentrations of ferrite on hydrogen-assisted fracture. The testing methodology involves exposure of uniaxial tensile specimens to high-pressure hydrogen gas in order to precharge the specimens with hydrogen, then subsequently testing the specimens to measure strength and ductility. In all cases, the alloys remained ductile despite precharging to hydrogen concentrations >1 at%, this is substantiated by reduction in area of >50% and fracture surfaces dominated by microvoid coalescence. Low concentrations of ferrite and moderate changes in yield strength did not affect the hydrogen-assisted fracture of 21-6-9 and 22-13-5 respectively.