Hydrogen embrittlement behaviors of A286 in high-pressure gaseous hydrogen and pre-charged hydrogen A286

At present, slow strain rate tensile (SSRT) test is widely used as a method for evaluating the hydrogen compatibility of metallic materials. There are two types of SSRT: one is conducted in high pressure gaseous hydrogen, and the other is executed using pre-charged hydrogen specimen. The former requires high pressure gaseous hydrogen equipment to maintain the pressure during the test. The latter requires the appropriate hydrogen pressure and temperature for the pre-charge to be adjusted so that the hydrogen content has a uniform cross-sectional distribution. In this study, we used electron backscatter diffraction and other methods to investigate the differences in the hydrogen embrittlement mechanisms of high strength iron-based superalloy A286 with austenitic phase in 70 MPa gaseous hydrogen and 56 ppm hydrogen charged A286. As a result, for the specimen in high pressure gaseous hydrogen, localization of strain was observed in the outer layer near the fracture surface. In addition, surface cracks were observed on the side surface near the fracture surface. Therefore, it is thought that hydrogen embrittlement due to the hydrogen enhanced plasticity or hydrogen enhanced strain-induced vacancies mechanisms is dominant. On the other hand, for the hydrogen-charged A286, a decrease in the Kernel average misorientation value in the center of the specimen was observed, and no cracks were observed on the side surface. This is thought to be the result of hydrogen directly reducing the bonding strength due to the hydrogen enhanced decohesion mechanism. From those results, it can be clarified that the hydrogen embrittlement mechanisms for A286 differ depending on the hydrogen environments.