Martensite Fractions Measured by XRD on Fracture Surfaces of Austenitic Stainless Steels Tensile Tested in Gaseous Helium and Hydrogen

Although martensitic transformation is neither necessary nor sufficient to explain hydrogen effects in austenitic stainless steels, the formation of a second phase upon straining results in local strain incompatibilities within the microstructure which can result in hydrogen assisted crack initiation. The fraction of α’-martensite on fracture surfaces of ten commercial austenitic stainless steels of different austenite stability was measured by quantitative x-ray diffraction (XRD). The main results are: (1) for a given steel, martensite contents on fracture surfaces of specimens tested in helium were higher compared to those tested in hydrogen and (2) tensile reduction in area of the specimens tested in hydrogen decreases with increasing martensite content on the fracture surface.