Effect of hydrogen on dislocation structure and strain-induced martensite transformation in 316L stainless steel

Hydrogen embrittlement behavior with respect to strain-induced martensite (SIM, alpha') and the dislocation structure in 316L stainless steel were investigated using tensile testing at strain rates of 2 x 10(-6) to 2 x 10(-2) s(-1) at room temperature. The deformed specimens with and without hydrogen were examined using MFM, neutron diffraction, TEM, and a Feritscope. The results showed that ductility, tensile stress, and hardness increased with decreasing strain rate and an increasing amount of SIM. Hydrogen caused SIM to be distributed locally in a alpha'/gamma laminated structure. The H-free sample had a larger quantity of SIM than the H-charged sample at the same plastic strain. Hydrogen changed the dislocation structure from only cellular to a mixed structure comprising both cellular and planar dislocations. H-charged 316L SS had a diffuse reflection, which implied that short-range ordering formed during tensile testing. It was concluded that hydrogen induced planar dislocation and suppressed SIM formation, leading to cleavage fracture and softening.