Abstract

The mechanisms of hydrogen embrittlement in AISI type 316 austenitic stainless steel have been investigated by in situ straining in a high-voltage electron microscope (HVEM) equipped with an environmental cell. Hydrogen effects on strain-induced phase transformations, the generation rate and velocity of dislocation, and crack propagation rates were studied. The salient features of the fracture were similar for cracks propagating in vacuum and in hydrogen gas. In each case, ε and α′ martensite formed at the crack; the ε phase extended ahead of the crack while the α′ phase was restricted to high stress regions near the crack tip. The principal effect of hydrogen was to decrease the stress required for dislocation motion, for phase transformation of the austenite, and for crack propagation.

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