Surface cracking and phase transformations associated with cathodic charging of austenitic stainless steel

Metallographic and X-ray examination have been employed to investigate the effects of cathodic charging five commercial 300 series stainless steels having different austenite stabilities. Although the introduction of hydrogen at high fugacities produces both ɛ and α martensite in all of the steels, the tendency to form ɛ is greatest in the austenite of highest stability. This is not consistent with the expected effect of stacking fault energy, but the incidence of ɛ formation is greatest in the steels with the lower Md temperatures, apparently because transformation to α martensite becomes more difficult in these circumstances. Reversion to austenite occurs to some extent on aging at room temperature and is rapidly completed when hydrogen is driven off at higher temperatures. MST/1942