Hydrogen-Induced Transformation and Embrittlement in 18-8 Stainless Steel

Abstract

The relation between hydrogen-induced transformed phases and embrittlement was examined in 18-8 stainless steel. The results obtained are as follows:(1) The maximum of embrittlement is observed at −15°C in 18-8 stainless steel (fcc) when the steel is charged with hydrogen at cathodic current density ic=0.2 A/cm2 for 1 hr. This behavior of embrittlement is similar to that in bcc metals.(2) At the early stage of hydrogen absorption transformed phases, “εH” and “γH”, are found which seem to be hydrogen-absorped unstable phases of ε and γ respectively. These phases changes by the discharge of hydrogen as follows:(This article is not displayable. Please see full text pdf.) (3) As for the relation between cracking and phase transformation, it is shown that cracks occur just after the transformation of εH and γH to ε, α′ and γ.(4) Apparent activation energies Q obtained from the recovery of ductility and the transition from εH to ε+α′ are estimated 10.5 and 13.3 kcal/mol respectively. These values are nearly equal to the value of the activation energy which has been measured for the diffusion of the hydrogen through austenitic stainless steel. Then the structural change of εH phase accompanied with the discharge of hydrogen and hydrogen embrittlement seem to be connected with the diffusion of hydrogen through 18-8 stainless steel.