A Study on the Effects of Alloying Elements(Cr, Mo, W, Ni) on the Repassivation Rate and Stress Corrosion Cracking of Stainless Steels

Effects of alloying elements(Cr, Mo, W, Ni) on the repassivation kinetics of Fe-Cr stainless steels in deaerated MgCl2 solution at 50 .deg. C were examined using the rapid scratching electrode technique under a potentiostatic condition. The repassivation kinetics of the alloys was analyzed in terms of the current density flowing from the scratch, i(t), as a function of the charge density that has flowed from the scratch, q(t). Repassivation on the scratched surface of the alloys occurred in two kinetically different processes : passive film initially grew according to the place exchange model in which i(t) is linearly proportional to q(t), and then according to the high field ion conduction model in which i(t) is linearly proportional to the 1/q(t) with the slope of cBV, where c is a constant for the alloy, B is a constant related with the activation energy barrier for ion movement and V is the potential difference across the passive film. The value of cBV for an alloy was to be found to be a parameter representing the repassivation rate and the protectiveness of the passive film. The influences of alloying elements(Cr, Mo, W, Ni) on the repassivation kinetics of Fe-Cr stainless steels were quantitatively evaluated by examining the effects of these elements on the cBV, and discussed the protectiveness of passive film and the stress corrosion susceptibility of alloys in terms of the value of cBV