1991 Volume 40 Issue 4 Pages 235-238
The influence of Mo content variation approved in the standard in Type 316 stainless steel was investigated electrochemically to the localized corrosion characteristics in chloride solution. The shift in pitting potential Vc′ 10, which corresponds to film breakdown, was changed a little by decreasing content of Mo in the regulated range, but magnificently in Vc′ 100, corresponding to a primary dissolution stage of the pitting. Anodic polarization characteristics of active pit anode, measured by using an artificial pit, were affected remarkably by the difference of content of Mo in 2% to 3%. Dissolution current of the active pit anode at a same potential increased in the magnitude of about 5 times in 2% Mo larger than in 3% Mo. These facts suggest that the Mo content variation approved in the standard do not affect to initiation stage of pitting so much, but strongly to propagation of pitting, which is similar to dissolution process of crevice corrosion and SCC. Recent 316, of which Mo content is controlled strictly at a lower limit in the standard, has a poor resistivity against the localized corrosions in chloride media.
