Association of Microstructures and Pitting Corrosion in Weld Metals of Austenitic Stainless Steels

Abstract

Measuring corrosion potential at the micro-part of the weld metal surface of many kinds of austenitic stainless steels has revealed that the ripple lines formed on the weld metal surface are apt to be anodic and be corroded by pitting. In this study, the reason why the pitting corrosion is likely to occur at the ripple lines and the phenomonon of pit-growing in a weld metal interior were discussed metallographically.
The following results were obtained: The ripple lines on the weld metal surface correspond to the bandlike regions where delta ferrite phases exist high densely. The delta ferrite phase at the ripple line supplies a site for the pitting corrosion to start, and promotes the pit progression. The mechanism for solute segregation to occur at the ripple lines was explained qualitatively from solidification metallurgy.