A number of research works have been conducted for clarification of the mechanism of
intergranular stress corrosion cracking (IGSCC) in girth welds of high grade supermartensitic stainless
steel (SMSS). Although some evidence indicates that the IGSCC is caused by chromium depletion
due to carbide precipitation, more confident evidence is required for clear understanding of the
mechanism. In this context, behavior of the carbide precipitation was investigated using strain aging
phenomena. Higher aging index was observed in solution treated steel with higher carbon content.
However, no increase in aging index was observed in the sensitization treated steel with increase in
carbon content. These results suggest that carbide precipitation occurs during the sensitization
treatment. That is, it supports that the mechanism of IGSCC in high grade SMSS would be chromium
depletion accompanied by chromium carbide precipitation during girth welding.
Keywords: supermartensitic stainless steel (SMSS), intergranular stress corrosion cracking (IGSCC),
sensitization, stress corrosion cracking (SCC), linepipe, girth welding, heat affected zone (HAZ),
carbide, chromium depletion, strain aging, aging index