Interpretation of the Behavior of Carbide Precipitation in Heat Affected Zone of Supermartensitic Stainless Steel Using Strain Aging Phenomena

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.