The effect of alloying elements such as titanium or phosphorus, and the effect of PWHT on
SCC susceptibility of super martensitic stainless steel welded joints were examined. On the basis of the
sensitization mechanism due to the formation of Cr-carbides, the effect of titanium on the SCC
susceptibility was determined. It is revealed that the super martensitic stainless steel (0.01C-12Cr-6.5Ni-
2.5Mo) without titanium suffered SCC in the specific region of the TTS diagram (Time - Temperature -
Sensitization) during the 2nd thermal cycle of the simulation HAZ. On the other hand, the super
martensitic stainless steel of the Ti-alloyed type (0.01C-12Cr-6.5Ni-2.5Mo-0.1Ti) was immune to SCC
in the same thermal cycle conditions. From these results, titanium is considered to prevent the formation
of Cr-carbide, which can promote the Cr-depletion along the prior austenite grain boundary, by TiC
formation. However, even if the titanium could suppress the Cr-carbide formation, it was reported that
the Ti-alloyed high grade steel girth welds in as-welded condition showed IGSCC along the high
temperature HAZ. Therefore, in this study, the effect of phosphorus was also examined. It was revealed
that the SCC susceptibility of the welded joints in as-welded condition decreased with the lowering of
the phosphorus content in steels. The TEM observation revealed that Cr-depletion along the grain
boundary in the vicinity of the surface oxide layer on HAZ disappeared after PWHT, and molybdenum
enrichment along the grain boundary was also observed after PWHT. The Laves (?) phase which
contained phosphorus was observed on the grain boundary after long duration PWHT. The good SCC