Abstract
Intergranular stress corrosion cracking (IGSCC) in heat affected zone (HAZ) for supermartensitic stainless steel was studied. Two grades of the steel, lean and high grades, were heat-treated for simulating welding thermal cycles. Cracks were observed in some simulated HAZ specimens by all four methods of SCC test, U-bend, four point bent (4PB), slow strain rate technique (SSRT) and single edge notch bend (SENB) methods. It suggests that even smoothly machined specimen can detect IGSCC as long as the specimen is sensitized sufficiently and immersed in severe corrosion environment. Thermal cycle conditions inducing the cracking were clarified by U-bend SCC test for the lean and high grade steels. The results revealed that the high grade steel has higher resistance to IGSCC than the lean grade steel, and that post welding heat treatment (PWHT) is effective to prevent IGSCC. Chromium depleted zones were confirmed on prior austenite grain boundary adjacent to carbides that precipitated on the grain boundary for the lean grade steel. In these results, it was concluded that IGSCC in HAZ for supermartensitic stainless steel is caused by chromium depletion on prior austenite grain boundary accompanied by re-precipitation of chromium carbide during girth welding.
