Characterization of Intergranular Corrosion in Heat-Affected Zone of Low Carbon 12Cr-Ni Ferritic Stainless Steel

Abstract

Intergranular corrosion in heat-affected zone of low carbon 12Cr-Ni ferritic stainless steel was investigated by the method of practice Z in ASTM A 763-93. The microstructure of welded joint was characterized using an optical microscope and a scanning electronic microscope. Severe intergranular corrosion (IGC) was only observed in low temperature heat-affected zone (LTHAZ) adjacent to base metals at the back of the welded joints in unstabilized steel. On the other hand, IGC was not observed in the welded joints of stabilized steels. According to the analysis of microstructure, the severe IGC is attributed to both the precipitated phase along the grain boundaries inducing the presence of chromium-depleted zone and the welding residual tensile stress promoting the corrosion. Therefore, stabilized elements addition such as Ti and Nb is required in order to avoid the IGC in welded joint of these steels. Relief residual tensile stress by post weld heat treatment would also be an effective method to avoid the IGC in the welded joints of these steels.