Metallography performed on the corroded sample confirmed intergranular corrosion and cracking in the type 430 weld metal and in the HAZ on the tube side of the joint (Fig. 17 and 18). Corrosion proceeded preferentially at the
lower-Cr-content martensitic phase that formed preferentially along the grain boundaries. The Rockwell hardness values shown in Fig. 17 were converted from Knoop HK 500 g measurements.
Vilella’s reagent was used for etching to distinguish any martensite phase. There were no signs of fatigue cracking.