Abstract
In this report, the effect of microstructural change during aging at around 1000 K on the susceptibility of reheat cracking in the FCAW weld metal of Type 308 stainless steel was investigated. Precipitates in the weld metal sampled from actual equipment, which was damaged during operation, were identified and the change in the microstructures were observed with aged weld metals which were made from the flux cored wires with various Bi contents.
Ferrite contents were depressed compared with the as-welded condition and it was observed that most of the ferrite phases were transformed to σ phases and carbides in the weld metal sampled from the actual equipment. As for the aged specimen, σ phases and carbides precipitation were observed under specific aging conditions, however, Bi had no effect on incubation time for precipitation of the σ phase. Therefore, Bi does not promote the precipitation of the brittle phase. On the other hand, oxygen contents of the weld metal and hardness of the austenite phases increased with increasing Bi contents in the weld metal. This phenomenon is considered to be the dispersion hardening by oxide particles including Bi oxide and can be the secondary factor that increases the susceptibility of the reheat cracking in the FCAW weld metal.
