Abstract
This paper was intended to investigate the correlation between the polarization behavior and the susceptibility to stress corrosion cracking (SCC) of the welded joint of commercial SUS304 type austenitic stainless steel in 42% boiling MgCl2 solution.
As for the susceptibility to SCC of each part of the specimen welded with heat input of 30000J/cm, the base metal zone was the most susceptible and the heat affected zone was more susceptible than the deposited metal zone. This result agreed with the order of SCC susceptibility estimated from their polarization behaviors.
The polarization behavior of each part and the SCC susceptibility in the welded joint were influenced remarkably by the amount of heat input; the pitting potential in the polarization curve of the base metal zone shifted toward more noble potential with increasing heat input, while that of the heat affected zone behaved vice versa.
In the potentiostatic SCC test of the welded joint of which all parts were immersed in the test solution, the most susceptible part shifted from the base metal zone to the heat affected zone with increasing weld heat input. This phenomenon agreed also with SCC susceptibility estimated from their polarization behaviors.
As for the crack morphology of the base metal zone and the heat affected zone, transgranular cracking occurred with anodic polarization, while intergranular cracking appeared also with cathodic polarization. The crack morphology of the deposited metal zone had a characteristic dendritic structure in which transgranular and intergranular cracking were mixed. These results mean probably that the corrosion potential of the specimen was an important determining factor of crack morphology.
