Polarization Behavior of Welded Austenitic Stainless Steel in Boiling 42% MgCl₂ Solution

Abstract

The polarization behavior of a welded joint of SUS 304 stainless steel was investigated in boiling 42% MgCl₂ solution, and the effects of the variations of the residual stress and metallurgical factors coused by welding and machining after welding on the polarization behavior were discussed. Furthermore, the polarization behavior was studied under the applied stress of 25kgf/mm², and the relation between this behavior and the susceptibility to stress corrosion cracking was discussed.
The results obtained were as follows:
In the polarization behavior of the weld metal zone, a wide unsteady passive region existed. However, the unsteady passive region was narrow for the base metal zone and was not existent for the heat affected zone.
It was clarified that this difference in polarization behavior was due to the differences of alloyed Cr and Ni concentration, metallurgical structure and residual stress values.
In the case of unloaded situations, it was deduced that the heat affected zone was most sensitive to stress corrosion cracking, while the weld metal zone was immune to stress corrosion cracking.
In the case of loaded situations, all the polarization behaviors changed to more sensitive behaviors to stress corrosion cracking, It was to more sensitive behaviors to stress corrosion cracking. It was concluded from these behaviors that the base metal zone was most sensitive to stress corrosion cracking.