Development of modified alloy 52 filler metal for weldability

Alloy 690 was developed to improve resistance to Primary Water Stress Corrosion Cracking (PWSCC) compared with conventional Alloy 600. Alloy 690 weld metal (Alloy 52 filler metal) is also used in PWR nuclear power plants for welding of dissimilar-metal joints, such as safe-end welds of reactor vessels. Alloy 52, however, tends to be inferior to Alloy 600 weld metal (Alloy 82 filler metal) in terms of weldability due to its large amount of oxide scale generation on the weld bead surfaces. In this study, the effects of alloying elements on hot-cracking susceptibility and oxide scale generation were investigated in Alloy 52 filler metals. By means of cracking tests and cladding tests, investigation results were obtained as follows; 1) Increase of Nb and S contents increase hot-cracking susceptibility, although Ta dose not influence hot-cracking susceptibility. 2) Al and Ti contents influences amount of oxide scale generation. Modified Alloy 52 filler metal, which was developed based on the investigation results, showed improvements in suppression of oxide scale generation and hot cracking susceptibility. (author)