Effect of Residual Elements on Fracture Characteristics and Creep Ductility of Type 308 Stainless Steel Weld Metal

Abstract

Previous studies had shown that conventional type 308 stainless steel weld metal can have low creep ductility (< 1 percent total elongation) at 650 deg C. This paper demonstrates that the low ductility results from internal cracks that develop at austenite-sigma phase boundaries and propagate under the test conditions. The sigma phase is formed from ferrite present in the as-deposited weld metal. Type 308 stainless steel weld metal containing controlled amounts of the residual elements B, P, and Ti also contains sigma phase, but phase boundary cracking has not been observed even after 5000 hr. The controlled residual element weld metal is significantly more ductile (> 10 percent total elongation) than the conventional weld metals for which data are available.