Creep Deformation of 16Cr-8Ni-2Mo and Mod. 316 Weld Metal of 316FR Stainless Steel Welded Joints

A low carbon/ medium nitrogen 16Cr-8Ni-2Mo weld metal (16-8-2 WM) and a Mod. 316 WM were crept at 823 K-923 K to ensure long-term safety of components in fast breeder reactors (FBRs). For this purpose, creep tests were performed up to 238,064.7 hours in this study. Although the Mod. 316 WM showed longer time-to-rupture at the temperatures, the WM showed lower ductility and faster transition time to tertiary creep region relative to time-to-rupture. The behaviors were influenced by precipitation of σ phase during creep test. Matrix deformed easier because solid solution strengthening elements, i.e., Cr and Mo, diffused into the precipitate for the Mod. 316 WM with higher contents of the elements, and then WM became more brittle in association with precipitation of σ phase than the 16-8-2 WM. According to the above results, the precipitation of σ phase affects not only creep behavior but also time-to-rupture of the weld metals for 316FR steel.