Effect of annealing temperature on microstructure and mechanical properties of 50 mm thickness 316L electron beam welded joint

The port stubs in China Fusion Engineering Test Reactor (CFETR) vacuum vessel are electron beam welded. Due to the large thickness of the plate, the residual stress after welding is large, and the microstructure of the weld from top to bottom is inhomogeneous, so it is necessary to adopt post-welding annealing to further improve the microstructure and properties. In order to explore an appropriate annealing process, a single temperature zone tubular furnace was used to anneal the electron beam welded sample of 50 mm thickness 316L stainless steel within the temperature range from 200 ℃ to 450 ℃. The grain structure of the heat affected zone and weld zone with different annealing processes was analyzed by electron backscattered diffraction (EBSD). In addition, tensile tests and microhardness tests were carried out on the top, middle and bottom areas of the joint under different annealing processes. The results show that the dislocation densities of weld zones and heat affected zones decrease with the increase of heat treatment temperature, and the third kind of internal stress caused by dislocation was released. After 300 ℃ heat treatment, the tensile strength and elongation after fracture of different areas of the joint are more excellent, and there are not too many precipitated particles in the fracture of each tensile sample. The variation trend of microhardness in each area of the joint at different annealing temperatures is approximately consistent with that of tensile strength.