退火温度对50 mm厚316L电子束焊接头微观组织与力学性能的影响

中国聚变工程实验堆(China Fusion Engineering Test Reactor，CFETR)真空室窗口领圈的组焊采用电子束焊，由于板厚较大，焊后残余应力较大，且焊缝从顶部到底部存在组织不均匀性，需要采用焊后退火处理进一步优化组织性能. 为了探索合适的退火工艺，采用单温区管式炉对50 mm 316L不锈钢电子束焊试样在200 ~ 450 ℃的范围内进行了退火试验，并采用电子背散射衍射(electron backscattered diffraction，EBSD)手段分析了不同退火工艺下接头热影响区及焊缝的晶粒组织. 对不同退火工艺下接头的顶部、中部与底部区域进行了拉伸试验和显微硬度测试. 结果表明，随热处理温度的提高，焊缝及热影响区的位错密度出现下降，由此引起的第3类内应力得到释放；300 ℃热处理后接头不同区域的抗拉强度和断后伸长率都较为优异，且拉伸试样的断口中均未发现大量析出相颗粒; 接头各区域显微硬度在不同退火温度下的变化趋势与抗拉强度的变化趋势近似一致.

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.