核电用T22-800H异种管材TIG焊接头界面组织演变及力学性能研究

Study on Microstructure Evolution and Mechanical Properties of TIG Welded Dissimilar Joints of T22-800H Tubes for Nuclear Power

对800H-T22异种和800H-800H同种管接头采用TIG熔化环的方式进行焊接。采用OM、SEM、EDS、XRD对接头的组织、相以及元素组成进行了表征分析,并对两种接头的显微硬度分布以及高温拉伸性能进行了测试。研究结果表明,同种接头和异种接头在650℃高温下抗拉强度分别达到357.1 MPa和185.9 MPa,断后伸长率分别为24.4%和14.5%。与800H同种焊接接头相比,T22-800H焊接接头在650℃高温力学性能较差。800H-800H焊接接头热影响区有析出相Ti N,焊缝区有析出相(Ti,Nb)(C,N),它的存在可提升接头高温力学性能。由XRD分析可知,在异种接头中存在体心立方和面心立方两种结构,同种接头只存在奥氏体相。异种材料焊接接头800H侧HAZ显微硬度为146.3 HV,T22侧HAZ平均显微硬度为340.7 HV,焊缝平均硬度为145.2 HV。

TIG molten ring welding was used for 800H-T22 and 800H-800H materials. The OM, SEM, EDS and XRD analysis were applied to characterize and analyze the microstructures, phase and element composition of the joints. The microhardness and high temperature tensile property were tested. The results show that the tensile strength of the same material joint and the dissimilar metal joint reaches 357.1 MPa and 185.9 MPa at 650℃, the elongation after fracture is 24.4%and 14.5%, respectively. Compared with the same material welding joint of 800H, the T22-800H dissimilar welded joint has poor mechanical property at high temperature. There are precipitated Ti N in the heat-affected zone and(Ti, Nb)(C, N) in the weld seam of 800H-800H welded joint, and their existence can enhance the mechanical properties of the joint at high temperature. XRD analysis shows that there are two kinds of phases in the dissimilar joint, which are BCC and FCC, and there is only austenite phase in the 800H-800H joint. The microhardness of the HAZ at 800H side and T22 side is 146.3 HV and 340.7 HV, respectively, and the average microhardness of weld seam is 145.2 HV.