Abstract: In the experiment, different thickness of 22MnB5 steel with 1.8 mm thickness and QStE550TM steel with 2 mm thickness are welded by TIG welding. The microstructure of the characteristic area of the welded joint of different steel is observed by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The mechanical properties of dissimilar steel welded joints are analyzed by universal mechanical testing machine and Vickers hardness tester. The experimental results show that the microstructure of the heat affected zone on the QStE550TM side is granular bainite, the microstructure of the weld area and the heat affected zone on the 22MnB5 side is lath bainite, and part of the oxide inclusion in the heat affected zone on the 22MnB5 side induces the formation of acicular ferrite. The average grain size in the weld area is 4 μm, and the proportion of grain boundaries with large angle in the weld area is about 53%. The second phase Ni-Cr-Fe solid solution was found in the characteristic region of the dissimilar steel welded joint. The average tensile strength of the two groups of tensile samples is 660.5 MPa. The highest hardness area of the welded joint is 22MnB5 base metal, and the lowest hardness area is QStE550TM side heat affected zone. There is carbon migration in the heterogeneous steel joint. A carburized layer of about 43 μm appears near the fusion interface of 22MnB5 side, and a decarburized layer of about 35 μm appears in the heat affected zone of QStE550TM side. However, combined with the analysis of the mechanical properties of the dissimilar steel welded joint, the carbon migration phenomenon of the welded joint has no obvious effect on the mechanical properties.

Key words: TIG welding, Microstructure, Inclusion, Mechanical properties, Carbon migration

摘要： 实验采用TIG焊对1.8 mm厚的22MnB5钢与2 mm厚的QStE550TM钢进行不等厚连接，结合光学显微镜(OM)、扫描电镜(SEM)及电子背散射衍射(EBSD)等方法对焊接接头的特征区域进行微观组织观察，使用万能试验机和维氏硬度仪分析焊接接头的力学性能。结果表明，QStE550TM侧热影响区为粒状贝氏体，焊缝区域与22MnB5侧热影响区显微组织为板条贝氏体，其中22MnB5侧热影响区的部分氧化物夹杂诱导形成了针状铁素体；焊缝区域内平均晶粒尺寸为4 μm，大角度晶界占比约为53%；在接头特征区域发现第二相Ni-Cr-Fe；两组拉伸试样的平均抗拉强度为660.5 MPa；焊接接头硬度最高的区域为22MnB5母材，硬度最低的区域为QStE550TM侧热影响区；该异种钢接头存在碳迁移现象，在22MnB5侧熔合线附近出现约43 μm的增碳层，在QStE550TM侧热影响区出现约35 μm的脱碳层。结合力学性能分析，该焊接接头的碳迁移现象未对力学性能产生明显影响。

关键词: TIG焊, 显微组织, 夹杂物, 力学性能, 碳迁移