Microstructure and properties analysis of welded joint of 22MnB5/QStE550TM dissimilar steel
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.
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