Effect of welding methods on microstructure and mechanical properties of 1 000 MPa grade deposited metal

With the same heat input, deposited metals were welded with 1 000 MPa grade solid welding wire as filler material by MAG (Metal Active Gas) and TIG welding methods, respectively. The effects of welding methods on microstructure and properties of deposited metals were studied by means of optical microscopy, transmission electron microscope (TEM) and fracture analysis etc. The results show that the deposition efficiency of MAG is significantly higher than TIG, and there is a clear "finger penetration" in MAG weld bead. The microstructure of primary weld region and reheated weld region of MAG deposited metal is significantly coarsing than TIG. TIG diposited metal has more refinement microstructure. The distribution is diversification and it includes more uniform distribution of retained austenite, which is one of the reasons for excellent low-temperature impact toughness. Besides, a large number of non-metallic inclusions in the MAG diposited metal, which is the initiation source of cleavage fracture. Therefore, non-metallic inclusion is another reason for deterioration low temperature impact toughness of MAG diposited metal. The results show that the integrated mechanical property of TIG diposited metal is much better than MAG, which is generated by the welding method for different microstructure type, morphology and characteristic of the non-metal inclusion.