Effect of welding process on the microstructure and mechanical properties of Fe-Cr-Ni-Mo deposited metals

In this research, 785 MPa grade Fe-Cr-Ni-Mo deposited metals were prepared by tungsten inert gas (TIG) welding and metal active gas arc (MAG) welding processes, respectively. Scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction were adopted to characterize the microstructure and crystallographic characteristics of the deposited metals. The results showed that the microstructure prepared by different welding processes composed of lath bainite. However, a large amount of coalesced bainite appeared in the microstructure of the TIG deposited metal (DM-TIG). In addition, there were a large number of inclusions in the MAG deposited metal (DM-MAG) due to the active shielding gas. After electron backscatter diffraction analysis, results indicated that the crystallographic orientation of DM-MAG was complex compared to DM-TIG due to the large number of autocatalytic nucleation. The results of the mechanical properties of different deposited metals indicted that the toughness of DM-TIG was significantly better than that of DM-MAG. This was due to the large-sized inclusions in DM-MAG, which became the source of cracks during the fracture process. In practical engineering application, welding method should be selected reasonably for components with high requirement of low temperature toughness.