Effect of welding mode and filler metal on microstructure and mechanical properties of dissimilar joints of S900MC thermomechanical steel to St52 carbon steel welded by gas tungsten arc welding

In this research, S900MC thermomechanical steel was jointed to St52 carbon steel through a gas tungsten arc welding process in the continuous and pulsed modes. The welding was performed in two different weld designs of V-groove and close square, with and without using an ER70S filler metal, respectively. Furthermore, the microstructure, hardness, and tensile strength of the joints were investigated. A bainitic microstructure was observed in the weld metal of the samples jointed in the continuous mode. While the weld metal microstructure of the pulsed joints was changed from a ferritic microstructure to a tempered martensitic microstructure by implementing filler metal in the V-groove weld design. In all joints, the heat-affected zone was narrower at the S900M side and had a fine bainitic microstructure. Among all joints, the maximum hardness of 389 HV was achieved for the weld metal of V-groove joints welded in the pulsed mode. At a normal strain rate, there was no considerable contrast between the yield and tensile strength of all joints, however, the elongation of the continuous joints was better than that of the pulsed joints. Increasing the strain rate led to the drastic improvement of yield and tensile strength of the joint welded in the continuous mode without using filler metal.