Welding of S700MC steels by robotic mag welding method with flux-cored wire and investigation of mechanical properties

In this study, the weldability capabilities of S650 steel and Strenx S700MC high-strength structural steel with solid welding wires were experimentally investigated using robotic technology arc welding method. Ten different samples were used in butt welds made by the push welding method using a 1.2 mm thick welding wire and a shielding gas consisting of 82% Argon and 18% carbon dioxide. Experimental studies were completed by changing the welding speed at six different speeds between 300 mm/min and 550 mm/min, the wire speed at five different speeds between 500 mm/min and 750 mm/min, and the current value at five different values between 160 amperes and 220 amperes. The throat of the weld and the widths of the weld seam were evaluated by measuring. Micro hardness values taken from the weld seam, interfacial surface, and base material were examined. As a result of keeping the welding speed constant and increasing the wire speed and the current used, it was obtained that the weld seam width increased and the penetration was more. In addition, when the measured hardness values were examined, it was observed that the hardness values increased in both the weld seam and the interfacial region. With the further increase of wire speed and current, it was observed that a homogeneous structured weld seam was formed, there was more penetration in the root region, and with the increase in energy density in the welding region, there was an increase in hardness values in all regions of the sample. In addition, it was observed that the weld root became more oval. With the gradual increase of the welding speed at constant wire speed and current values, the microstructure formed in the weld seam region of the sample exposed to the lowest welding speed (350 mm/min) shows a fine-grained distribution. In the sample where the welding speed is the highest (550 mm/min), it is seen that a thick ferrite matrix is formed within the homogeneous structure. When the Heat Affected Zone (HAZ) was examined with Scanning Electron Microscope (SEM), it was observed that the perlite structure was thinner and more homogeneous with the presence of grain growth in the microstructure. It was observed that the hardness increased due to the formation of a fine-grained and homogeneous microstructure in the HAZ region when high wire speed and current were applied. Keywords: Hardness, robot welding, S700MC steel