Improvement of Mechanical Properties of G115 Steel Welded Joint by Adjusting Welding Current

G115 martensitic heat-resistant steel has been widely used in high parameter thermal power units because of its excellent mechanical properties and oxidation resistance. The microstructure and mechanical properties of single pass G115 steel welded joints fabricated by different welding currents were investigated in this study. The results show that larger welding current causes the widening of martensite laths, the coarsening of M23C6 carbides and the decrease in Vickers hardness in weld metal. However, welding current will affect evidently the microstructure and Vickers hardness of heat-affected zones only when it reaches to 120 A, which is mainly manifested by larger diameter and lower area fraction of M23C6 carbides and lower Vickers hardness. The tensile strength of welded joint firstly decreases and then increases with the increase in welding current, while the yield strength and elongation firstly increase and then decrease. The welded joint with welding current of 100 A is more recommended, due to the combination of highest yield strength and best ductility.