Study of Factors in the Butt Welding Process of SKD11 Steel Affecting Microstructure and Mechanical Properties

Abstract

This research aims to investigate the factors in the butt welding process of SKD 11 steel that affect the microstructure and mechanical properties of the weld joint. Gas Metal Arc Welding (GMAW) was performed using a robotic welding arm with a 1.2 mm flux-cored wire electrode. The specimens had a thickness of 6 mm and were prepared with a single V-groove butt joint configuration with an included angle of 60°, a root face of 2 mm, and a root opening of 2 mm. Three experimental factors were investigated, including wire stick-out distance (10, 12, and 14 mm), wire feed rate (5, 6, and 7 m/min), and preheating temperature before welding (300, 600, and 900°C), in order to evaluate their effects on the tensile strength of the welded specimens. The obtained data were analyzed using Analysis of Variance (ANOVA). The statistical analysis revealed that, within the parameter ranges investigated in this study, no statistically significant differences were observed at the 95% confidence level. However, the experimental results and Surface Plot analysis indicated that variations in wire feed rate and preheating temperature tended to influence tensile strength and weld fusion characteristics. The maximum tensile strength obtained from the experiments was 180 MPa at a wire stick-out distance of 14 mm, a wire feed rate of 6 m/min, and a preheating temperature of 600°C. Microstructural analysis showed that the weld zone and the Heat Affected Zone (HAZ) consisted mainly of pearlite, ferrite, and carbide phases. In addition, carbide precipitation was observed in several regions, particularly at elevated preheating temperatures. These conditions promoted tempering of the metallic structure, reduced residual stress, and improved the metallurgical stability of the welded joint.