Evaluation of the Effect of Heat Input on Welded Joint Properties of ASTM A572 Grade 50 Steel Using the GMAW Process with 90Ar-10CO2 Shielding Gas and Spray Metal Transfer

In this study, the influence of heat input on the mechanical properties and microstructure of welded joints in ASTM A572 grade 50 steel using the GMAW process and 90Ar-10CO2 shielding gas was investigated. Process parameters were varied between 20-30 V and 230-250 A, which were adjusted aiming to obtain spray transfer together producing two heat inputs with a 10% difference between them. Visual inspection, tensile tests, microhardness scans, measurements of the width of the heat-affected zone (HAZ), and metallography were performed. The experimental measurements were complemented by calculating the continuous cooling transformation (CCT) diagram of the steel from its chemical composition. The results showed that discontinuity-free and visually acceptable welded joints were obtained. The microstructure of the fusion zone was primarily composed of acicular ferrite, and the HAZ contained a mixture of bainite, pearlite, and ferrite as calculated by the CCT diagram. No statistically significant variations were observed in the microhardness measurements, with the highest value (240 MHV) obtained in the fusion zone. The width of the HAZ varied proportionally with the heat input, while no significant differences were found in the stress results as a function of the heat input.