Effect of Preheating Temperature and Joint Geometry on HAZ Development and Hardness of GMAW-Welded SAE 1045 Steel, and on the Mechanical Performance of Butt Joints

Medium-carbon steels are susceptible to heat-affected zone (HAZ) hardening during welding. This study evaluated the effects of preheating temperature and joint geometry on mechanized gas metal arc welded (GMAW) joints in 6.3 mm thick SAE 1045 steel. Butt and fillet joints were welded under conventional single-pass conditions from room temperature to 250 ◦C, while an additional two-pass procedure was evaluated separately. Metallography and hardness were evaluated for both joint geometries, whereas tensile and Charpy V-notch tests were performed only on butt joints. Significant joint geometry × preheating condition interactions were identified for weld metal (WM) area, HAZ area, WM hardness and HAZ hardness. Average HAZ hardness remained below 300 HV10 for all conventional single-pass conditions. Among the butt joint single-pass conditions, no statistically significant effect of preheating was detected for ultimate tensile strength (UTS) or Charpy absorbed energy, and all tensile specimens fractured in the base metal (BM). The two-pass procedure was treated descriptively because the second deposition simultaneously altered multiple welding variables. Overall, the effects of preheating on WM and HAZ areas and hardness were joint-geometry-dependent under the investigated conditions.