Influence of welding speed on the mechanical performance and microstructural evolution of GMAW-welded SS400 steel

This study investigated the effect of welding speed on the tensile properties, hardness distribution, and microstructural evolution of robotic Gas Metal Arc Welding (GMAW)-welded SS400 steel joints. Single-pass V-groove butt joints were welded at travel speeds of 40, 50, and 60 cm/min, while welding current, arc voltage, wire-feed rate, shielding gas, and joint geometry were kept constant. Tensile testing, Vickers microhardness testing, and metallographic observation were conducted according to ASTM E8/E8M, ASTM E92, and ASTM E407, respectively. The highest mean ultimate tensile strength and yield strength were obtained at 40 cm/min, with an ultimate tensile strength of 458.50 MPa. The weld metal showed the highest hardness, with peak values of approximately 230-250 HV0.3, depending on welding speed. Changes in welding speed altered the calculated heat input and affected ferrite-pearlite morphology across the weld metal, heat-affected zone, and base metal. Although 40 cm/min produced the highest tensile response, 50 cm/min showed the most balanced combination of tensile properties, hardness uniformity, and relatively homogeneous ferrite-pearlite morphology. Therefore, 50 cm/min can be considered a suitable welding speed for achieving balanced mechanical and microstructural characteristics under the present experimental conditions.