Effect of preheating temperature on the mechanical properties and microstructural evolution of smawwelded ASTM A36 steel

This study examines the effect of preheating temperature (N/A, 150 °C, 250 °C, and 350 °C) on the mechanical performance and microstructural evolution of SMAW-welded ASTM A36 steel. Welding was performed under controlled conditions using E7016 and E7018 electrodes, and joint properties were evaluated through tensile testing, Vickers hardness profiling, and metallographic analysis in the WM, HAZ, and BM regions. The ultimate tensile strength remained relatively stable (443–446 MPa), whereas yield strength and ductility varied with preheating temperature. The 250 °C condition yielded the highest yield strength (315.68 MPa) and the most uniform hardness distribution, indicating moderated cooling behaviour. Microstructural analysis revealed a refinement–stabilisation– coarsening trend with increasing preheat, with 250 °C producing the most homogeneous ferrite–pearlite structure, while 350 °C promoted grain coarsening and softening.