Minimizing distortion in flux cored arc welding of A36 steel by preheating and its effect on weld mechanical properties

Welding technology is one of the joining processes that is widely used in ship industry, but it faces some challenges such as distortion and residual stress due to local heating. Welding distortions can affect the precision and appearance of ship structures. This study aims to reduce welding distortion through preheating and its influence on weld mechanical properties, including strength and hardness are evaluated. Welding processes were conducted on ASTM A36 steel plates using flux cored arc welding (FCAW) and E71T-11 filler metal. Welding parameters used including welding current, arc voltage and speed were 110 A, 20 Volt and 1.5 mm/s respectively. Preheating treatments were applied by heating both sides of the weld using electric heater bands at various temperatures of 100, 200, and 250 ℃, and temperatures during welding were recorded with K-type thermocouples attached to the data acquisition. Several experiments including distortion, microstructure observation, hardness, and tensile testing were conducted. The results showed that increasing preheat temperature reduced welding distortion, with the best distortion reduction occurred at 250 ℃. Preheating also caused microstructural changes in the weld metal region and heat affected zone (HAZ) with the amount of ferrite being increased with increasing preheating temperature. As a result, the ultimate tensile strength (UTS) of conventional weld metal, typically 642.94 MPa reduced to 547.64 MPa after preheating at temperature of 250 ℃ but this strength reduction is compensated by its improved ductility. The mechanisms of welding distortion and strengthening under preheating treatments are discussed in this paper.