The Effect of Welding Current on the Microstructure and Fatigue Failure of Q690D High-Strength Steel

This study investigates the effects of welding current on the microstructure and fatigue performance of welded joints. The findings indicate that the base material has smaller grain sizes, primarily composed of elongated rolled grains. As the welding current increases, the proportion of high-angle grain boundaries in the weld zone increases, and the grain size grows. The degree of recrystallization within the welded joint increases with the welding current, while the dislocation density decreases. With the increase in welding current, the mechanical properties of the welded joint first improve and then deteriorate, with lower elongation observed at both lower and higher welding currents. High-cycle fatigue tests were conducted on welded joints at welding currents of 170 A and 180 A. Under high-cycle conditions, there were more fatigue striations, and impurities within the welded joint were identified as the primary cause of fatigue fracture.