Effect of Welding Thermal Cycle on Microstructure and Mechanical Properties in Multi-pass Submerged-arc Welding

To research effect of welding thermal cycle on the microstructure and mechanical properties of welded joint, two pieces of 60mm thick plates were welded together using automatic submerged-arc welding (SAW) method with suitable welding parameters. After 17 passes welding, the microstructures and phases of the welded joint was carefully observed and analyzed by using a Carl Zeiss optical microscope in different zones of welded joint, and the surface micro-hardness of the welded joint was measured systematically by using microscopic-hardness tester Lycra. Afterwards, the mechanical properties of the weld metals were measured through stretching. Through a series of measurements and observations, the welding experiment results indicate that effect of welding thermal cycle on the microstructure and mechanical properties of welding joint is great, the grains of the bottom of the weld metal are certainty smaller and more uniform, and the bottom of the weld metal have more excellent mechanical properties.