Effect of interpass temperature on the microstructure and mechanical properties of multi-pass weld metal in a 550-MPa-grade offshore engineering steel

摘要

The influence of interpass temperature on the microstructure and mechanical properties of multi-pass weld joints (up to 36-mm thickness) by submerged arc welding (SAW) was studied from the perspective of offshore engineering. Optimal mechanical properties were obtained with the interpass temperature of similar to 130 degrees C. Decreasing interpass temperature from 130 to 80 degrees C increases the strength and hardness at the cost of impact toughness of the weld joint due to the formation of hard phases including bainite and martensite. Increasing the interpass temperature from 130 to 250 degrees C promotes a larger volume fraction of coarse M-A constituents and larger inter-spacing of high-angle boundaries, which, in turn, deteriorates the toughness. In addition, a large amount of MA constituent necklacing prior austenite grains was observed in the reheated zone of all weld metals and was responsible for the low impact energy of the weld joint.