Thermal cycle and microstructure of backing weld in double-sided TIG arc horizontal welding of high-strength steel thick plate

Double-sided arc horizontal welding is a new process for high-strength steel thick plate. This study aims at studying thermal cycle and microstructure of backing weld. The special heating cycle with two peaks in double-sided double-arc welding is beneficial to the generation of microstructure with good strength and toughness, due to the effect of preheating and postheating. The microstructure was a mixture of ferrite and lath martensite. The heat-affected zone (HAZ) in the root area was overheated, owing to the shape of groove in the horizontal welding, resulting in meshes in the grain boundary. The meshes were analyzed to be the tempered martensite. Hardness tests showed that there were some softened regions in the HAZ on account of high-temperature tempering.