Effect of Welding Heat Input on Microstructure and Mechanical Properties of HSLA Steel Joint

Abstract

Gas tungsten arc welding of HSLA steel was conducted with different welding heat inputs, and the influences of welding heat input on the microstructure, Vickers hardness, and impact toughness of heat-affected zone (HAZ) in prepared joints were systematically investigated. The microstructure in HAZ with low welding heat input mainly consisted of martensite, and the microhardness of coarse grain HAZ was measured higher than that of fine grain zone. The results show that increasing the welding heat input could suppress the formation of martensite and reduce the microhardness of HAZ. However, the impact toughness of HAZ was not monotonously improved with the increase of welding heat input. It is deemed that the coarsened grain, the formation of upper bainite, and the non-uniform distribution of carbides and inclusions in HAZ could degrade the impact toughness. Tests demonstrate that the optimum comprehensive properties of HAZ were obtained when the welding heat input was 0.67 kJ/mm.