Microstructure and Low Temperature Toughness of Weld Joints Prepared by Double-sided Submerged Arc Welding for Low Carbon Bainite Steel

Abstract

The low carbon bainite steel was welded by double-sided submerged arc welding and the microstructure and low temperature toughness of the joints was studied by optical microscope and PSW750 instrumented impact testing machine. The results show that the microstructure of the weld seam consisted of acicular ferrite and granular bainite, however the HAZ shows a microstructure consisted of bainite ferrite and granular bainite. The hardness at HAZ near the weld bond is the highest and then decreases gradually approaching to the hardness of base metal. In comparison to the matrix the weld seam and HAZ show a lower toughness with a ductile brittle transition temperature at-20℃and-60℃ respectively, which may be ascribed to the occurrence of solidification segregation, highly concentrated dislocations and formation of carbon nitrides of alloying elements such as Ti and Mo at grain boundaries etc.in the weld joints during rapid cooling after welding.