Hybrid laser welding of dual phase steel DP600: Microstructural and mechanical properties

Abstract

The desire to combine the high productivity of laser welding with the robustness in terms of joint preparation of the GMAW process constitutes one of the main reasons for the increasing interest in the hybrid laser welding (HLW) process. In the present study, DP600 advanced high strength steel sheet, with a ferritic-martensitic microstructure and a thickness of 1,4 mm, was subjected to both CO2-laser/GMAW and diode pumped Nd:YAG-laser/GMAW hybrid laser welding. The selection of adequate filler metal and heat input with respect to weld metal and HAZ strength matching is discussed. A comparison of the resulting microstructure and mechanical properties obtained with both hybrid laser welding processes, as well as autogenous laser welding and GMAW welding, is made. It was found that a hardness drop might occur in the HAZ due to tempering of the martensite in the base material microstructure, leading to strength decrease and localized deformation during tensile testing. On the other hand, use of inappropriate filler material in combination with low heat input might lead to excessive weld metal hardness. In a second stage, the weld gap bridging ability of the HLW process is measured and compared to that obtained in laser welding.The desire to combine the high productivity of laser welding with the robustness in terms of joint preparation of the GMAW process constitutes one of the main reasons for the increasing interest in the hybrid laser welding (HLW) process. In the present study, DP600 advanced high strength steel sheet, with a ferritic-martensitic microstructure and a thickness of 1,4 mm, was subjected to both CO2-laser/GMAW and diode pumped Nd:YAG-laser/GMAW hybrid laser welding. The selection of adequate filler metal and heat input with respect to weld metal and HAZ strength matching is discussed. A comparison of the resulting microstructure and mechanical properties obtained with both hybrid laser welding processes, as well as autogenous laser welding and GMAW welding, is made. It was found that a hardness drop might occur in the HAZ due to tempering of the martensite in the base material microstructure, leading to strength decrease and localized deformation during tensile testing. On the other hand, use of inappropriate ...