Laser-GMA hybrid welding of 960 MPa steels

Steel manufacturers are focusing more and more on developing high strength steels. This means that lower heat input welding processes are needed to achieve matching joints. The effect of the base material and the alloying of the filler materials on the mechanical properties of laser-GMA hybrid welding have been investigated. The welding trials were carried out for two ultra high strength steels, Optim 960 QC and S960QL, with different manufacturing routes. In the welding tests a butt joint was welded for both steels and the thicknesses of the base materials was 6 mm. According to the results of the welding tests, it was possible to achieve strength of the joint corresponding to the nominal strength of the base materials for both steels, regardless of the strength of the welding wire used. Matching and ductile joints were achieved for both steels with one pass and with a non-alloyed ferrite welding wire. Typically, if compared to conventional quenched and tempered steels, Optim 960 QC steel is superior with respect to the impact toughness of the fusion line and heat affected zone (HAZ) due to its low carbon and alloying contents followed by a lower hardened bainitic and martensitic microstructure. However, in this study, the toughness differences of the HAZ between the low carbon (C ≈ 0.10%) quenched and tempered reference steel S960QL and Optim 960 QC steel was not significant, but the toughness of the HAZ of Optim 960 QC was still better.