Weld appearance control of ultra high strength steel in fiber laser-CMT hybrid welding process

Laser-CMT hybrid welding was used to weld 30 Cr3 SiNiMoVA ultra high strength steel sheet with the thickness of 2 mm. The melting area was measured by observing macroscopic morphology and the deformation of specimen was also recorded. The results show that,compared with laser welding,good appearance and smooth transition weld can be obtained by laser-CMT hybrid welding. In addition,the weld width of bottom part is increased,which contributes to the adaption of 1. 6 mm assembly gap and 1. 0 mm malposition under the low current condition. The thermal efficiency coefficient of CMT（ coupling with laser） is 0. 32-0. 42 by calculating welding parameters and heat input. A lateral hybrid method of laser-CMT was proposed to control the heat input. The roundness error of cylinder welded by this method is 0. 4 mm.The specimen is broken at the base metal and the tensile strength is 752 MPa.