Abstract: A CO2 laser-metal active gas arc welding(MAG) hybrid welding technology is used to weld the high strength steel. The effects of in situ TiC on microstructure and properties of welded joints are investigated. Results indicate that microstructure can be refined by TiC particles. The overall performance of high strength steel welded joints has been greatly improved. When the wCNT∶wTi=15%, the upper center part of the weld is composed mainly by dendrites. The average width of secondary dendrite is 8.4 m. The bottom of weld is composed mainly by large numbers of small equiaxed. When the wCNT∶wTi=0%, the upper center part of weld is mainly composed by large numbers of columnar grains. The average width of the columnar crystal is 13.25 m. The bottom of weld is mainly composed by large numbers of small columnar grains. The study on fracture shown that, there have been a large amount of small dimples in the wCNT∶wTi=15%. It is mainly ductile fracture for welded joint. But it is mainly brittle fracture and ductile fracture for welded joint of no powder. Known by the mechanical testing that the impact of energy and bending energy have been significantly improved for the weld of high strength steel in situ TiC, but it has little effect on tensile strength.

Key words: laser-arc hybrid welding, mechanical properties, microstructure