Research On CO₂Laser Welding Proeess Of DP590Cold-rolled Dual Phase Steel And Microstructure And Properties Of The Welded Joints

With the energy crisis and environmental problems increasing，Lightweight,energysaving, environmental protection and safety vehicles are becoming the main developmentdirection of the automotive industry.As one of the most typical products of new advancedhigh strength steel (AHSS) series,dual-phase steel has the advantages of lower cost, higherinitial work hardening, lower yield ratio,higher strength,better ductility and has no agingphenomenon at room temperature.During use Process,it can increases the strength ofautomotive components to meet the security requirements, also make the car to reduceweight and reduce fuel consumption, in the manufacturing process, also improve the bodysteel processing behavior, So it has been widely used in the field of automobilemanufacturing.With the increasingly widespread application of dual steel, its welding problemsquickly became increasingly prominent problems to be solved of automotivemanufacturing industry. Dual steel arc welding, resistance welding and other weldingmethods exist heat-affected zone grain coarsening,the heat-affected zone softening, andhardened tissue cold cracking tendency problems, directly affect the quality of weldedjoints.In this paper, for dual steel welding problems above, laser butt welding experiment of1.5mm thick cold-rolled dual-phase steel DP590was carried out by using theGS-TFL-6KW-type cross-flow CO2laser. Investigated the influence of weld forming,microstructure and properties of welded joints on laser welding process and the jointscorrosion resistance.Metallographic analysis showed that: Weld crystallization morphology was dendriticmorphology, grain was smaller compared with the base metal, the coarse-grained range ofheat affected zone was small,soft zone was narrow. Weld tissue mainly consisted of lathmartensite, bainite and residual austenite.Welding power, welding speed had significantly influence for microstructure andmechanical of DP590joints. Reduced heat input and cooling rate of the accelerationprovides greater degree of super-cooling, resulted in nucleation rate increasing, grainrefinement, the weld and heat affected zone width decreasing, softening zone becomingnarrow,martensite increasing, and the uneven distribution of weld tissue. Organized changed under different laser processing did not affect the tensile strength of welded joints,but the resulting weld hardness slightly increasing, the joint forming ability decreasingcompared with the base material.Polarization curves analysis of electrochemical corrosion tests showed that the weldcorrosion resistance for the three welding process was better than the base material, dualsteel laser weld corrosion resistance can meet production requirements.Through above study, the foundation of laser welding process selection andassessment was established for cold-rolled dual-phase.