Research On Laser Welding Process Of High-strength Steels DP1000and Spectroscopic Analysis Of Laser Welding

This paper mainly studied Nd: YAG laser welding technique of DP1000highstrength dual-phase steel sheets, and the mechanical properties and metallurgicalbehaviors of butt welded joints were analyzed. Besides, the welding quality waspreliminarily detected by spectroscopic of the laser plasma which was generated bylaser welding.Laser welding process of DP1000was developed by the method of the firstsurfacing welding and the second butt welding. The high-quality of weld seam can beobtained.by a large number of welding experiments, under1700W laser power,6~10mm/s welding speed,-1mm defocusing distance and20L/min of shielding gas.Additionally, the experimental results indicated the laser welding mode was mainlyheat conducting welding under1500W laser power, and that was deep penetrationwelding under1700W laser power.The macrostructure analysis showed that the heat affected zone(HAZ) of weldedjoint included overheated zone, partial phase transformated zone and tempered zone,of which the overheated zone was the closest to FZ and tempered zone was thefarthest. The investigation showed that the microstructure in fusion zone(FZ) wasthick lath martensite, upper bainite, residual austenite and pro-eutectoid ferrite, whilethe microstructure in overheated zone was thin lath martensite, and that in other zoneswere tempered martensite and ferrite, which caused the welded joint softening. Also,the soft zone has been found through microhardness measurement. The longitudinallyand transversely tested weld specimens showed higher strength and elongation of thelongitudianal weld specimens. Moreover, the process of the transverse test showedthat almost all plastic deformation occurred in the heat affected zone. The failure ofwelded joint was ductile fracture, and dimples and particles were observed on themicro-fracture surface.Spectroscopic analysis of laser welding revealed that spectral intensity andelectron temperature didn’t change as laser power was1700W and welding speed wasdecreased. Oxidation and misalignment of weld seam resulted in fluctuation of theelectron temperature and instability of laser welding processes. Additionally,oxidation caused spectral intensity and electron temperature slightly increasing, whileweld seam misalignment caused slightly decreasing.