Research On Fractures Of The Laser Welding Seam Of TRIP800 During Cold Rolling

It has been technically difficult to avoid the fracture of laser-weld seams of TRIP800 during cold rolling with large reduction rates because of its high tensile strength, low plasticity, and high fragility. Therefore, the objective of this study is to improve the quality of the welding seams of the TRIP800 steel.Welding properties of the TRIP800 were investigated, including the research and development of the TRIP800 in An Steel Group, current fracture problem of the welding seams, effects of the applied Mibache welding machine on the qualities of the seams; microstructures of the matrix of the TRIP800. The major research methods include thermal simulation of the TRIP 800 welding, SH-CC diagram and its direction on welding.The results show that the Martensite, a metastable phase transferred from Austenite through non-diffusional phase transformation, is relatively more brittle. The volume of Martensite is larger than that of Austenite or Pearlite, which is the major reason for quenching stress, fracture during deformation, as well as the fracture of the welded seam. Compared to Martensite, Bainite has a better balance of strength and toughness, which offers higher wear resistance at the same hardness, so as to benefit welding. The Bainites can be obtained by setting the welding machine at a working speed of 40%, laser power of 91%, pre-heating power of 0, post-heating power of40%, by which the quality of the welding seam can be improved significantly.