The Laser Surface Treatment Of High-strength Steel Welded Joints And The Study Of Properties

Laser-arc composite welding of high strength steel has been widely used in industrial production.However,corrosion and fatigue cracks often occur in welded joints of high strength steel,and these phenomena usually begin on the surface.In this study,the surface of the welded joint of high strength steel was treated with Nd:YAG solid state laser,and the properties of the welded joint after heat treatment were studied.Based on the Visual-Environment software platform,the Gauss surface heat source model is used to simulate the single channel scanning and multi pass process of high strength steel surface heat treatment.The suitable process parameters of laser heat treatment are selected to analyze the temperature field in the simulation process.At the same time,the Nd:YAG solid state laser is used to heat the sample with the same technological parameters as the numerical simulation,and the results are compared with the simulation results.The results show that the hardened layer which is consistent with the actual laser welded joint morphology can be obtained,and the rationality of the simulation model is verified.Through the prediction of the simulated hardened layer,the laser surface heat treatment experiment on the welded joint of high strength steel is carried out by selecting three groups of parameters,which are laser power,speed and lap rate as variables.The electrochemical corrosion test of the original and the surface treated samples on the weld area is conducted on the same area.The results show that low corrosion current and high polarization resistance have been obtained by the laser surface treated welded joint,and the corrosion resistance of the sample is improved,the lower laser power which is about 0.8kW,the higher laser scanning speed which is 1.4m/min,lower lap rate which is 10%,the corrosion resistance are better in the parameters of each group.The hardness and tensile tests of the best corrosion resistant specimens were carried out.The hardness test results show that the hardness of the surface after the laser surface treatment is obviously improved,and the hardness of the softening area is the highest and the hardness distribution of the weld zone is more uniform.The tensile test results show that the untreated welded joints are mainly brittle fracture,the tensile strength is low,and the surface after the surface treatment is treated.The martensitic structure of the variable zone is refined,thus the toughness of the welded joint is improved and the tensile strength of the specimen is improved,and the higher the hardness of the phase transition zone of the welded joint is,the toughness is relatively reduced,so the tensile strength is relatively lower.