| SUS301L stainless steel is an austenitic stainless steel,which is extensively used in rail vehicles,mechanical electronics,light industry and other fields.When welding SUS301 L stainless steel using conventional welding methods such as tungsten gas shielded welding(TIG),molten electrode inert gas shielded welding(MIG),molten electrode active gas shielded welding(MAG),resistance welding,plasma welding,etc.,defects such as hot cracks,coarse grains and welding deformation are more likely to occur.At present,the roof of the subway is often made of SUS301 L stainless steel corrugated sheet.The welding method is resistance spot welding.The main problems are large deformation of the plate after welding,poor sealing of the welded joints,weak tensile and fatigue strength of the joints,and low efficiency.In order to solve these problems,laser welding technology is used to weld corrugated board of subway roof in this thesis,and simulation and experimental research are carried out on SUS301 L stainless steel non-penetrating laser lap welding for subway roof,which aims to give full play to the advantages of fast welding rate,small deformation after welding and good joint sealing.(1)Numerical simulation on laser overlay welding temperature field of SUS301 L stainless steel.The heat transfer model of laser stack welding of SUS301 L stainless steel is established,the numerical simulation of the welding temperature field is carried out.Meanwhile,the area change rate is used as an auxiliary parameter to evaluate the amount of plate deformation.The influence of various welding process parameters on the weld surface morphology is studied,and the suitable range of process parameters is determined: laser power is 950W?1050W,welding speed is36mm/s?40mm/s,defocusing amount is 0?2mm,the flow rate of shielding gas is20?30L/min.(2)Single factor and orthogonal welding experiment analysis.A single factor experiment on the progress parameters is conducted to determine the suitable range through numerical simulation.The influence mechanism of the welding process on the macroscopic appearance of the weld is experimentally studied,and a significance analysis of the influence of each process factor on the welding quality is carried out.As a result,the process parameters are optimized.Finally,these optimized process parameters are used to the non-penetrating laser stack welding of the SUS301 L stainless steel sheet for the roof of the subway.The welding quality meets the requirements.(3)Result analysis on laser welding of SUS301 L stainless steel and detection of the micro-structure and performance of the joints.In order to evaluate the effect of the orthogonal experiment,the macro-morphology,and micro-structure of the joints are observed,and EDS,micro-hardness and mechanical properties of welds obtained under optimized process parameters are tested.The results show that the surface of the weld is silver-white and continuous;the weld area is consisted of equiaxed and columnar crystals,and the heat-affected zone is mainly consisted of roughened equiaxed crystals.The micro-hardness of each area of the weld is less than that of the base material,and the tensile strength of the weld is 2599.96 k N.Compared the simulation results with the experimental data,the errors of both the weld width of the upper plate and the weld depth of the lower plate are within 2%,which proves that the established laser welding heat transfer model is correct.In this thesis,the theoretical and experimental research on the laser stack welding of 0.6mm thick SUS301 L stainless steel is carried out,in which the simulation is not only used to guide the experiment but also verified by the experiment.The research purpose of this thesis is to provide an alternative welding method with higher efficiency,better sealing and higher tensile and shear strength for the welding of stainless steel corrugated plates for subway roofs. |
PDF Full Text Request