Research On Optimization Of Laser Welding Process For Ferritic Stainless Steel

In this paper,several different welding tests were designed for laser welding of 441 ferritic stainless steel.The microstructure and mechanical properties of the welded joint have been analyzed and tested.The thermal cycle curve and other data have been obtained by numerical simulation.The response surface method was used for reasonable prediction,which can provide theoretical guidance for practical production.The temperature field and stress field of laser welding of ferritic stainless steel were simulated by SYSWELD software.The shape of the weld pool,the temperature cycle curve of the node and the temperature distribution nephogram were obtained by selecting the appropriate heat source.The influence of different process parameters on the temperature field and stress field was analyzed.The distribution of residual stress was consistent with the experimental results.Residual stress in the weld increased with the increase of laser power and decreased with the increase of welding speed.The single factor variable test results of laser welding of ferritic stainless steel showed that with the increased of laser power,the surface quality of the weld decreases,meanwhile the waist shape was more obvious,the grain size of the weld and HAZ increased gradually,and the hardness decreased.When the laser power was 1.1k W and the welding speed was1.5m/min,the low energy density made the plate not penetrated,and the tensile sample broken in the weld the elongation at failure was 19%,and the tensile strength was 97.8% of the base metal;With the increased of welding speed,the waist shape disappeared gradually.furthermore,the grains of weld and heat affected zone were refined,the hardness was improved.When the laser power was 1.5k W and the welding speed was 2.1m/min,the plate was not penetrated,at this time,the elongation at failure was 15%,and the tensile strength was about 97.1% of the base metal.When the positive defocus amount was used,the weld was not penetrated,and the tensile sample was broken in the weld.At this time,Elongation after fracture was low,about 10.4%,and the tensile strength of the weld was 93% of the base metal.With the defocus amount from positive to negative,the weld penetration,and the grain size of weld and HAZ first increased and then decreased.The SEM analysis of tensile fracture showed that no matter the sample was fractured in the weld or the base metal,its microscopic characteristics were typical ductile fracture.A large number of dispersed second phase particles were found in the center of the dimples.By EDS analysis,the second phase particles were chromiun carbides.In the range of the optimal parameters obtained from the single factor variable test,the response surface method was used to optimize the parameters.Taking the average value of melting width of multiple groups of tests as the optimization objective,the optimal laser welding process parameters were obtained: laser power 1500 W,welding speed 1.6m/min,defocus amount-1.2mm.Then used the optimized parameters for the verification test,theweld was well formed,weld hardness was 1.3 times of the base metal.At this time,the fracture position of the tensile test was located in the base metal,which proved that the tensile strength of the joint was better than that of the base metal.