| Austenitic stainless steel SUS301 L has become the main material for making railway trains,because of its good anti-corrosion resistance,high strength,and good weldability.Filler materials were used to improve weld formation,reduce metallurgical defects and assembly accuracy during laser welding with filler wire,which was of great significance to the welding of stainless steel railway trains.In this paper 1 mm and 2 mm stainless steel was used to carry out a series of laser welding with filler wire experiments.Weld formation,microstructures and mechanical properties under different welding conditions were studied.The prediction of the tensile-shear properties were realized by numerical simulation calculation.The effects of laser power,welding speed and wire feeding speed on weld formation were studied by single factor experiment.Experimental results show that laser power,welding speed and wire feeding speed had a linear relationship with weld penetration.If increasing laser power,decreasing welding speed and wire feeding speed,weld penetration increased linearly.Weld width increased first and then decreased with the increase of laser power,and weld width increased with the increase of welding speed and wire feeding speed.The orthogonal experiment showed that the welding heat input(E)and the corresponding energy value(Q)of welding wire per unit volume should be in a suitable range(E(≥69.6 kJ/m),Q(8.5~10.0 W·min/mm3))to obtain welds with good formation quality.The feed direction,wire distance and shielding gas flow mainly affected the wire melting mechanism and metal transfer modes.More stable liquid bridge was formed and higher filler wire melting efficiency was observed in leading feed,which resulted in better weld formation quality.At H of 0.5 mm,the transfer mode was liquid bridge transfer which was the ideal transfer mode and better weld formation was obtained.Shielding gas flow mainly affected the stability of liquid metal transition to molten pool.When the protective gas flow was too large,blowing force was large,which would affect the stability of liquid bridge transition.The effect of laser incident position(L)and laser incident angle decided the heat input distribution on the plates.Better weld formation was obtained when the incident position(L)was 0.6 mm and the incident angle was 0 degree.It was concluded that better weld formation could be obtained under condition of leading feed,wire distance H=0.5 mm,laser incident position L=0.6mm and 0 degree laser incident angle.According to the morphology of ferrite and the chemical elements in the weld,the solidification mode of the weld was FA mode.The phase composition in the weld was austenite and ferrite(about 10%).The hardness of the base metal area was the highest,with an average of 272.0 HV,followed by 226.7 HV of weld zone,and the minimum microhardness of HAZ was 208.0 HV.The fracture was always located in the weld where the thickness of it was the smallest.There was a linear relationship between weld width and tension shear force(F=6.23102c+12.27993,c was weld width).The weld width can be the basis for judging the tensile-shear force,under the condition of good weld formation quality.Its fracture mode was mainly ductile fracture with obvious fracture surface dimples.Combination of planar gauss heat source and homogeneous body heat source was established.The weld pool was approximately circular with dense isotherms in front,with large temperature gradient,and sparse isotherms in back with relatively small temperature gradient.The numerical simulation results of node temperature curve were in good agreement with the measured results.With the change of laser incident position and laser incident angle,the trend of simulation results of weld cross-section size was similar to that of actual weld cross-section size.The maximum error of weld width and penetration was 5.65% and 7.26% respectively,and the error was within acceptable range. |
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