| The 304 stainless steel was chosen as connection object,with the goal of in-situ synthesis of Fe-Mn-Si shape memory alloy weld microstructure.Through the design of adding powder composition and the optimization of laser processing parameters,the 304 stainless steel welding joint which possessed Fe-Mn-Si memory alloy weld microstructure was obtained by CO2 laser welding system,its mechanical properties and structure property were studied.The laser power,welding speed and defocus were selected as three main process parameters,and the single factor test method was using to analyze the influence of process parameter on the formation of Fe-Mn-Si memory alloy welding joint by laser powder.The results showed that the heat input of welding joint changed with process parameters,while it affecting the width,ingredient,tensile strength and hardness of welding joint.According to the single factor test results,the tensile strength was chosen as the test index to conduct orthogonal test.By range analysis and variance analysis,the results showed that optimum technology parameters for 2 mm thickness 304 stainless steel plate laser powder welding test were:P=2.7 kW,v=160 mm/min,z=5 mm,the tensile strength of welding joint was 745.4 MPa,reaching 95%of the tensile strength of base metal(751 MPa);Fe-Mn-Si memory alloy welding joint were well formed,and the microstructure from 304 stainless steel base metal to weld center was austenite,plane crystal,cellular dendrite,dendrite and axialite in turn.In order to achieve the aim of in situ synthesis of Fe-Mn-Si shape memory alloy weld microstructure by laser welding with powder filling,the uniform mixing design method was adopt to get the regression equation between the matching of Fe/Mn/Si/Cr/Ni powder and the weld joints structure components.The average micro hardness inside the Fe-Mn-Si memory alloy welding joint area was HV 242.8,which was higher than 304 stainless steel weld hardness.The reason was that there were martensite structure with higher hardness within Fe-Mn-Si memory alloy welding joint,and there were more Mn and Si in welding area which contributes the improvement of hardness;the tensile strength and bending fatigue properties were obviously better than 304 welding joint,the strain fatigue strength under 6%deformation achieves 90%of base metal;the residual stress of Fe-Mn-Si memory alloy welding joint was relatively lower than 304 stainless steel welding joint.The results showed that Fe-Mn-Si memory alloy welding joint has better mechanical properties.Fe-Mn-Si memory alloy welding joint has significant shape memory effect.Fe-Mn-Si memory alloy stress induces ???? martensite reverse transformation and the compatibility of deformation is the basic reason to reduce the residual stress of welding joint and improve the fatigue strength of welding joint. |
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