Research On Welding Residual Stress Of 403 Stainless Steel Considering Solid Phase Transformation Effects

The prediction and control of residual stresses in welded structures has always been an important part of industrial production.The finite element software was used to simulate the welding process,which provided great convenience for the prediction of the residual stress in the welded structure.However,for low alloy high strength steel with complex composition,the traditional finite element software is mostly based on the ideal elasto-plastic assumption for the calculation of the welding mechanics,and ignores the influence of the solid phase transformation on the residual stress,so its stress field calculation results are often very different from the measured value.Therefore,this paper attempts to establish a multi field coupling model to describe the phase transformation behavior of 1Cr12 stainless steel in the welding heat cycle.In addition,the relationship among temperature,microstructures,joints mechanical properties,welding residual stresses is also the chief research content of this paper.Firstly,by means of welding thermal simulation,the type of phase transition and corresponding phase transition kinetics equation of 1Cr12 stainless steel in the welding thermal cycle are determined,and phase transformation strain mathematical model is also derived.The yield strength of the base metal,the high temperature austenite and the martensite at different temperatures is obtained by the high temperature tensile experiments.Based on the assumption of the equal plastic strain,the proper normalization function is obtained to describe the mechanical properties of the mixed phase in the phase transition process.The hardening parameters of different hardening models are obtained by fitting the true stress-strain curves of the base metal at different temperatures,and the elastoplastic constitutive equation of the hardened material is further derived.Secondly,based on the MSC.marc finite element software for secondary development,the solid phase transformation effect is incorporated into the finite element calculation,and the welding mechanics calculation is carried out for the 1Cr12 stainless steel TIG plate remelting process,and the influences of solid phase transformation effect on the evolution process of the welding residual stress are analyzed and explained.The low-temperature martensitic transformation can effectively neutralize the tensile stress in the phase transition region during cooling,resulting in a reduction of the final residual stress and even a compressive stress;the hysteresis effect of the yield strength existing in the welding cooling process can also reduce the final residual stress level;phase transformation plasticity can adjust the residual stress distribution and play a role in reducing the residual stress;strain hardening can increase the final stress level.Finally,the evolution process of residual stress under multiple thermal cycles is analyzed.It is found that the post weld bead has an obvious influence on the residual stress of the former welding path.the stress evolution process of the area close to phase transition region differs with the degree of phase transition.The area away from the second weld bead is less affected by the latter weld heat cycle.In comparative analysis of the residual stress distribution at different interpass temperature,it is found that the residual stress in the phase transition region can be reduced by increasing the interlayer temperature.When the interpass temperature is higher than the Ms of the material,the stress at weld metal and heat affected zone is lower and even compressive stress,and the stress peak appears on both sides of the heat-affected zone.