Investigations On Welding Residual Stress In Austenitic Stainless Steel Joints By Means Of Numerical Simulation

Austenitic stainless steel is one of the important engineering materials, becoming widely used in nuclear power and engineering machinery and equipment in recent years. Welding is an important processing technology for austenitic stainless steel. In the process of welding, the non-uniform temperature field, will inevitably produce welding residual stress and deformation. In general, welding residual stress field depends on several main factors including material properties, structure demensions, external constraints and welding thermal process. Studies have shown that both welding residual stress and distortion have negative influences on the static strength, fatigue strength and structural stability and manufacturing precision. In addition, welding residual tensile stress is one of the important reasons that leads to stress corrosion cracking of alloy welded structure. Therefore, how to accurately predict and evaluate the welding residual stress in structure has become a research topic of concern.Austenitic stainless steel is easy to work hardening. In the welding process, weld and its vicinity undergoes a number of thermal cycles, making this part of metal to produce a certain degree of plastic deformation and subsequently work hardening. At the same time, work hardening of metal will be eliminated in the heating process due to recovery, recrystallization and grain growth, so in order to accurately predict the residual stress of austenitic stainless steel welding joint, both the work hardening and annealing effect have to be taken into account in the material constitutive relations.In this paper, based on ABAQUS software, a computational approach was developed to simulate welding temperature field and residual stress distribution for austenitic stainless steel multi-pass joint. Using the developed calculation method, the influences of work hardening and annealing effect on calculation accuracy of welding residual stress were clarified, the numerical simulation results were verified by experimental methods. In addition, on this basis the welding residual stresses of austenitic stainless steel SUS304 plate repair welding and austenitic stainless steel dissimilar steel pipe were predicted by the numerical simulation.The results show that: 1) For austenitic stainless steel SUS304 welded joints, the simulated residual stress is higher than the measured value in the case of taking into account of work hardening without consideration of annealing effect. Therefore, annealing effect needs to be taken into account in the numerical model. With the increase of annealing temperature, the peak longitudinal residual stress increases and the high stress area is also expanding. In this study, effects of annealing temperature on the transverse residual stress is very small. The annealing temperature is set to 1000℃, the calculated longitudinal residual stresses are relatively close to the measured values. 2) The simulated stress in the case without consideration of work hardening is significantly less than the experimental value, therefore, in the calculation of austenitic stainless steel welding residual stress, it is necessary to consider the work hardening of the material. In addition, isotropic hardening model will overestimate the welding residual stress, kinematic hardening model will underestimate the welding residual stress, and the mixed hardening model can be used to accurately predict the welding residual stress compared to the other two hardening model. 3) Repair welding process will redistribute the original stress field. For the longitudinal residual stress, the residual stress value will increase. For the transverse residual stress, tensile stress values will increase, compressive stress values will decrease. 4) For austenitic stainless steel pipe joint, Axial and circumferential residual stress of the weld metal and its vicinity is very large. However, radial stress distribution is flat, and the peak stress value is rather small. For girth welding joint, welding residual stress distribution in the welding start-finish location is different and more complex than other location.