Effect Of Heat Treatment On Residual Stress And Mechanical Properties Of 12Cr1MoV Steel Pipe Welded Joint

After the welded joint undergoes multiple welding thermal cycles with different peak temperatures,it will lead to a diversity of metallographic structure and mechanical properties in this area.Because the working conditions of power plant pipeline components are very bad,it is necessary to transport high-temperature and high-pressure steam,but also to withstand the high-temperature effect of flame and smoke,pipeline welded joints become a weak link.12Cr1MoV is a low-alloy pearlite heat-resistant steel with good oxidation resistance,thermal strength,corrosion resistance,and welding performance.This article takes 12Cr1MoV steel pipe weldment as the research object and uses the combination of test and simulation to analyze the changing characteristics of the temperature field,stress field,and mechanical properties of the welded joint during the welding and heat-treatment process.Optimization provides a reference basis.The main research work and conclusions of this article are as follows:(1)Research on residual stress simulation method of 12Cr1MoV steel pipe welding joint after welding.The comparative analysis uses the simulation results of the double ellipsoid heat source model,the uniform density volume heat source model,and the 3D geometric model and 2D geometric model.Finally,the 3D uniform density volume heat source model with more accurate calculation and less time-consuming calculation is selected Finite element calculation.The method of combining experiments and finite element simulation is used to study and analyze the accuracy of the finite element simulation temperature field.The real-time temperature data of the actual welding process is collected by the dynamic data collection and analysis system,and compared with the simulated temperature field results.The results show that the experimentally measured values are in good agreement with the simulated values,proved the reliability of the temperature field simulated by finite element.(2)Study the influence of heat treatment process on the thermal stress during welding of 12Cr1MoV steel pipe.Based on the thermo-elastoplastic model,the finite element software ABAQUS was used to establish the butt joint welding model of 12Cr1MoV round pipe,and the sequential coupling finite element analysis program for welding residual stress was established.Simulate the processes of preheating before welding,welding heat input,hydrogen elimination treatment and tempering heat treatment after welding.And analyze the change law of residual stress.The indentation stress tester is used to measure the residual stress distribution of the welded steel pipe in different states and compare it with the simulation results.The results show that the simulated value of the hydrogen elimination treatment residual stress is consistent with the test result,and the error is within 10%.At the same time,it was found through research that the heat input of the secondary weld bead will increase the thermal stress in the previous weld bead.Stress has a greater influence,which can effectively reduce welding residual stress.(3)Study the effect of heat treatment process on the microstructure and mechanical properties of 12Cr1MoV steel welded joints.Using standard specimens and microplate specimens,the changes in the tensile properties of the welded joints under different heat treatment conditions at room temperature and high temperature were studied and analyzed.Observe the tensile fracture morphology and metallographic samples of the welded joints,and study the microstructure distribution and changes of the welded joints in different states.The results show that the microplate sample can accurately measure the yield strength and ultimate tensile strength of the material,but the measured value of the elastic modulus is quite different from the standard sample.At room temperature,the tensile properties of the 12Cr1MoV weld material are better than the base material,but as the temperature increases,the tempering treatment has a greater impact on the tensile properties of the weld,making the weld material's tensile properties lower than the parent material.The fractured form of the microplate sample is closer to that of the standard round bar sample,both of which are ductile fractures,while the standard plate sample is a brittle fracture.According to the tensile results of the standard round bar specimens,it can be found that the weak positions of the welded joints after different heat treatments are located at the base material of 12Cr1MoV.