| 12Cr1MoV steel has good heat resistance,high oxidation resistance,excellent corrosion resistance,well welding properties,and is widely used in the field of power plant pipelines.The power plant pipelines are exposed to harsh environments such as high temperature and pressure for a long time,and the organization of the materials will inevitably undergo changes,leading to a decrease in mechanical properties,resulting in pipeline rupture and affecting the normal operation of the power plant.If a pipeline fails,it is necessary to weld and repair the cracked pipeline.The welding process can cause a certain degree of damage to the original structural performance of the steel,and residual welding stress can seriously affect the strength and performance of the material,shorten the service life of the equipment,and cause safety hazards.Firstly,Finite element simulation software Abaqus was used to simulate a12Cr1 Mo V steel pipe with an outer diameter of 159 mm and a wall thickness of 6 mm.Conduct simulation experiment was single layer and single channel.Deformation nephogram and residual stress distribution of welded pipe were obtained under welding current of 120 A,welding voltage 20 V and welding speed of 60 mm/min.The results show that under these parameters,there is basically no deformation in the butt welding of 12Cr1 Mo V steel pile,and the Mises stress generated by welding is 349.6～380.0 MPa.There is also stress concentration in the weld seam and its heat affected zone.Finite element analysis software Abaqus can effectively analyze the welding process of12Cr1 Mov steel pipe.Secondly,Multi-layer and multi-pass welding with argon arc welding was adopted to butt welding of 12Cr1 Mo V steel pipe with an outer diameter of 159 mm and a wall thickness of 24 mm.Mises stress distributions under different welding currents(100,120 and 140 A)and welding voltages(16,20 and 24 V)were simulated.The optimal welding parameters are voltage 20 V,current 120 A,and the Mises stress generated by welding is 390～430 MPa.The paper provides the welding thermal cycle curve of a specific part under this parameter,and the deviation from the actual welding process is less than 10%.Finally,Multi-layer and multi-pass welding was used in 12Cr1 Mov steel with Vshaped grooves under the parameters of welding current 120 A,welding voltage 20 V,and welding speed 60 mm/min.After welding,ultrasonic and magnetic particle testing showed that the ultrasonic results in the weld area were uniform,and no excessive defects were found.There were no obvious welding defects on the surface and inside of the weld,and the welding quality was qualified.The maximum residual stress near the weld seam is 346.21 MPa,which is consistent with the simulation results of finite element analysis software Abaqus.To further improve the quality of the weld seam,hydrogen dissipation heat treatment and post weld heat treatment on the weld seam were conducted.The hardness distribution,tensile properties,bending properties and impact properties of the 12Cr1 Mo V weld seam after welding and heat treatment were tested and analyzed using a microhardness tester,electronic universal testing machine and impact testing machine.The microstructures of the 12Cr1 Mo V raw material,weld seam after welding and heat treatment were observed using optical microscopy.The morphologies of these materials impact fracture and tensile fracture were tested by scanning electron microscopy.It was found that the microstructure of 12 Cr Mo V raw material is pearlite,ferrite and tempered bainite,which is a typical pearlite heatresistant steel.After welding,lath ferrite,acicular ferrite,martensite and bainite appear around the 12Cr1 Mo V weld,which makes the hardness difference larger,the impact absorption energy is lower and the comprehensive performance of the weld is reduced.After weld seam heat treatment,the martensite appearing around the 12Cr1 Mo V weld seam is transformed into tempered sorbate,making it closer to the raw material microstructure and properties of 12Cr1 Mo V.The SEM morphologies of the impact and tensile fracture surfaces show a larger number of dimples,indicating that the samples have good plasticity and toughness,further indicating the improvement of weld quality by heat treatment after welding.This thesis has 52 figures,18 tables and 111 references... |
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