Welding Numerical Simulation And Microstructure Property Analysis Of Pipe Body Arc Fillet Weld

Rotary drilling rig is a kind of engineering machinery and equipment used for taking soil and filling piles into holes,which is widely used in the construction of urban transportation,railroad bridges and other foundation projects.As the core component of rotary drilling rig,the drill pipe is prone to failure resulting in large economic loss due to its complicated force in actual work.Drill pipe body and external key bar are welded with dissimilar steel and are widely used in various complex and harsh working conditions because of their excellent comprehensive performance.However,the difference in the composition and properties of the welded material can cause large residual stress and deformation after welding,which can greatly reduce the quality of the welded joint.Therefore,it is of great significance to study the residual stresses and deformations in the welded arc fillet welds of drill pipe bodies and external key bars and to evaluate the comprehensive performance.In this thesis,the arc fillet weld between the drill pipe body and the external key bar is the object of study.Based on the actual welding conditions and process parameters,numerical simulations are carried out using Marc software to study the combination of welding materials,welding sequences and structure size combinations on the residual stress and welding deformation of the arc fillet weld.The results show that the welding residual stress and deformation are mainly concentrated at the weld seam,and the maximum residual stress values are in the fusion zone on both sides of the arc fillet weld.Comparison of six welding material combinations,HG850 and20 Cr Mn Ti combination,HG850 and 30 Cr Mn Ti combination of residual stresses and deformation at the weld seam is smaller.Through the optimization of the welding sequence,the maximum reduction of the axial residual stress value of the arc fillet weld between the tube body and the single key bar is about 24.2%,and the maximum reduction of the welding deformation is about 28.6%;the maximum reduction of the axial residual stress value of the arc fillet weld between the tube body and the multiple key bars is about 41.6%,and the maximum reduction of the welding deformation is about 55.6%.The residual stress and deformation of fillet weld in the arc of the drill pipe body varied significantly for six different combinations of sizes.The weld residual stress is higher when the pipe diameter is 200 mm,smaller when the pipe diameter is420 mm,and the overall weld deformation is smaller when the pipe diameter is 200 mm and 320 mm.Weld residual stress increases with the increase in wall thickness of the tube body and gradually decreases with the increase in the height of the key bar.Finally,through the thermodynamic and kinetic simulations of the welded material,the microstructure distribution and phase transition regulation under different conditions are obtained.The microstructure of the welded base material is ferrite and tempered sothite.The weld is a coarse columnar crystal at the weld,which is organized as ferrite and pearlite.A partially martensitic structure appears in the heat-affected zone,which increases the hardness and strength of this region.The microstructure of the welded base material,weld microstructure and both sides of the fusion zone microstructure after the parcel heat treatment did not change,but the microstructure became more uniform.Tensile tests showed that the strength of the different welded joints were between the base material of the weld and the wire.Microhardness tests in different areas showed the lowest hardness at the weld seam and the hardness in the fusion zone on both sides increased due to the appearance of partial martensite structure.The strength and elongation of the welded joint between HG850 and 20 Cr Mn Ti increased significantly in the transverse direction after heat treatment,while the strength and elongation of the longitudinal direction of the weld showed a small decrease after heat treatment.The strength and elongation of weld seam transverse and longitudinal of HG850 and 30 Cr Mn Ti welded joints showed a small decrease after heat treatment.The hardness of the weld base material and the weld seam decreased after heat treatment,while the hardness of the fusion zone on both sides of the weld seam increased.The thesis has 72 pictures,9 tables,and 79 references.