Production Process Optimization Of Precision High Frequency Straight Seam Welded Pipe

Precision high frequency straight seam welded pipe has the advantages of high dimensional accuracy,high surface quality and low cost.It is widely used in automotive,marine,aerospace and other fields.However,the welded pipe produced by induction welding still has some defects in quality.The key to improving product quality depends on the continuous optimization of production process.Therefore,it is great practical significance to optimize welding process and heat treatment process for precision high frequency straight seam welded pipe.In this paper,the Q235 B high frequency straight seam welded pipe is taken as the research object,and its welding process and heat treatment process are optimized by combining numerical simulation technology with experimental research.Firstly,the influence of process parameters such as opening angle,exciting current,welding frequency and billet thickness on the welding quality is analyzed by numerical simulation technology,and the optimum welding process parameters are determined by combining the orthogonal test design.The welding pipe is trial-manufactured using the optimum welding process parameters.The raw material(steel strip)of the welded pipe needs to be inspected for its performance before the test-manufactured pipe is manufactured.The performance of the trial-manufactured welded pipe is tested and the accuracy of the numerical simulation is verified.Finally,the welded pipe is normalized and the optimum heat treatment process is explored to optimize the performance of welded pipe and further improve the quality of welded pipe.The main research results are as follows:The numerical simulation results show that the increase of opening angle and billet thickness will result in the decrease of magnetic induction strength and current density on the billet,which will decrease the peak temperature at V-point of the billet.Increasing excitation current and welding frequency will result in increasing magnetic induction and current density on the billet,which will increase the peak temperature at point V of the billet.Excessive or low peak temperature at V-point of billet will reduce welding quality.Through range analysis of orthogonal test design,the optimum level combination of welding process parameters is determined as A4B1C1D4,the opening angle is 7°,the exciting current is 1250 A,the welding frequency is 175 k Hz,and the thickness of the billet is 2mm.At this time,the residual stress at V-point of the billet is 231.24 MPa,and the residual stress along the circumference of the welded pipe decreases gradually.Variance analysis shows that the influence of billet thickness on residual stress of weld is highly significant,that of opening angle and welding frequency is significant,and that of exciting current is significant.The test results show that the main chemical composition(mass fraction)of the steel strip is 0.140%C,0.017%Si,0.451%Mn,0.017%P,0.011%S,the tensile strength is418.17 MPa,the elongation is 36.53%,which meets the requirements of production quality of welded pipe.The performance test of welded pipe shows that the tensile strength and elongation of welded pipe are 461.10 MPa and 52.30%,and the tensile fracture mode is ductile fracture.Moreover,the number of dimples at the fracture surface is large and the size is small and deep.No fissures or cracks were found in the flattening test of welded seam of welded pipes at 0°and 90°.The microstructures at the weld seam are widmanstatten structure with maximum microhardness of 208.57 HV,ferrite +lamellar pearlite at the base metal and 157.50 HV at the minimum.The normal and tangential residual stresses at the weld seam are 257.70 MPa and 20.50 MPa,and the residual stresses decrease gradually along the circumference of the welded pipe.The optimum heat treatment process for welded pipes is 900℃×10min,the widmanstatten structure disappeared in the microstructure of the weld,which was ferrite + flaky pearlite.The hardness,normal residual stress and tangential residual stress at the weld were reduced by 31.90%,12.38% and 12.68% respectively.50 pictures,14 tables,85 references.