Simulation And Experimental Study On Welding Temperature-Stress Field Of X80 Pipeline Steel

X80 pipeline steel is a high strength low alloy steel obtained by controlled rolling and controlled cooling process,which performs strong anti-corrosion and anti-fracture abilities,and it is the main material in oil and gas pipeline construction at present.Welding is the main way of pipeline connection,welding thermal cycle will destroy the excellent strength toughness combination of X80 pipeline steel,which is mainly reflected in the hardening,embrittlement and excessive residual stress of heat affected zone caused by microstructure transformation,recrystallization and grain growth,which increases the trend of cold crack and brittle fracture of X80 Pipeline steel.In view of the above problems,this paper adopts the method of combing simulation and test to carry out numerical simulation and welding test on the welding process of flat plate and pipeline,focusing on the influence of different welding process parameters on the thermal cycle parameters and residual stress of welded joint,so as to provide reference for obtaining reliable welding joint.The research contents include: the influence of welding heat input on weld pool forming,thermal cycle parameters and welding residual stress peak and the influence of heat input and preheating on residual stress peak in single pass welding;the influence of multiple thermal cycles on thermal cycle curve and residual stress in multi-layer welding.Heat input affects welding thermal cycle and residual stress after welding.The results show that the welding current,arc voltage and welding speed affect the weld formation,the width and depth of weld pool are positively interrelated to welding current and arc voltage,and negatively interrelated to welding speed;When the heat input is in the range of 1.8KJ/cm-4.0KJcm,the peak value of equivalent residual stress is basically unchanged,but the peak values of longitudinal residual stress and axial residual stress are significantly increased;In addition,the regression analysis of residual stress with heat input and preheating temperature shows that the effect of heat input on residual stress is more significant.In multi-layer welding,the modified volume heat generation rate heat source model is more efficient than the double ellipsoid heat source model.The preheating effect of the front weld reduces the cooling rate of the follow-up weld,prolonging the high temperature residence time and cooling time,and contributing to the benign transformation of the microstructure.The peak value of the equivalent residual stress after welding is located near the welding heat affected zone.With the increase of the number of welding layers,the peak value of the residual stress decreases The stress accumulation of the inner and outer wall of the pipe is significant,and the peak value of the residual stress increases.The mechanical properties and microstructure types of girth welded joints were analyzed.The results turn out that there is no obvious defect in the ring welded joint,and the tensile test shows that the yield ratio of the material is low,the material has good ability of uniform deformation and brittle fracture resistance,and the elongation and reduction of area of the joint are large,which indicates that the material can withstand large plastic deformation without damage;with the increase of heat input,the microstructure in the heat affected zone changes obviously;the results of microhardness test show that the hardness of HAZ of X80 pipeline steel is higher than that of base metal zone,and there is no obvious softening phenomenon.