Researches On Toughening Mechanism Of High Strength X80 Pipeline Steel In Welding Heat Affected Zone

In recent years,as the demand for oil and gas resources continues to increase,the demand for large-diameter and high-pressure-resistant pipeline steel in pipeline transportation has also increased.X80 strength grade pipeline steel is currently the most widely used pipeline steel grade at home and abroad.With the development of pipeline steel towards high-strength and high-toughness high-grade pipeline steel,the strength and toughness of the welding heat-affected zone during the welding forming and welding connection of the pipeline steel also need to be continuously improved.This study intends to take X80 pipeline steel as the research object,and use the method of combining actual welding test and welding thermal simulation to obtain the welding heat-affected zone structure under the best welding process;analyze the structure parameters of the welding heat-affected zone in different areas and use simulation simulation The technology further calculates the stress-strain curve and fracture toughness J_Ic and K_Icof X80 test steel in different areas of the welding heat shadow zone,and clarifies the strength of the best welding heat input and multiphase structure parameters of high-grade X80 test steel on the welding heat affected zone.The impact mechanism of toughness.Through the welding thermal simulation experiment,the continuous curve(SHCCT curve)of the simulated welding heat-affected zone of the high-strength X80 pipeline steel is obtained,and the optimal welding heat input is analyzed in combination with the metallographic structure;through the tensile experiment,the nanomechanical indentation test and the tensile fracture Through experiments,the multi-corresponding force-strain curve,single-corresponding force-strain curve and fracture toughness J_Ic and K_Ic of the test steel under the best welding process are obtained;through the actual welding experiment and hardness test experiment,the welding heat-affected zone is divided into In multiple regions,the organization parameters of different regions are measured separately,which provides a basis for further exploring the influence of organization parameters in different regions on the strengthening and toughening of the welding heat-affected zone;Through the cellular automata and finite element coupling model(CAFE model)in PROCAST2018.0 and the cellular automata model(CA model)in DEFORM-3D,corresponding to the simulation of welding pool and welding heat-affected zone grain nucleation,During the growth process,obtain the grain growth,grain size and grain size of the welding area under different welding heat input,and further determine the best welding heat input and structure growth.Select the V-BCC unit cell model and use the ABAQUS 6.13-1 simulation software to construct the fracture toughness model of X80 test steel to simulate the influence of the structure parameters on the tensile properties and fracture properties in different areas of the welding heat affected zone,and obtain the different welding heat effects The stress-strain curve and the fracture toughness K_Ic and J_Ic values of the X80 pipeline steel are analyzed.The influence mechanism of the strength and toughness of the X80 pipeline steel welding heat-affected zone is affected by the microstructure parameters.The relationship model between fracture toughness J_Ic and f _B(Bainite content)?R_a(Bainite grain aspect ratio)of X80 pipeline steel welding heat-affected zone was further determined.