The Research On The Temperature Field And Its Influence On Microstructure Evolution In Flux Bands Constricting Arc Welding T-joint

As a new type of lightweight structural material,high-strength steel metal sandwich panels have broad application prospects in the fields of shipbuilding,rail transit,and aerospace.However,the welding manufacturing method of high-strength steel sandwich panels has always been a key factor restricting the production and application of high-strength steel sandwich panels.Flux Bands Constricting Arc Welding(hereinafter referred to as FBCA welding)method is used to weld and prepare high-strength steel sandwich plate T-shaped joints,and a well-formed T-shaped joint can be obtained,which effectively solves the problem of insufficient penetration of the laser welded core plate.However,the characteristics of heat and mass transfer under the action of the unique flux bands constricting arc are still unclear,and the evolution of the structure of high-strength steel joints under the action of the unique heat source that determines the joint quality is also lacking in research.In view of this,this paper st udies the unique heat transfer laws of FBCA welding T-joints by collecting the temperature field distribution during the welding process of the T-joint and establishing the finite element model of the temperature field during the welding process.Then,based on this,by studying the morphology and microstructure characteristics of the welded joint,the law of microstructure evolution under the unique heat source of the FBCA welded T-joint is proposed.It provides a strong theoretical support for obtaining h igh-quality FBCA welded high-strength steel sandwich plate T-joints.First,a flexible infrared thermal imaging platform was built to accurately collect the temperature field distribution characteristics of the welding process.The results show that:compared with traditional MAG welding,FBCA welding T-joint has a larger molten pool,greater temperature field fluctuations in the back of the molten pool,and more significant diffusion effect.The cooling rate of the weld is significantly lower than that of MAG welding.In the latter part of the molten pool,MAG welding and FBCA welding are related to the sub-high temperature area of the molten pool volatility,which is related to the fluctuation of the molten pool.However,due to the unique flux bands mechanism,FBCA welding has an extra low temperature zone compared to the traditional MAG welding temperature field,which is caused by the flux bands residue that has not melted in time.Change the process parameters to analyze the temperature field and find t hat:with the increase of welding heat input,the volume of the molten pool of FBCA welding T-joint increases,the temperature rise gradient at the front end becomes larger,the width of the panel temperature field increases,and the overall temperature at the rear end of the weld rises,the arc heat has a stronger heating and melting effect on the T-joint panel and core plate.The voltage 23-25V,the current 240-280A,and the speed 7.5-8mm/s can ensure that the flux sheet effectively restricts the temperat ure conduction of the T-shaped joint.Further through the combined heat source model based on the unique heat source characteristics of FBCA welding,and through ABAQUS finite element analysis,the key temperature distribution characteristic parameters suc h as the thermal cycle curve,weld cooling time t_8/5 and isotherm profile in the FBCA welding process are obtained.Compared with the experimental results,the degree of agreement is high.Through the analysis of the finite element results and the cross-sectional morphology verification of the weld,it is found that the voltage 25-27V,the current 240-260A,and the speed7-7.5mm/s can ensure the core plate penetration without welding leakage,and the joints are well formed.The difference?L between Pmax and Pmin and the ratio K between Wx and groove width d quantitatively analyze the quality of weld formation.Next,the observation and analysis of the microstructure of the T-joint were carried out,and the results showed that the uneven distribution of the structure and grains in the partial phase transition zone is the main reason for the softening of the HAZ of the T-joint.With the increase of welding heat input(increase from 640 J/mm to 866.13 J/mm),the grain size of the coarse-grained region of the T-shaped joint increased from about 16.45?m to 28.21?m,and the grain size of the fine-grained region increased from about 7.13?m to 7.92?m,the grain size of part of the phase change zone has little change.As the heat input increases,the HAZ width of the panel and core increases,and the overall hardness decreases.