Research On Arc Behavior And Microstructure Properties Of Deep Penetration GMAW Welding In High Strength Weathering Steel Q450NQR1

Weathering steel Q450NQR1 is a railway vehicle material specially developed to meet the the high-speed and heavy-duty application requirements of railway freight vehicles.Welding is a crucial part of material forming.Efficient and high quality welding can greatly improve the performance of railway wagons.Deep penetration is an efficient welding technique.It can effectively improve the efficiency of welding manufacturing and improve the quality of joints.At present,deep penetration GMAW has achieved good performance in actual industrial production applications,but the research on deep-melting process is still in its infancy,and optimization of welding process relies on the experience of skilled workers.This paper adopts the methods of synchronous welding arc visual sensing,welding current and voltage acquisition.The difference between deep penetration GMAW arc shape and conventional gas metal arc welding is compared and analyzed.The effects of deep penetration GMAW welding current and welding speed on arc shape and weld formation were investigated.This optimizes welding process window.Welding process 1(five-pass double-sided welding and double-sided forming),welding process 2(four-pass single-sided welding and double-sided forming),welding process 3(single-sided welding and double-sided forming)were designed with optimized welding process for Q450NQR1 steel.The steels were flat-plate butt welded,and joints microstructure observation and mechanical property test were carried out after welding.The test system was built to carry out the plate surfacing test using pulsed MAG(P-MAG)and deep penetration GMAW direct current mode(DP)and pulse current mode(P-DP)respectively.Using a high-speed camera to capture the arc shape during the welding process.Analysis of weld formation after welding.The results show that the arc shape of P-MAG is a “bell jar” shape in the peak current stage,and a “cylindrical”in the base current stage.“Cylindrical” arc shape,the electromagnetic force of arc hinders the droplet from detaching from the welding wire,resulting in spatter during the welding process,undercut and porosity appear in the welding seam forming.The arc shpe of deep penetration GMAW P-DP is a “bell jar” shape in the peak current stage,and a “cone” shape in the base current stage.Conical arc shape,the electromagnetic force of arc promotes the droplet transfer,the drop transfer is high,the weld penetration is significantly largely than that of P-MAG,and the weld is free of defects.The welding process 3 can greatly improve the welding efficiency on the premise of satisfying the quality of the joint.When the deep penetration GMAW P-DP welding current increases,the arc area shrinks,the perimeter of the arc edge shortens,the position of the arc center decreases,and the corresponding penetration depth increases.As the welding speed increases,the arc expands,the edge perimeter of becomes longers,the positon of arc is raised,and the measured weld penetration decreases.The arc shape is closely related to the weld formation.When the welding current is 315 A and the welding speed is 650mm/min,the weld arc is stable,and the weld formation is excellent.The observation results of the metallographic structure show that the metallographic structure of the three process designs has little difference,The microstructure at the top of the weld is part of pro-eutectoid ferrite and a large amount of acicular ferrite,the microstructure in the transition zone between layers is mainly fine-grained ferrite,and the coarse-grained zone in the heat-affected zone is low-carbon martensitic.The mechanical test shows that the average tensile strength of welding process 1is 632 MPa,that of process 2 is 617 MPa,that of process 3 is 620 MPa.The impact absorption energy in the weld zone is about 77 J for welding process 1,75 J for welding process 2,75 J for welding process 3.The heat-affected zone impact absorption energy,the average value of welding process 1 is about 115 J,the process 2 is about115 J,and the process 3 is about 113 J.The average hardness of the weld in the welding process 1 is 211 HV,and the heat affected zone is 237 HV;the average hardness of the weld in process 2 is 223 HV,and the heat affected zone is 243HV;the average hardness of the weld in process 3 is 223 HV,and the heat affected zone is 243 HV.It exceeds the strength and toughness of the Q450NQR1 weathering steel matrix and meets the practical requirements.Through the above research,the mechanism of deep penetration GMAW arc deep penetration welding and the influence of arc behavior on weld formation have been further understood,which provides theoretical support for improving welding process stability and joint quality of deep penetration GMAW.