Study On Flux Of 500qE Bridge Steel Submerged Arc Welding

A new fluoride type of CaO-CaF₂-MgO-Al₂O₃-SiO₂ based slag flux is developed for submerged arc welding of Q500qE high strength steel in this paper.Use the preparation of sintered welding flux,we can through the deposited metal test and welding test analysis of the mechanical properties and microstructure.Considering the bridge steel structure under the service condition of cycle load crack and low temperature impact toughness have higher requirements,the bridge component to develop in the direction of high strength,large span and heavy load.When we design the flux formula strict control of impurity element S and P content.Considering CaO can improve the basicity of slag,enhance the ability of flux to sustain current;CaF₂ as slagging agent,diluent and contribute to hydrogen,MgO can improve the flux basicity,is also the main composition of slag;Al2O3 is main effect of slagging,which can improve the viscosity of slag and increase slag surface tension;SiO₂ as acidic oxides,can reduce the slag basicity,helps improve deslagging.After using the uniform design method,design of 12 groups of flux formula.I observed weld forming state,bite edge,porosity and viscosity of slag and other defects through the welding test and to further improve the composition.Use of the preparation of X105-3 flux,matching diameter from 4.0 mm of H65Q trials on deposited metal wire,we deposited 6 layer and 13 tao.Welding process parameter control is shown as follows:the current is 500-550A,voltage is32V,welding speed is 50 cm/min.Processing of deposited metal samples and pull rods can be measured yield strength is 576 MPa,tensile strength is 672 MPa,pull rods elongation reached 30%,and-40?low temperature impact toughness is 191 J.When we used optical microscope and scanning electron microscopy?SEM?to observe analysis obtained in weld microstructure,we found that welds are mainly distributed in a large number of uniform fine acicular ferrite and pearlite and heat affected zone in a small amount of lateral plate strip ferrite.X105-3 flux of deposited metal diffusion hydrogen content is 4.51 ml/100 g,4.67 ml/100 g,3.80 ml/100 g.Through docking 20 mm thickness of Q500qE steel plate,single V groove,groove direction from positive welding first 4 layer and 6 tao,opposite to clear the root treatment continue to welding 2 layer and 3 tao,interpass temperature control at about 120?.The parameter of welding process control are:the current is500-550A,voltage is 30-32V,welding speed is 50 cm/min.By testing pull rod mechanical properties we can find that weld transverse tensile is 653 MPa,the tensile fracture location in the base area and-40?low temperature impact toughness is 160J.Weld seam and microstructure of the distribution are full of uniform fine acicular ferrite.there is pearlitic structure in weld center mingled.because we use multilayer multipass welding,in the interface between each weld,welding thermal cycle process will limit the austenitic grain to grew up,the first layer to the next layer preheating treatment and the latter is equivalent to the previous layer tempering treatment,the mechanical properties of the weld were improved.The hardness of weld center area is234.19,which is lower than that of base metal by 300.61.The softening phenomenon is more obvious in weld area.The content of Mn in the weld is 1.327%,The higher content is beneficial to the transition of manganese element,to reduce the transition temperature of weld ductile to brittle transition temperature and the austenite to ferrite transformation,thereby inhibiting the production of high temperature ferrite,is conducive to the formation of acicular ferrite in the weld.