Study On Composition And Process Optimization Of Fluxcored Wire In Slag-covered Arc Underwater Wet Welding

In recent years,China has gradually strengthened its awareness of maritime sovereignty and intensified its efforts in the exploitation and utilization of Marine resources,and a large number of deep-sea ships and Marine equipment have been put into use.The special Marine environment puts forward higher requirements for the maintenance and guarantee of ships and Marine equipment.Compared with electrode arc welding,flux-cored wire is used in underwater welding,the combustion of powder and metal is more effective in heat,and the flux-cored wire can effectively improve the stability of droplet metal transition and arc ionization,and significantly improve the welding efficiency.It may be the best way to improve the stability and welding quality of wet welding process if the stability and coverage of liquid slag can be increased,or even cover the arc area to achieve the effect of onshore submerged arc welding.In this paper,the welding process and mechanism of"slag arc"transition mode of underwater wet welding are studied.The welding process characteristics and mechanical properties of different components of flux cored wire were analyzed,the composition and technological parameters of flux cored wire were adjusted,and the stable transition of"slag arc type"was realized.Through the X-ray high-speed imaging system,the exploration experiments were carried out under different flux cored wire components.The analysis of the welding dynamic process and arc signal under different flux cored wire components determined that the relative content of Ca F₂ and Ti O₂ in the flux cored wire was 4:6,after welding,its shape is beautiful without obvious defects,the slag is Ti O₂-Al₂O₃-Ca O ternary slag system,the main substances in the slag are high melting point phase Ca Ti O₃ and Ca₄Ti₃O_10.The welding arc,droplet transition and liquid molten pool are all covered by liquid slag,which is defined as"slag arc type"transition.The stability of electric signal in the droplet transition mode of"slags arc covering type"is far better than that in other transition modes,the stable arc area accounts for 91%,the droplet transition diameter is1.58mm,and the droplet transition frequency is 15.9Hz.The relative content of Ca F₂ and Ti O₂ in the flux cored wire is 4:6,the orthogonal test was carried out,and the stable process parameters were obtained as welding voltage27V,welding speed 1.3-1.5mm/s,wire feeding speed 2.5m/min,and the transition ratio of"slag arc covering"reached more than 45%.The microstructure,mechanical properties and diffused hydrogen content of welds with different FCW components were studied.It was found that the proportion of the mixing zones of cellular and dendritic crystals was significantly lower than that of other components,while the mixing zones of cellular dendritic,dendritic and equiaxed grains were higher than that of other components.The depth-width ratio and grain diameter are small.Ni is the element with the largest proportion in the weld seam of each component in the test,and the other elements exist in the form of solid solution in Ni.The tensile strength and impact toughness of each group all reached the peak value when the relative content of Ca F₂ and Ti O₂ was 4:6.The tensile strength was mostly brittle fracture with the maximum tensile strength of 446.06MPa,and the impact was mostly shear daubs with the maximum impact toughness of116.41J/cm².When the relative content of Ca F₂ and Ti O₂ is 4:6,the minimum diffused hydrogen content in the weld is 3.08ml/100g.Through the analysis of high speed X-ray image,it is found that under the condition of satisfying the slag position and critical transition conditions,the slag arc type droplet transition begins to form,and the slag arc type droplet transition process can self-adjust and maintain a stable state.Under the influence of gravity(G),electromagnetic shrinkage force(F_c),slag force(F_T)and isoion current force(F_p),droplet transition occurs to overcome surface tension(F_s),spot pressure(F_b)and gas drag force(F_L),and the transition resistance is small.The transition period of droplet is 63ms.The droplet diameter was 1.58mm.Based on the principle of thermodynamic reaction,the metallurgical reaction of the arc coated core reaction zone,droplet reaction zone and molten pool reaction zone of the underwater wet welding slag was calculated.The Ca O-Ca Ti O₃-Al₂O₃ slag system was mainly formed in the end.