Study On The Structure And Physical Properties Of CaF₂-SiO₂-MnO Fused Flux For High Heat Input Submerged Arc Welding

With the rapid development of maritime trade,the shipbuilding industry is gradually facing the large-scale development.In order to adapt the needs of large-scale development of the shipbuilding industry,it is urgent to improve the efficiency of shipbuilding.Domestic and foreign enterprises widely use high heat input welding method to improve the efficiency of welding and reduce the cost,and almost all of the flux for high heat input welding is imported from Japan,so the flux suitable for high heat input welding is in urgent need to localization.Manganese silicate flux is widely used in high heat input welding due to its excellent welding performance.However,the high oxygen supply of manganese silicate flux in submerged arc welding reduces the low-temperature impact toughness of the weldment.In this paper,CaF2 was added to the manganese silicate flux to reduce the oxygen transfer to the weld metal and improve the welding performance.The effects of CaF2 content on the microstructure and physical properties of flux were studied to obtain the relationship among the composition,structure and properties of flux.In this paper,CaF2-SiO2-MnO system fused flux was designed and the phase composition of the flxux was analyzed by XRD and SEM-EDS.The microstructure of the flux was studied by Raman spectroscopy and XPS.The influence of CaF2 content on melting temperature,high temperature density and viscosity of the flux was investigated by hemispherical method,archimedes method and rotating cylinder method;the relationship between viscosity and microstructure was analyzed.Major results and conclusions are as follows:when the content of CaF2 in CaF2-SiO2MnO system flux in the range of 0?20 wt pct,the flux was amorphous structure.When the content of CaF2 was at 30?50 wt pct,the CaF2 crystal precipitated and grew.Because of the precipitation of the crystal,the ordered crystal structure appeared in the original disordered melt structure,which would change the critical transition temperature Tbr of the flux.The F-ions in CaF2 can depolymerize Q3 structure by influencing the Si-O-Si connection structure,and the O2-ions in MnO can also depolymerize.With the increase of CaF2 content,the MnO content decreased.Therefore,after CaF2 reached saturation in the melt,it precipitated in the form of crystal,and the depolymerization of O2-ion weakened.Therefore,with the increase of CaF2 content,Q3/Q2 ratio showed a trend of decreasing first and then increasing slightly,indicating that the network structure of flux melts was decomposed into simple structural units,which was reflected in the macro that the viscosity first decreased and then increased.By fitting Arrhenius formula with the viscosity data,it was concluded that the change of activation energy characterzed the movement resistance of ionic group in meld was consist with the change trend of viscosity.With the increase of CaF2 content,the melting temperature and high temperature density of flux melt decreased gradually,which was different from the linear decrease of density theoretical calculation.The actual experiment showed that the high temperature density was related to the degree of polymerization of microstructure.