Optimization Of Heterogeneous Microstructure And Mechanical Properties Of Shipbuilding Steels In Electro-Gas Welding By CaF₂-SiO₂ Slag System

As an important production process in the manufacturing industry,welding could consume for more than 40%of the production time.To reduce time costs and shorten production time,high heat input welding processes such as submerged arc welding and electro-gas welding are due to their low work costs,have been widely used in various fields in recent years.However,the application of electro-gas welding China is still in a developing period that most of the matching welding materials for high-heat-input electro-gas welding are in short supply and rely on imports from developed countries such as the U.S.and Japan.It makes the application of electro-gas welding in China is expensive,meanwhile which is not conducive to large-scale and long-term production.Based on this situation,the current study is devoted to the development of a new type of high-heat-input electro-gas welding flux-cored wire,and on this basis,the influence of CaF2-SiO2 smelting flux on the welding seam when used as a slagging agent is studied.Recently,the theory of oxide metallurgy has been widely studied by many scholars all around the world.The theory believes that some oxide-type inclusions with certain sizes can promote the nucleation of acicular ferrite to improve the lowtemperature toughness of the weld.The electro-gas welding flux-cored wire is added with the binary smelting flux of the CaF2-SiO2 system.The strict control of this ratio enables the weld metal to achieve good weld formability and adapt to the welding environment with higher heat input.This paper use SiO2 mass fraction of 10%,15%,20%,30%,40%five kinds of components CaF2-SiO2 type smelting flux to design five kinds of flux-cored wires with different flux core ratios.The lattice point statistics method of optical microscope found that the width of the original austenite columnar crystals of the weld structure increased with the increase of SiO2 content in the fluxcored wire.The proportion of acicular ferrite in the secondary structure increases.The number density of inclusions in the microstructure increases and the average size decreases with the field emission scanning electron microscope,and it can promote the effective inclusions of acicular ferrite nucleation.The number of inclusions also increases significantly.Besides,the electron backscatter diffraction pattern analysis shows that the proportion of large-angle grain boundaries in the weld increases,which effectively hinders the crack propagation.The low temperature impact absorption energy of the weld deposited metal was measured by-40℃ low temperature Charpy V notch impact test,which proved that adding SiO2 to the flux-cored wire has a positive effect on improving the performance of the weld metal.