Research On Flux Design Of CaF₂-Al₂O₃-TiO₂ System For High-Input Submerged Arc Welding And Its Regulating Mechanism On Weld Metal

High heat input submerged arc welding has the characteristics of high production efficiency,good weld quality and saving materials.It is also automated,mechanized,economical,environmentally friendly,and has good working conditions.It is widely used in the shipbuilding industry,which takes a large proportion of welding time.Industry,the research and development of flux in submerged arc welding is very important in high heat input energy welding process.In the welding process,the flux not only serves to start and stabilize the arc,protect the molten pool metal from contamination during the welding process,but also adjust the compositions of the weld metal through the slag-metal reaction to improve the strength and toughness of the weld.Therefore,the development of a new type of high heat input submerged arc welding flux to improve welding efficiency and weld performance is of great significance to the development of the shipbuilding industry.Fused flux has the characteristics of uniform and stable composition,easy to preserve and not easy to deteriorate.So this experiment takes fused flux as the research object.Ti element has an affinity for oxygen,which can combine with oxygen to form fine beneficial inclusions and improve the strength and toughness of the weld.Al also has a higher affinity for oxygen element,and the binding force with oxygen element is stronger than that of Ti.The studies have shown that the change of Ti and Al elements in the weld will have a certain influence on the weld properties,so Al₂O₃ and TiO₂ are used in the composition.In order to control the oxygen potential in the weld and prevent these two oxides from transitioning to excessive oxygen in the weld,the use of CaF₂ as a solvent can reduce the melting point of Al₂O₃ and TiO₂ and ensure the feasibility of smelting while controlling the weld,control the oxygen potential in the weld and avoid the high oxygen potentialIn this study,a kind of CaF₂-Al₂O₃-TiO₂ flux was designed and tested to improve the mechanical properties of EH36 shipbuilding steel after welding under high heat input energy welding.This experiment fully studied the influence of the CaF₂-Al₂O₃-TiO₂ flux on the change of weld composition,microstructure characteristics,inclusion size distribution,and the final effect on the mechanical properties of the weld.CaF₂-Al₂O₃-TiO₂ flux has a good welding performance.The Ti element in the flux can be transferred to weld pool metal through slag-metal reaction,and can form beneficial oxide inclusions with Al element O element,which can promote the formation of AF.As the network forming body,Al₂O₃ can improve the slag removal performance of the flux.TiO₂ and Al₂O₃ can provide appropriate oxygen content for the weld,which is beneficial to the formation of inclusions.With the increase of TiO₂ in the flux,the transition of Ti showed a trend of increasing at first and then decreasing,while the oxygen element continued to increase.This is because the decrease of alkalinity inhibits the transition of Ti element.The size and density of inclusions are mainly influenced by the O element and Ti element in the weld.When the oxygen content is too high,harmful inclusions of larger size will be formed,and reduce the strength of the weld.CaF₂-Al₂O₃-TiO₂ fused flux can well control the oxygen content in the weld（200 ppm to 500 ppm）,get higher impact energy welding performance.And this experiment successfully determined that the best oxygen content in the weld should be around 295ppm,the weld with this oxygen content has a relatively moderate size and quantity of inclusion,which is beneficial to the formation of AF,improve the strength of the weld,and obtain higher impact toughness.