| Inconel 625 alloy is a non-magnetic alloy with good strength and toughness from freezing temperature to 1373 K.It has excellent fatigue strength and resistance to chloride ion stress corrosion cracking.Controlling the homogeneity of alloy composition is a key part of production.As a mainstream terminal production process for Inconel 625 alloy,electroslag remelting can achieve better control of aluminum and titanium composition and desulfurization problems by selecting a suitable slag system and smelting process.This study addresses the control of aluminum and titanium elements in the process of electroslag remelting Inconel 625 alloy and focuses on the following three directions:(1)Establishing a thermodynamic model of the action concentration through the molecular ion coexistence theory to explore the interaction mechanism between slag system components and the remelting slag system suitable for smelting Inconel 625 alloy.(2)To establish a kinetic model for desulfurization during electroslag remelting and to study the influence of slag on desulfurization of Inconel 625 alloy by electroslag remelting.(3)The smelting process is used as a validation tool to conduct laboratory smelting of nickel-based alloys under different slag systems using a fixed crystallizer electroslag furnace,and the rationality of the selected slag system and smelting process is analyzed by comparing the experimental and simulated values.Firstly,in this study,Inconel 625 alloy was taken as the research object,and the slag gold balance experiments of several slag systems were carried out in MoSi2 resistance furnace.The effects of different slag systems on the composition of aluminum and titanium in the alloy were studied by measuring the mass fraction of aluminum and titanium and the final slag composition in the experimental process.The action concentration model was established by the molecular ion coexistence theory,and the thermodynamic analysis was carried out,The relationship between the activity and activity ratio of each component in the slag system and the composition of the slag system,and the influence of slag component content on the mass fraction of equilibrium aluminum and titanium in the alloy were investigated.The design principle of slag system for electroslag remelting Inconel 625 was obtained.The results show that:the classical slag system of 60%CaF2-20%Al2O3-17%CaO-3%MgO has a serious burning loss on titanium.With the increase of TiO2 content in the slag system,the value of lg(aTiO23/aAl2O32)in the slag increases,which weakens the phenomenon of "burning titanium and increasing aluminum" until the phenomenon of "burning aluminum and increasing titanium" appears.When w(TiO2)is 3,the content of aluminum and titanium in the ingot is closer to that of the original alloy.Cao in slag can cause the oxidation of Al and Ti in varying degrees.Excessive CaO can lead to the phenomenon of "burning Ti and increasing Al".Raising the temperature can inhibit the oxidation of aluminum in the alloy,and lowering the temperature can inhibit the oxidation of titanium in the alloy.At 1842 K,the most suitable content of slag elements is w(CaF2)=50%～60%,w(Al2O3)=15%～20%,w(CaO)=14%～20%,w(MgO)=3%,w(TiO2)=2.5%～3.5%.Secondly,based on the thin film theory and permeation theory,the mass transfer processes of electrode end melting into liquid film,metal droplet dropping through the slag pool into the melt pool,metal melt pool and slag pool contact interface and slag pool and gas phase contact interface during electroslag remelting are analyzed in detail,and the oxygen conservation laws between slag and metal are established for[Al]+(Al2O3),[Ti]+(TiO2),[Mn]+(MnO),[Si]+(SiO2)for six reaction systems of desulfurization kinetic equations,which were solved by using Matlab.Finally,electroslag remelting experiments with different slag systems were carried out,and the composition of the experimental electroslag ingots was examined to obtain a graph of the variation of the ingot composition along the axial direction with melting time(ingot height),and the established desulfurization kinetic model was evaluated by comparing the experimental and model values.The results show that the desulfurization rate of the control slag system(60%CaF220%Al2O3-17%CaO-3%MgO)for the electrode remelting of Inconel 625 alloy was 27%,while the designed slag system(60%CaF2-20%Al2O3-17%CaO-3%MgO with 3%TiO2)for the electrode remelting of Inconel 625 The desulfurization rate of the alloy electrode is 22%.At the same time,the designed slag system can play a good effect on aluminum and titanium preservation,which shows the rationality of the slag system design.The kinetic model of desulfurization can well reflect the dynamic change of sulfur in the electroslag remelting Inconel 625 alloy. |
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