Effect of substituting SiO2 with TiO2 on viscosity and crystallisation of mould flux for casting titanium stabilised stainless steel

Abstract

During casting of titanium stabilised stainless steel, a gradual increase in TiO₂ content in the molten mould slag from absorption of TiO₂ inclusions causes changes in properties of the mould flux, such as viscosity, solidification temperature and crystallisation behaviour. To simulate this effect mould fluxes were prepared with SiO₂ being substituted with 5 and 10%TiO₂ and viscosity and crystallisation behaviour studied. Experimental results indicate that the substitution of SiO₂ with TiO₂ leads to suppression of crystallisation of cuspidine and formation of perovskite in glass quenched from mould fluxes. The crystallisation tendency is reduced by the introduction of TiO₂. The high temperature viscosity of mould fluxes shows a decrease with increasing TiO₂. At lower temperature, the viscosity of mould fluxes with 10%TiO₂ is greater than that of TiO₂ free slag, which could be attributed to precipitation of solid particles.     

Fluorine‐Free Mould Powders for Slab Casting: Crystallization Control in the CaO–SiO2–TiO2–Na2O–Al2O3 System

The main problem related to the development of fluorine‐free mould powders for slab casting is effectively controlling the heat transfer between the steel shell and mould. In commercial mould powders crystallization of cuspidine (Ca₄Si₂O₇F₂) from mould slag has a great effect on heat‐transfer control. In industrial process the crystallization rate for a fluorine‐free mould slag should be similar to the crystallization rate of cuspidine. To evaluate the crystallization rate for slags time‐temperature‐transformation (TTT) diagrams can be constructed using the Single Hot Thermocouple Technique by in situ observation. In the present work, fundamental information related to crystallization control in the CaO–SiO₂–TiO₂–Na₂O–Al₂O₃ system was obtained. It was observed that the addition of Na₂O in CaO–SiO₂–TiO₂ slags dramatically shortens the crystals' incubation times in TTT diagrams to the range of seconds. It is possible to control the crystallization kinetics in CaO–SiO₂–TiO₂ slags by changing the Na₂O content. Some observations for the crystals' morphology are reported.     

Evaluation of B2O3 as replacement for CaF2 in CaO–Al2O3 based mould flux

In order to develop low fluoride or fluoride free CaO–Al₂O₃ based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF₂ with B₂O₃ on heat transfer and crystallisation behaviour of CaO–Al₂O₃ based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF₂ promoted heat transfer of CaO–Al₂O₃ based mould flux, which was opposite to the effect of CaF₂ on heat transfer in conventional CaO–SiO₂ based mould flux. Addition of CaF₂ inhibited crystallisation of CaO–Al₂O₃ based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B₂O₃ showed similar effects to CaF₂ on heat transfer and crystallisation of CaO–Al₂O₃ based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF₂. Ca₃B₂O₆ (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al₂O₃ based mould flux compared with the primary crystalline phase Ca₂Al₃O₆F (melting temperature 1507°C) in fluoride bearing (20% CaF₂) CaO–Al₂O₃ based mould flux.     

Physicochemical Properties of CaO–SiO2–CaF2–NaF Slag system as a Mold Flux of Continuous Casting

The phase diagrams of CaO–SiO₂–CaF₂ and CaO–SiO₂–CaF₂–NaF systems were determined as a base system of mold fluxes. The commercial fluxes have the composition in which cuspidine first crystallizes. The thermodynamic stability of cuspidine was examined from the standard Gibbs energy of formation of cuspidine, which was measured, by two methods of the Galvanic cell method and the transpiration method. The effect of fluorine to silicate network was investigated. It is indicated that CaF₂ behaves as a neutral solvent for silicate slag. The crystallization in mold fluxes was measured by a high temperature XRD. Cuspidine predominantly appears because the construction of silicate glass with CaF₂ has CaF⁺ ion pair near non‐bridging oxygen. The over addition of Na₂O to mold flux prevents cuspidine from crystallizing.     

Effect of TiO2 on the crystallisation behaviour of CaF2–CaO–Al2O3–MgO slag for electroslag remelting of Ti-containing tool steel

The crystallisation characteristics of CaF₂–CaO–Al₂O₃–MgO slags with various TiO₂ contents from 0 to 9.73 mass% were studied using a single hot thermocouple technique, SEM-EDS and X-ray diffraction. The crystallisation mechanism of TiO₂-bearing slag was identified based on kinetic analysis. It was found that increasing TiO₂ from 0 to 6.43 mass% inhibited the crystallisation ability of electroslag remelting-type CaF₂–CaO–Al₂O₃–MgO slag, whereas further increasing TiO₂ content up to 9.73 mass% enhanced the slag crystallisation signally. When increasing TiO₂ content to 6.43 mass%, the crystalline phase shift from CaO to Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ at high temperatures. At lower temperatures, the crystalline phase change from polygonal Ca₁₂Al₁₄O₃₂F₂ to need-like CaTiO₃. Further increasing TiO₂ content to 9.73 mass%, the crystalline phase are Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ in the range of 1473–1613?K. The crystallisation of crystalline phase in the isothermal crystallisation is surface nucleation and controlled by interface reaction when TiO₂ content is lower than 6.43 mass% in the slag. It is bulk nucleation and diffusion-controlled one-dimensional growth in slag with 9.73 mass% TiO₂.     

Experimental investigation into radiative heat transfer characteristics for mould fluxes containing transition oxides

Abstract

Infrared transmittance of glassy and crystalline mould fluxes was measured using a Fourier transform infrared spectrometer at room temperature. Radiation heat transfer from the steel shell to the mould was calculated by a model. The results indicate that transition metal oxides MnO, FeO and TiO₂ have a marked negative effect on infrared transmittance and radiation heat flux of glassy samples. With MnO, FeO and TiO₂ added, the reductions of radiation heat flux in glassy samples are 19–25%, 34–36%, 6–29% respectively. X-ray diffraction results indicated that the crystalline phase in transition oxides free samples was mainly Ca₄Si₂O₇F₂. After transition oxides MnO, FeO and TiO₂ added, Mn₂SiO₄, Fe₂SiO₄, CaTiO₃, Ca₂SiO₄ and other minor phases were also precipitated in mould fluxes. On account of strong refraction and scattering, the negative effect on radiation heat flux in crystalline samples was much larger than that in the glassy ones.     

Properties investigation of CaO–Al2O3–SiO2–Li2O–B2O3–Ce2O3 mould flux with different w(CaO)/w(Al2O3) for heat-resistant steel continuous casting

The new CaO–Al₂O₃–SiO₂–Li₂O–B₂O₃–Ce₂O₃ mould flux was devised to realise smooth continuous casting of Ce-bearing heat-resistant steel. The new devised mould flux was based on calcium-aluminate system, so the w(CaO)/w(Al₂O₃) has great influence on the properties of the slag, which is similar to the basicity in the silicate system. The melting temperature, viscous properties, slag structure and crystalline phases with different w(CaO)/w(Al₂O₃) were investigated. The melting temperature of the mould flux could remain relatively steady with w(CaO)/w(Al₂O₃) in the range of 1.0–1.82. The main network former in the new slag was [AlO₄]-tetrahedron. The network formed by [AlO₄]-tetrahedron was destroyed by increasing w(CaO)/w(Al₂O₃), the viscosity decreased consequently. The mould flux show weaker crystallisation tendency with increasing w(CaO)/w(Al₂O₃). When the temperature decreased to 1100°C, the change of the fully crystallised phases with increasing w(CaO)/w(Al₂O₃) was as follows: Li₂O·Al₂O_3?+?2CaO·Al₂O₃·SiO_2?→?Li₂O·Al₂O_3?→?Li₂O·Al₂O_3?+?3CaO·Al₂O_3?+?CaCeAlO₄.     

Effect of CaO/Al2O3 ratio on viscosity and crystallisation behaviour of mould flux for high Al non-magnetic steel

In order to facilitate the development of CaO–Al₂O₃ based mould flux for casting high aluminium, non-magnetic steel, the effect of CaO/Al₂O₃ ratios from 0.6 to 3.2 on viscosity and crystallisation characteristics were investigated with the aid of a rotational viscometer, Fourier transform infrared spectroscopy, a single hot thermocouple technique and X-ray diffraction analysis. The results showed that, at temperatures above 1543?K (1270°C), the viscosity first decreased and then became stable with increase in the CaO/Al₂O₃ ratio. At temperatures below 1543?K (1270°C), the viscosity again first decreased but then increased, with the CaO/Al₂O₃ ratio. This viscosity behaviour can be attributed to changes in the network structure characteristics and the precipitation of solid particles within the liquid flux. Increase in the CaO/Al₂O₃ ratio also first inhibited and then enhanced crystallisation as demonstrated by the changes in initial crystallisation temperatures and incubation times. The X-ray diffraction results confirmed that, at both low and high CaO/Al₂O₃ ratios, the dominant precipitates were compounds with high melting points. On the other hand, with CaO/Al₂O₃ ratios in the midrange, the dominant precipitates were compounds with relatively low melting temperatures. It is concluded that mould flux with a CaO/Al₂O₃ ratio in the range 1.1–1.6 is the most appropriate for casting high aluminium, non-magnetic steels.     

Crystallization Characteristics of CaO-Al2O3-Based Mold Flux and Their Effects on In-Mold Performance during High-Aluminum TRIP Steels Continuous Casting

Crystallization behaviors of the newly developed lime-alumina-based mold fluxes for high-aluminum transformation induced plasticity (TRIP) steels casting were experimentally studied, and compared with those of lime-silica-based mold fluxes. The effects of mold flux crystallization characteristics on heat transfer and lubrication performance in casting high-Al TRIP steels were also evaluated. The results show that the crystallization temperatures of lime-alumina-based mold fluxes are much lower than those of lime-silica-based mold fluxes. Increasing B₂O₃ addition suppresses the crystallization of lime-alumina-based mold fluxes, while Na₂O exhibits an opposite effect. In continuous cooling of lime-alumina-based mold fluxes with high B₂O₃ contents and a CaO/Al₂O₃ ratio of 3.3, faceted cuspidine precipitates first, followed by needle-like CaO·B₂O₃ or 9CaO·3B₂O₃·CaF₂. In lime-alumina-based mold flux with low B₂O₃ content (5.4 mass pct) and a CaO/Al₂O₃ ratio of 1.2, the formation of fine CaF₂ takes place first, followed by blocky interconnected CaO·2Al₂O₃ as the dominant crystalline phase, and rod-like 2CaO·B₂O₃ precipitates at lower temperature during continuous cooling of the mold flux. In B₂O₃-free mold flux, blocky interconnected 3CaO·Al₂O₃ precipitates after CaF₂ and 3CaO·2SiO₂ formation, and takes up almost the whole crystalline fraction. The casting trials show that the mold heat transfer rate significantly decreases near the meniscus during the continuous casting using lime-alumina-mold fluxes with higher crystallinity, which brings a great reduction of surface depressions on cast slabs. However, excessive crystallinity of mold flux causes poor lubrication between mold and solidifying steel shell, which induces various defects such as drag marks on cast slab. Among the studied mold fluxes, lime-alumina-based mold fluxes with higher B₂O₃ contents and a CaO/Al₂O₃ ratio of 3.3 show comparatively improved performance.     

Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂?=?1.1–1.4, 6–12?mass% MgO and 10–16?mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.     

Analysis of basic network structure of continuous casting mould powder in electromagnetic field

ABSTRACT

In the continuous casting process, the mould powder plays the role of insulator and heat insulator in the crystallizer, prevents molten steel from oxidizing, absorbs non-metallic inclusions, and controls lubrication and heat transfer between the casting billet and the mould. It is an important functional material that promotes the quality of a billet and ensures that the continuous casting process proceeds smoothly. Here in we analyse the changes in the microstructure of the protective flux from the aspect of the infrastructure of the flux slag. Additionally, using the classical molecular dynamics simulation method, the structure of the CaO–SiO₂–Al₂O₃–MgO slag system was simulated in the presence of magnetic fields of various strengths. The magnetic field was found to have the following effects on the slag structure. The participation of the basic elements Si, Al, O, etc. in bond formation is independent of magnetic field strength. The magnetic field causes changes in the peaks, coordination numbers, and peak widths of the radial distribution functions of bonds such as Si–O, Al–O, and Mg–O. The greater the magnetic field strength, the more disordered the ionic clusters are, and the greater is the decrease in slag viscosity. Although the effect of the magnetic field influences the structure of the slag, there is not much change in the way the molecules and atoms are stacked in the slag.     

Study on Properties of Alumina‐Based Mould Fluxes for High‐Al Steel Slab Casting

During the continuous casting of high‐Al steel, the dynamic reduction of silica‐based mould fluxes by the aluminium in the steel leads to changes in their composition and physical properties. The alumina‐based mould flux has been suggested as an alternative to alleviate this reduction problem. However, until now, the smooth running of high‐Al steel continuous casting has been impeded by the lack of systematic investigation of properties of this slag. In this paper, the effects of typical components on the properties of alumina‐based mould fluxes are discussed. The experimental results show that: (a) an increase in F^? can reduce the viscosity while increasing the melting and break temperatures; (b) with increasing Li₂O, the viscosity, melting temperature, and break temperature first decrease and then increase; (c) with the addition of BaO, the viscosity, melting temperature, and break temperature remain at a low level, while a further increase in BaO causes a decrease in viscosity, an increase in melting temperature, and the stabilization of the break temperature; (d) BaO is favorable to stabilize the properties of mould fluxes for the dissolution of additional Al₂O₃; (e) the crystalline phases of the mould fluxes mainly contain 12CaO · 7Al₂O₃ and 11CaO · 7Al₂O₃ · CaF₂, and 12CaO · 7Al₂O₃ has great potential as a substitute for cuspidine.     

Quality of the Seam in Welding under Flux by Means of Barium–Strontium Carbonatite

The use of barium–strontium carbonatite in the modification and refining of ferrocarbon alloys is considered. Its use in welding fluxes is proposed. That possibility is analyzed for the example of BSK-2 barium–strontium modifier (Technical Specifications TU 1717-001-75073896–2005) produced by OOO NPK Metalltekhnoprom, with the following composition: 13.0–19.0% BaO, 3.5–7.5% SrO, 17.5–25.5% CaO, 19.8–29.8% SiO₂, 0.7–1.1% MgO, 2.5–3.5% K₂O, 1.0–2.0% Na₂O, 1.5–6.5% Fe₂O₃, 0–0.4% MnO, 1.9–3.9% Al₂O₃, 0.7–1.1% TiO₂, and 16.0–20.0% CO₂. A production technology is proposed for a flux additive containing 70% barium–strontium carbonatite and 30% liquid glass. Several welding-flux compositions based on slag from silicomanganese production are tested. The flux additive is introduced in quantities of 1, 3, and 5%. The specifics of welding under the proposed welding fluxes are determined. The chemical composition of the fluxes, the slag crusts, and the metal in the weld seam are determined by X-ray spectral analysis. The weld seams are studied metallographically. It is possible in principle to use barium–strontium carbonatite as a refining additive to welding fluxes; it also provides a protective atmosphere for the welded metal. By introducing barium–strontium carbonatite, the content of nonmetallic inclusions (nondeforming silicates, point oxides, and brittle silicates) in the weld seam may be reduced, and the desulfurizing properties of the welding fluxes may be enhanced. The introduction of up to 5% barium–strontium carbonatite in welding fluxes based on silicomanganese slag ensures that the metal in the weld seam has ferrite–pearlite structure of Widmanstatten type. The grain size is slightly reduced here: from a score of 4 to 4–5.     

Thermophysical Properties of Continuous Casting Mold Flux for Advanced Steel Developments

The effect of Al₂O₃ on the crystallization and viscosity of calcium-silicate based fluxes with Na₂O and Li₂O additions used for continuous casting mold fluxes have been studied using the confocal laser scanning microscope and the rotating spindle rheometer. Al₂O₃ additions lowered the crystallization temperature of the flux and several crystalline phases for fluxes with high concentrations of SiO₂ forms depending on the cooling rate. High Al₂O₃ containing fluxes formed relatively few crystalline phases and were not highly dependent on the cooling rate. At slow cooling rates of 25 K/min for 10 and 20 wt% Al₂O₃ containing samples, SEM images revealed dendrites formed within the crystalline phases. At faster cooling rates the dendrite formation is inhibited and a spherical morphology could be observed. The substitution of SiO₂ with Al₂O₃ content modified the dominant silicate network into complex alumino-silicates. This increased the viscosity of the melt. FTIR and Raman analysis showed increased amounts of symmetric Al–O⁰ stretching with higher Al₂O₃. With higher CaO/(SiO₂ + Al₂O₃), the symmetric Al–O⁰ stretching and the Si–O–Al seems to decrease.     

Viscosity and Viscosity Estimate Titanium-Bearing Model of Fluoride-Free and Mold Fluxes

The relationship between the binary basicity (CaO/SiO₂), TiO₂, Na₂O, Li₂O, MgO, MnO, B₂O₃ and viscosity for fluoride-free and titanium-bearing mold fluxes were systematically researched. The rotating cylinder method was employed in the experiment to measure the viscosity of the slag. The results indicate that Li₂O, B₂O₃ and Na₂O play major roles in decreasing viscosity, especially Li₂O, which is the most effective flux, while MgO and MnO exert little influence on viscosity. Meanwhile, it can be concluded that with increasing TiO₂ content, the viscosity of fluoride-free and titanium-bearing mold fluxes increases at first but then falls when the amount of TiO₂ is greater than 6.0%. Based on large amounts of experimental statistics of the viscosity of fluoride-free and titanium-bearing mold fluxes, an available model in literature for predicting the mold-slag viscosity was modified. This modified model can be used to predict the viscosity of fluoride-free and titanium-bearing mold fluxes. In fact, the predicted values approximate the observed values with a ±10.6% average deviation. Compared with the classical models, the average deviation is higher and it was found that the modified model can be used to estimate the viscosity of fluoride-free and titanium-bearing mold fluxes.     

In situ studies of agglomeration between Al2O3–CaO inclusions at metal/gas,metal/slag interfaces and in slag

Abstract

Studies of inclusion behaviour at the metal/slag interface is of great importance for the steel industry in order to achieve better control of both the size and amount of the inclusions, as well as improving the steel quality and the casting process. In this work agglomeration of liquid Al₂O₃–CaO particles at both steel/argon gas and steel/slag interfaces was studied with a confocal scanning laser microscope. In addition, agglomeration of liquid Al₂O₃–CaO–SiO₂ inclusions present in the slag was investigated. The results showed that liquid inclusions more easily agglomerated to semiliquid inclusions than to liquid inclusions. Moreover, the agglomeration of liquid particles was found to be improved remarkably when the particles were present in the slag compared to when they were in the steel/slag interface.     

Molecular dynamics simulations of microstructural properties of CaO–SiO2–TiO2 fluorine-free slag systems

The microstructural properties of F-free slag, the CaO–SiO₂–TiO₂ (CST) systems, are investigated by molecular dynamics (MD) simulations. The results show that in the CST system, the average bond length of Si–O remains in 1.61?Å. The addition of TiO₂ contributes to the increase in the concentrations of 4-coordinated Si and 4-coordinated Ti. Increasing the amount of CaO decreases the proportion of bridging oxygen (BO) atoms and the degree of network connectivity (Q³ and Q⁴), suggesting the simplification of melt polymerisation. Substituting CaO with SiO₂ and maintaining a constant TiO₂ level causes the microstructure of the slag to become more complex. Both SiO₂ and TiO₂ contribute to the more complex structures of the melts. Simultaneously, Si–O–Ti linkages are more favourable than Si–O–Si or Ti–O–Ti linkages. Thus, TiO₂ is regarded as network former in terms of its structure within CST system when the content of TiO₂ excessed 28 mass%.     

Effects of oxygen atmosphere,FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

ABSTRACT

The mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO₂–MgO–Al₂O₃–Fe_tO–P₂O₅ slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO₂ (w(CaO)/w(SiO₂))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa₂SiO₄-Ca₃(PO₄)₂ (thereafter nC₂S-C₃P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO₄ phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC₂S-C₃P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeO_x content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeO_x content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.     

F-free mould powders for low carbon steel slab casting – technological parameters and industrial trials

The choice of the mould powder for slab casting is a difficult task because mould powders have many important functions during the continuous casting of steel. CaF₂ is a key ingredient in conventional mould slags since it reduces the viscosity, the liquidus temperature and the break temperature. Fluorine in mould powders is undesirable from the environmental and health points of view due to the following reasons: (i) evolves easily from slags, producing health-injurious gaseous substances, such as hydrofluoric acid; (ii) creates problems for storage and utilisation of solid waste and (iii) causes machinery corrosion. Aim of the present work is to describe the development of a new F-free mould powder for low carbon steel slab casting replacing CaF₂ with B₂O₃. Laboratory tests and industrial trials were performed considering the technological parameters viscosity, break temperature and crystallisation tendency. From laboratory tests it was concluded that important technological parameters are similar when comparing the F-bearing mould powder (reference) and the new F-free B-bearing mould powder for low carbon steel slab casting: viscosity at 1300°C, break temperature, and crystallisation tendency. It was observed during industrial trials that a significant decrease of the submerged entry nozzle erosion was observed. The results were similar when comparing the F-bearing and the F-free performance: slag pool thickness measurements, melting behaviour, Al₂O₃ absorption, mould powder consumption and slabs superficial quality.     

Reaction performances of mould slags with different SiO2 contents for 321 stainless steel

In the present study, laboratory-scale experiments and thermodynamic calculation between the mould slags and the steel were performed to investigate reaction performances of mould slags during continuous casting (CC) of 321 stainless steel. The results show that in the final Slag1 (traditional mould slag), SiO₂ decreased by 3.86?wt-% and TiO₂ increased by 4.85?wt-%, whereas the melting temperature, viscosity and crystallization rate increased noticeably. Perovskite (CaTiO₃) and TiN were precipitated during the steel-slag reaction. Compared to Slag1, both properties and constituents of Slag2 (newly developed) with low SiO₂ changed moderately, despite TiO₂ in the final Slag2 increased by 3.96?wt-%. The precipitation of TiN and the reactivity between steel and slag were evaluated by the thermodynamic method. A comprehensive enthalpy change of steel-slag reaction was estimated to elucidate the formation of frozen steel or clogging based on the experimental results and the thermodynamic calculation.