Deoxidation Equilibrium Research Articles

Deoxidation Equilibrium of Titanium in the Iron–Nickel Melts

Deoxidation Equilibrium of Titanium in the Iron–Nickel Melts

Ti Deoxidation Equilibrium in Molten Fe–Ni Alloys at Temperatures between 1823 to 1923 K

Equilibrium relation between Ti and O in molten Fe–Ni alloy has been investigated at 1873 to 1923 K. Ti oxide equilibrated with molten Fe–Ni alloy has been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). The present results have been numerically analyzed by the excess Gibbs free energy change of mixing for the Fe–Ni–Ti–O system with Redlich–Kister type polynomial. Redlich–Kister type polynomial parameters concerning Ni and Ti were determined as follows,0ΩNi–Ti = 424280−270.40T J/mol (XTi<0.003, 1823 K≤T≤1923 K),1ΩNi–Ti = −663380+313.15T J/mol (XTi<0.003, 1823 K≤T≤1923 K).

Aluminum Deoxidation Equilibrium of Molten Iron–Aluminum Alloy with Wide Aluminum Composition Range at 1 873 K

Al-0 equilibria in molten Fe-Al alloys were experimentally investigated. Molten steel with varying Al content (0.01-10 mass%) was equilibrated with a pure Al2O3(S) crucible at 1873 K in an Ar atmos ...

Formation Conditions of Mg2TiO4 and MgAl2O4 in Ti–Mg–Al Complex Deoxidation of Molten Iron

It is important to study the complex deoxidation equilibrium of molten iron in Ti–Mg–Al system from the view point of inclusion control. The equilibrium experiments between molten iron and TiOX–MgO–Al2O3 slag and the thermodynamic calculation on the complex deoxidation are conducted at 1973 K in the present study. The liquid phase region of TiOX–MgO–Al2O3 system in equilibrium with molten iron is clarified at 1973 K. The equilibrium compounds which are coexisted with the slag on the liquidus curve in the system are identified to be Mg2TiO4 and MgAl2O4. The equilibrium relation between the deoxidation products (Mg2TiO4 or MgAl2O4) and the composition of solute elements in steel is investigated, and the conditions that Mg2TiO4 forms instead of MgAl2O4 nor Al2O3 are examined in the complex deoxidation of Ti–Mg–Al system. When the aluminum content of molten iron is under 4 mass ppm, Mg2TiO4 forms over the wide concentration range. The concentration range of MgAl2O4 formation widens as the aluminum content of molten iron increases. It is necessary to increase Mg content and to decrease Al content in order to form Mg2TiO4 in the Ti–Mg–Al complex deoxidation of molten iron in the range Ti 0.01 mass% to form Mg2TiO4.

Ti Deoxidation Equilibrium in Molten Fe–Cr and Fe–Cr–Ni Alloys at Temperatures between 1823 K and 1923 K

Titanium deoxidation equilibria between Ti and O in molten Fe–Cr and Fe–Cr–Ni alloys were investigated at temperatures of 1823 to 1923 K. Titanium oxides equilibrated with molten Fe–Cr and Fe–Cr–Ni alloys have been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). Deoxidation product changes from Ti2O3 to Ti3O5 with decrease of Ti content in Fe–Cr and Fe–Cr–Ni alloys.Binary interaction parameters of Redlich–Kister type polynomial between Cr and O was assessed by using the previous experimental result in the Fe–Cr–O system. Experimental result of titanium deoxidation in molten Fe–Cr alloy has been numerically analyzed by the excess Gibbs free energy change of mixing Fe–Cr–Ti–O system with Redlich–Kister type polynomial. Validity of evaluated parameters between Cr–O (ΩCr–O) and Cr–Ti (ΩCr–Ti) was confirmed by comparison with experimental result for Fe–Cr–Ni alloy.Binary interaction parameters of Redlich–Kister type polynomial in present work were evaluated as follows,0ΩCr–O = −52870−24.10T J/mol (XO<0.0015, 1823≤T≤1923 K)1ΩCr–O = −498200+234.7T J/mol (XO<0.0015, 1823≤T≤1923 K)0ΩCr–Ti = 365700−206.3T J/mol (XTi<0.003, 1823≤T≤1923 K)1ΩCr–Ti = 432900−208.8T J/mol (XTi<0.003, 1823≤T≤1923 K)

Deoxidation Equilibrium of Vanadium in the Iron–Nickel Melts

Thermodynamic analysis of oxygen solutions in the Fe–Ni melts with vanadium has been carried out. The deoxidizing ability of vanadium decreases slightly with the nickel content up to 20% but it considerably rises with a further increase in its concentration. The oxygen solubility curves pass through a minimum, which shifts to the lower vanadium concentrations with a rise in the nickel content, i.e., from 2.32% for pure iron to 0.77% for pure nickel. The further vanadium addition causers an increase in the oxygen concentration in melt. For pure nickel or alloys with the nickel concentration higher than 60%, the deoxidizing ability of vanadium is lower in comparison with that of manganese and is close to the deoxidizing ability of chromium. This can be explained by the fact that although the bond strength of oxygen with nickel is appreciably weaker as compared to that with iron (γ°O(Fe)=0.0105; γ°O(Ni)=0.357), but the vanadium bond strength with nickel is much stronger than that with iron (γ°V(Fe)=0.1; γ°V(Ni)=0.011). The deoxidation of iron–nickel melts with vanadium was experimentally studied by the example of the Fe–40%Ni alloy.

Thermodynamics of Zirconium Deoxidation Equilibrium in Liquid Iron by EMF Measurements

Thermodynamics of Zr deoxidation equilibrium in liquid iron has been studied at 1873 K by using ZrO2–9mol%MgO and mullite (3Al2O3·2SiO2) electrolytes coupled with the quantitative alalysis of soluble Zr and insoluble Zr as ZrO2 by using a potentiostatic electronic extraction method. The soluble O content for a given soluble Zr content is lower than the previously reported values in the plot of soluble O vs. soluble Zr contents, and the oxygen activity for a given soluble Zr content is higher than the previously reported values. The free energy change of solid Zr dissolution into iron melt: Zr(s)=Zr at 1873 K is obtained as ΔG°=−153±10 kJ. The interaction coefficients for eOZr, rOZr and rOZr,O are estimated as −70±15, 901±131 and 10300±1500, respectively. However, the following interaction coefficients are represented by using a continuous function of logarithms of X, where X=[%sol.Zr]+5.7[%sol.O]+17.1[%sol.Zr]·[%sol.O]/(2[%sol.Zr]+5.7[%sol.O]):eOZr=−3.70−2.20 ln X−2.07(ln X)2+(ln X)3rOZr=dY/dX={−0.33+1.87 ln X+3.01(ln X)2}/XrOZr,O<11.4rOZr={−3.72+21.4 ln X+34.3(ln X)2}/X

Magnesium Deoxidation Equilibrium of Molten Fe–Ni Alloy Expressed by Quadratic Formalism and Redlich–Kister Type Polynomial

Magnesium deoxidation equilibrium of molten Fe–Cr–Ni alloy was determined by a chemical equilibrium method at temperature of 1873 to 1973 K. Extreme care was taken of oxygen analysis of the samples. Numerical analysis on Mg deoxidation of molten Fe–Cr–Ni alloy has been carried out by utilizing the model based on Darken's quadratic formalism and Redlich-Kister type polynomial. Magnesium deoxidation equilibrium can be expressed in wide composition region of the Fe–Cr–Ni alloy.

Aluminum Deoxidation Equilibrium of Molten Fe–Ni Alloy Coexisting with Alumina or Hercynite

Aluminum deoxidation equilibrium of molten Fe–Ni alloy was determined by chemical equilibrium method at temperature of 1873 to 1973 K. Also, critical point in molten Fe–40mass%Ni alloy that coexisted with Al2O3 and FeO·Al2O3 was determined experimentally at 1973 K. Solvent extraction method was applied to improve the analytical accuracy of the low aluminum content in molten Fe–Ni alloy. The relation between aluminum and oxygen contents in molten Fe–Ni alloy equilibrated with Al2O3 or FeO·Al2O3 was estimated in the whole alloy composition range at 1873 to 1973 K by utilizing the metallic solution model based on Darken's quadratic formalism and Redlich–Kister type polynomial.

Silicon Deoxidation Equilibrium of Molten Fe-Mo Alloy

In order to control the silicon deoxidation reaction for steel including molybdenum, it is necessary to take into account the thermodynamic affinity of molybdenum with silicon. For the calculation of the deoxidation equilibria in the alloyed steel including molybdenum, it is necessary to know the interaction parameter of molybdenum for silicon. However, it is difficult to explain the silicon deoxidation of the alloyed steel including molybdenum by previously reported thermodynamic data. Accordingly, the equilibrium for silicon distribution between Fe and Ag phases in Fe–Ag–Si–Mo system and the deoxidation equilibrium of molten Fe–Mo alloy with silicon are investigated at 1873 K. The atomic fraction interaction parameter of Mo for Si, eSi (in Fe)Mo, is determined to be 43(±13) from the equilibrium for silicon distribution between Fe and Ag phases in Fe–Ag–Si–Mo system. The experimental results on the deoxidation equilibrium of molten Fe–Mo alloy with silicon reasonably agree with the calculated ones by using eSi (in Fe)Mo=43(±13) derived in the present study. The oxygen contents after the deoxidation treatment by silicon are estimated for 8 kinds of steel. The oxygen content of ferrous alloys including molybdenum can be reasonably estimated using the interaction parameter of Mo for Si derived in the present study.

Effect of ferrosilicon addition on the composition of inclusions in 16Cr-14Ni-Si stainless steel melts

The silicon deoxidation equilibrium between the 16Cr-14Ni-1.5Mn-Si melts and the CaO-SiO2-8MgO-5CaF2 (basicity=1.8) slag at 1743 K was investigated to understand the effect of aluminum and silicon contents on the composition of inclusions. Therefore, the ferrosilicon alloys with different aluminum content were chosen based on the preceding objective. In addition, the phase stability diagram of the inclusions was computed using commercial thermodynamic software based on the Gibbs energy minimization principles. The content of MnO in the inclusions sharply decreases with increasing silicon content when the steel melts were deoxidized by the ferrosilicon alloys containing high aluminum (FeSi-H). The content of SiO2 in the inclusions slightly increases with increasing silicon content when the FeSi-L is used, while a maximum value is shown at [Si]=1.5 pct when the FeSi-H is used. The content of MgO in the inclusions increases by increasing the content of silicon, regardless of the kinds of ferrosilicon alloys. The use of the FeSi-L as a deoxidizer could suppress the formation of Al2O3 in the inclusions, while the content of Al2O3 increases with increasing silicon content when the FeSi-H is used. When the FeSi-H is used as a deoxidizer, the inclusions are the glassy type with the composition of Mn-silicates at [Si]≤1.3 pct, while the Mg(Ca)-silicates with the composition of the forsterite phase are observed in the steel composition of [Si]=3.3 pct. When the steel melts were deoxidized by the FeSi-L alloys, the inclusions are the glassy-type Mn-silicates at [Si]=0.8 pct, while the Mn-silicates containing the cristobalite phase are observed at [Si]=1.5 to 2.4 pct. In the composition of [Si]=3.3 pct, the Mg-silicates with the composition of the rhodonite phase are observed. The log(X SiO2/X MnO) of the inclusions linearly increases by increasing the log [a Si · a O / a Mn] with the slope close to unity when the FeSi-L is used as a deoxidizer, while the slope of the line is about 2 times greater than that of the expected value when FeSi-H is used. The log (X MgO/X MnO) of the inclusions linearly increases by increasing the log [a Mg/a Mn] with slopes greater than the expected value of unity.

Aluminum deoxidation equilibrium in liquid Fe-16 pct Cr alloy

For thermodynamic prediction, the deoxidation equilibrium of aluminum in liquid Fe-16 pct Cr alloy was studied by employing the electromagnetic levitation technique with a cold crucible in an Ar gas atmosphere at 1923 K. The interaction parameters were determined to be e Al(Fe) Cr =0.0001 (0.19/T, 1823 K≤T<1923 K) and r Al(Fe) O,Cr =−0.001. The calculated relationship between aluminum and oxygen contents in Fe-16 pct Cr alloy by thermodynamic data obtained in this study is in good accordance with the experimental results of the present study and other research.

Inclusion control of ferritic stainless steel by aluminum deoxidation and calcium treatment

A thermodynamic equilibrium between aluminum and oxygen and inclusion morphology in the Fe-16Cr stainless steel were investigated to understand the fundamentals of the aluminum deoxidation technology for ferritic stainless steels. Further, the effect of calcium addition on the changes in chemistry and morphology of inclusions was discussed. The measured results for the aluminum-oxygen equilibria exhibit relatively good agreement with the calculated values, indicating that an introduction of the first-and second-order interaction parameters, recently reported, is reasonable to numerically express the aluminum deoxidation equilibrium in a ferritic stainless steel. In the composition of dissolved aluminum content greater than about 60 ppm, pure alumina particles were observed, while the alumino-manganese silicates containing Cr2O3 appeared at less than 20 mass ppm of dissolved aluminum. The formation of calcium aluminate inclusions after Ca treatment can be discussed based on the thermodynamic equilibria among calcium, aluminum, and oxygen in the steel melt. In the composition of steel melt with relatively high content of calcium and low aluminum, the log (\(X_{CaO} /X_{Al_2 O_3 } \)) of inclusions linearly increases by increasing the log [aCa/aAl2·aO2] with the slope close to unity. However, the slope of the line is significantly lower than the expected value in the composition of steel melt with relatively low calcium and high aluminum contents.

Complex Deoxidation Equilibria of Molten Iron by Aluminum and Calcium

The influence of oxygen potential in molten steel on the steelmaking reactions, such as desulfurization and denitrogenization by fluxes, is very significant, and it is important to control oxygen content of the molten steel. The use of the strong deoxidizing agents, such as Al and Ca, is effective for decreasing oxygen content of steel, and several researches on the complex deoxidation have been carried out. However, the experimental data do not necessarily accord with the thermodynamically calculated ones, because the reliable thermodynamic data on Ca deoxidation of molten iron are unavailable. In the present study, the complex deoxidation equilibria of molten iron by Al and Ca have been examined at 1873 K. The oxygen activity in molten iron deoxidized by Al and Ca has been measured by an electro motive force (EMF) method at 1873 K. The Al-Ca complex deoxidation equilibria are presented, and the validity is confirmed from the present experimental results and the previous ones in the literature on the complex deoxidation by Al and Ca. The Al-Ca deoxidation equilibria presented in the present study can represent the relationship of Fe-Al-Ca-O system more properly than the previously reported ones.

Deoxidation Equilibrium of Chromium in Liquid Iron-Nickel Alloys

Thermodynamic analysis of oxygen solutions in iron-nickel melts with chromium has been carried out. Since the bond strength of oxygen with such a melt becomes weaker with an increase in the nickel concentration (γ°O(Fe)=0.0105; γ°O(Ni)=0.357), the deoxidation power of the chromium in liquid nickel is higher than that in iron melt.The deoxidation power of chromium remains almost constant when the nickel concentration in melt increases to 20% but it rises sharply with a further increase in its content. Oxygen solubility curves pass through a minimum, which shifts to lower chromium contents in a range of from -7% Cr (pure iron) to -1.7% Cr (pure nickel) when the nickel concentration rises. Minimum oxygen concentrations in nickel are lower almost by an order of magnitude as compared to iron. Subsequent chromium additions cause an increase in the oxygen concentration in melt; in this case, the higher the nickel content, the sharper the rise in the oxygen concentration after the minimum when chromium is added. Deoxidation of iron-nickel melts with chromium was experimentally studied for the Fe-20%Ni, Fe-40%Ni and Fe-60%Ni alloys. Experimental and calculated results are in good agreement.

Deoxidation Equilibrium of Aluminum and Silicon in the Liquid Iron-Nickel Alloys

Thermodynamic analysis and experiments showed the deoxidation ability of aluminum in the iron-nickel melts to be lower than that in pure iron and nickel. With an increase in the nickel content, the deoxidation ability of aluminum decreases to about 50% Ni and then it rises. In pure nickel, the deoxidation ability of aluminum is almost equal to that in pure iron. On one hand, this can be explained by an increase in the bond strength of aluminum with this melt when the nickel content rises (γ°Al(Fe)=0.049, γ°Al(Ni)=0.00022) and, on the other hand, by a decrease in that of oxygen (γ°O(Fe)=0.0105, γ°O(Ni)=0.357). Curves of the oxygen solubility pass through the minimum whose location is independent of the nickel content in melt. The minimum oxygen concentrations are reached at ∼0.2% Al; the further additions of aluminum result in a rise in the oxygen concentration. Experimental and calculated results are in good agreement.Complex deoxidation of Fe-40%Ni with aluminum and silicon has been experimentally studied. The formation of solutions and chemical compounds between oxides of these elements promotes the participation of silicon in the deoxidation. The lower oxygen concentrations are reached after the combined deoxidation in comparison with the aluminum deoxidation. However, when the aluminum content rises in the melt at the same silicon concentration, this difference decreases; at a certain aluminum concentration, its deoxidation power becomes equal to that of complex action of aluminum and silicon. This occurs due to an increase in the content of aluminum oxide in slag. When the slag is saturated with aluminum oxide (aAl2O3=1), silicon does not take part in the deoxidation.

Numerical Analysis on Si Deoxidation of Molten Fe, Ni, Fe-Ni, Fe-Cr, Fe-Cr-Ni, Ni-Cu and Ni-Co Alloys by Quadratic Formalism

Numerical analysis on Si deoxidation of molten Fe, Ni, Fe-Ni, Fe-Cr, Fe-Cr-Ni, Ni-Cu and Ni-Co alloys have been carried out. The excess Gibbs free energy change of mixing has described with Redlich-Kister type polynomial using the relation derived from Darken's quadratic formalism. Excellent agreement between present work and experimental results was found for equilibrium Si and O contents in molten Fe, Ni, Fe-Ni, Fe-Cr, Fe-Cr-Ni, Ni-Cu and Ni-Co alloys. Si deoxidation equilibrium of not only one component metal but also alloys can be analyzed numerically using the formula determined in the present work. Also, interaction parameters of Redlich-Kister type polynomial can be easily converted into interaction coefficients with Taylor's series, which are widely used in steelmaking processes.

Numerical Analysis on Si Deoxidation of Molten Fe-Ni and Ni-Co Alloys by Quadratic Formalism

Relation between the activity coefficient expressed by Darken's quadratic formalism and the excess Gibbs energy change of mixing described with Redlich-Kister type polynomial was discussed on Si deoxidation of Fe-Ni and Ni-Co alloys. The activity coefficients of Si and O in metal expressed by quadratic formalism have been converted into formula using interaction parameters Ω i - j under the condition where concentration of Si and O are dilute. Numerical analysis on Si deoxidation of molten Fe-Ni and Ni-Co alloy has been carried out. It has been found to be outstanding in the agreement of equilibrium Si and O contents in molten Fe-Ni and Ni-Co alloy analyzed in the present work with the experimental results. The deoxidation equilibrium of not only one component metal but also alloy can be analyzed numerically using the formula determined in the present work.

Gibbs Free Energy and Conditions of Spinel (MgO‐Al2O3) Formation in Liquid Steel

The formation conditions of spinel non‐metallic inclusion during deoxidation with aluminum in secondary refining furnace with MgO lining were discussed in the present work. The thermodynamic data of deoxidation equilibrium with magnesium, calcium and aluminum in liquid iron were determined by the authors. The activities of oxygen and dissolved deoxidizer were evaluated in the thermodynamic description by the first and second order interaction parameters including the cross product terms.

Deoxidation Equilibria among Mg, Al and O in Liquid Iron in the Presence of MgO Al2O3 Spinel.

The deoxidation equilibria among Mg, Al and O in liquid iron in the presence of MgO .A1 2 O 3 spinel was studied at 1 873 K by adding Al and Mg alloys into liquid iron in MgO and A1 2 O 3 crucibles. From the experimental results, the equilibrium constant, K Mg , for the reaction, MgO (s)=Mg+O, and the first- and second-order interaction parameters including cross-product terms between Mg and O have been determined. Using these thermodynamic parameters, the relations between a Mg vs. a o , a Mg vs. a Al in liquid iron could be well represented with respective oxide activities in MgO.A1 2 O 3 spinel. A stability diagram for MgO, MgO. A1 2 O 3 and A1 2 O 3 phases was constructed at 1 873 K as a function of dissolved Mg, Al and O contents in liquid iron to examine the condition for the formation of MgO.A1 2 O 3 spinel during the deoxidation process.