Deoxidation Equilibrium Research Articles

Thermodynamics of the Formation of Non-Metallic Inclusions during the Deoxidation of GCr15 Bearing Steel

The non-metallic inclusions in steel mainly come from the deoxidization process of molten steel. Based on the different deoxidization processes of GCr15 bearing steel produced by a domestic steel plant, the single deoxidization curves of Al, Si, and Mn and the compound deoxidization curves of Al-Si and Si-Mn under pure molten iron and GCr15 bearing steel production conditions were calculated with the FactSage 8.1 thermodynamic software. The results show that the deoxidization curves under the two conditions are quite different. At the same time, the Al-Ti deoxidation equilibrium curve under the condition of GCr15 bearing steel was calculated. It was found that when [Ti] < 0.0015% in the steel, the equilibrium deoxidation product was Al2O3, and no titanium oxide was generated. Finally, a thermodynamic calculation and analysis of the effect of rare-earth Ce content on the modification of inclusions in GCr15 bearing steel were carried out. The results showed that when T = 1873 K, the rare-earth Ce treatment of aluminum deoxidized the GCr15 bearing steel; when [Al] = 0.015%, Al2O3 inclusions increased with the increase in [Ce] content, and the evolution path was Al11O18Ce→CeAlO3→Ce2O3. When [Si] = 0.28%, [O] > 50 ppm, and CeCrO3 and [O] 0.012% appeared. CeS inclusions appeared in the steel, and the final equilibrium product was CeS + Ce2O3. When [Ce] < 0.012%, CeS was not produced in the steel, and only Ce2O3 existed.

Assessment of Si–O Equilibria and Nonmetallic Inclusion Characteristics in High Silicon Steels

Si–O deoxidation equilibria in liquid steel are not reliably known, especially in the high silicon concentration range. Herein, Si–O deoxidation equilibria in liquid steel at 1823–1873 K have been investigated for a wide range of silicon concentrations. Thermodynamic analysis was carried out using Wagner's interaction parameter formalism (WIPF) and FactSage 8.1. The first and second‐order cross‐interaction parameters estimated at 1873 K are as follows: , , . Moreover, nonmetallic inclusion characteristics were also investigated for varying silicon concentrations.

Inclusion Control of 15-5 PH High-strength Stainless Steel through Aluminum Deoxidation

15-5PH high-strength stainless steel is an important alloy used for numerous critical components. Ultra-low oxygen content and inclusion control have become urgent problems that need to be addressed for the broad application of this steel. In this study, we investigate the thermodynamic equilibrium of Al–O and inclusion morphology of 15-5PH stainless steel to understand the basic mechanism behind the results obtained after commercial production of the alloy. The deoxidation behavior of 15-5PH stainless steel depends on the dissolved Al content ([Al%]). When [Al%] <0.001%, mixed Al–Si deoxidation occurs and the deoxidation product is Al2O3–SiO2–MnO–CrOx. When [Al%] ≥0.001%, simple Al deoxidation equilibrium is dominant and the deoxidation product is MgO·Al2O3. The formation of Al2O3–SiO2–MnO–CrOx, low melting point inclusions, and a MgO·Al2O3 interface layer reduces the activity of Al2O3, which is why the calculated results of Al–O thermodynamic equilibrium are higher than the experimental results. The measured results for the Al–O equilibrium demonstrate a relatively good agreement with the calculated values. This proved that the phases formed on the crucible surfaces were in equilibrium with the Al and O contents in the molten steels after holding for 120 min.

Aluminum Deoxidation Equilibrium in Molten Fe-Co Alloys

Aluminum deoxidation equilibrium of molten Fe-Co alloy was experimentally measured using a chemical equilibrium method and numerically assessed using a sub-regular solution model based on Darken’s quadratic formalism and a Redlich-Kister type polynomial at 1873 K. It was found that the degree of oxygen content reduction by Al-deoxidation decreased with increasing cobalt concentration in the alloy, peaking at around 40 to 60 mass% Co, and then improved with further increase in cobalt concentration. The following binary interaction parameters between cobalt and aluminum were derived in this study:

Thermodynamic model and mechanism of non-alloyed hydrogen deoxidation of GCr15 bearing steel

ABSTRACT A new method of non-alloyed hydrogen deoxidation is proposed, and the hydrogen deoxidation of GCr15 is studied using thermodynamic modelling. Deoxidation by blowing hydrogen is dominated by hydrogen molecular, and the degree of deoxidation depends on , which is independent of [H]. Carbon and hydrogen will compete for deoxidation during the blowing of hydrogen. The deoxidation mode depends on the relationship between the actual and the critical . The system pressure has a great influence on the carbon / hydrogen deoxidation equilibrium. Under vacuum conditions, carbon has a stronger deoxidation ability than hydrogen. Finally, a new process for hydrogen deoxidation was proposed. In the later stage of converter smelting, hydrogen was blown to reduce the excess oxygen → tapping, and hydrogen was blown to alternate deoxidation of carbon and hydrogen → sufficient carbon powder was added into the ladle → RH treatment, and hydrogen was stopped to blown, and carbon deoxidation occurred.

Aluminum Deoxidation Equilibrium in Molten Fe–Co Alloys

Aluminum Deoxidation Equilibrium in Molten Fe–Co Alloys

Experimental Measurements and Numerical Analysis of Al Deoxidation Equilibrium of Molten Fe–Cr–Ni Alloy

Experimental Measurements and Numerical Analysis of Al Deoxidation Equilibrium of Molten Fe–Cr–Ni Alloy

Experimental Measurements and Numerical Analysis of Al Deoxidation Equilibrium of Molten Fe–Cr–Ni Alloy

Experimental Measurements and Numerical Analysis of Al Deoxidation Equilibrium of Molten Fe–Cr–Ni Alloy

Three-dimensional stability diagram of Al–Mg–O inclusions in molten steel

Stability diagrams are of great importance for investigating deoxidation equilibrium and controlling inclusions in molten steel. Combined with programming for calculation and drawing, the three-dimensional stability diagrams of MgO, MgO·Al2O3, and Al2O3 in the Fe–Al–Mg–O system were successfully drawn, which can visually explain the meaning of the iso-oxygen contours and the borderlines among different phases. They also offer straight evidence that the borderline method is imperfect. The three-dimensional stability diagrams can visually show more vital details that cannot be illustrated by the iso-oxygen contours. The most significant advantage of three-dimensional stability diagrams is not only judging the most stable phase in the specific component area but also visually showing the transformation trend among the phases from a three-dimensional perspective, especially when the equilibrium surfaces of these phases are relatively close. Besides, an interesting transformation of inclusions in the Fe–Al–Mg–O system was found. When the magnesium content is higher than 0.0065% and the aluminum content is lower than 0.21%, the equilibrium products of aluminum-magnesium composite deoxidation may be transformed from MgO to MgO·Al2O3 and Al2O3 in turn, which can be directly observed from the three-dimensional stability diagram based on the calculations.

Kinetics on Formation, Growth and Removal of Alumina Inclusions in Molten Steel

A series of Al deoxidation mechanisms from the nucleation and growth of Al2O3 nuclei immediately after the addition of Al to the growth, agglomeration, and removal of Al2O3 inclusions after the deoxidation equilibrium has been analyzed in light of the kinetics taking into consideration the influences of the interfacial properties on the basis of Al deoxidation experiments of molten steel. The nucleation number density of Al2O3 is (0.72 to 1.62) × 1014 m−3 and increases as the degree of supersaturation increases and the interfacial tension between the nuclei and molten steel decreases. These tendencies can be explained by the homogeneous nucleation theory, and the average interfacial tension, frequency factor, nucleation time, and average nucleation rate are respectively estimated to be 1.43 N·m−1, 4.27 × 1035 m−3·s−1, 0.01 s, and 1.96 × 1016 m−3·s−1 for the nucleation of Al2O3. Al2O3 nuclei rapidly grow to Al2O3 single inclusions having diameters of 2.0 to 2.6 µm through diffusion growth of supersaturated O in molten steel within 2.2 to 3.7 s after the addition of Al, and the molten steel reaches the deoxidation equilibrium. In the subsequent deoxidation equilibrium, the growth rate of Al2O3 single inclusions increases as the O concentration in molten steel increases, and their growth mechanism can be explained by Ostwald ripening. Meanwhile, Al2O3 cluster inclusions grow with the increase in the agglomeration force while agglomerating not only with single inclusions dispersed in molten steel but also with other cluster inclusions existing in the floating paths.

Deoxidation Equilibrium of Silicon in the Nickel-Cobalt Melts

The oxygen solutions in the Ni-Co melts containing silicon have been thermodynamically analyzed. The activity coefficients at infinite dilution and the interaction parameters in the Ni-Co alloys at 1873 K are calculated. The oxygen solubility depending on the silicon content in the studied alloys are obtained. Silicon is characterized by the high affinity to oxygen in these alloys. The deoxidation ability of silicon decreases slightly with an increase in the cobalt content in melt. In the Ni-Co alloys with more than 20% of cobalt, at a silicon concentration of less than 0.5%, the deoxidation ability of silicon is virtually unchangeable.

Al Deoxidation Equilibrium of Fe-10-30 mass%Mn Melt at 1873 K

Efficient and sophisticated refining process for highly alloyed steel is required in order to meet the highest-priority demand for physical and chemical properties of such steel products. In the present study, Al deoxidation equilibrium of the molten Fe-Mn system for which the demand has been continuously increasing nowadays was measured in the Mn composition range from 10 to 30 mass% at 1873 K. Equilibrated oxide phase varied depending on Al concentration; MnAl2O4 or Al2O3 was equilibrated at relatively low or high concentration range, respectively. The interaction parameter between Al and O, and equilibrium constant of Al2O3 dissolution reaction estimated from results of Al2O3-equilibrated experiments did not show the significant Mn concentration dependence of the Fe-Mn melt.

Aluminum Deoxidation Equilibrium of Fe-Ni Alloy at 1773 K and 1873 K

The aluminum deoxidation equilibrium in molten Fe-36 mass pct Ni and Fe-46 mass pct Ni alloys was experimentally determined at 1773 K and 1873 K to obtain the thermodynamic parameters around the liquidus temperature, which is required to predict the deoxidation reaction for the ingot-casting process. Automatic SEM-EDS inclusion analysis was performed to estimate the undissolved oxygen content. Thermodynamic analysis on Al deoxidation was carried out using Miki and Hino’s formula, which is based on Darken’s quadratic formalism and the Redlich–Kister polynomial. From the composition dependence of the apparent equilibrium constant in Fe-Ni alloy, the necessity of the third-order interaction parameter of Ni-Al was found. Then, the interaction parameters of Fe-Al, Al-O and Ni-Al were evaluated.

A two-step mechanism in nucleation of solid silica from Fe-O-Si melt

In order to control the structure and size distribution of silica inclusions in high purity steel, it is necessary to understand the nucleation mechanism of solid silica in molten steel. In high temperature reactions, crystallization begins with nucleation, which plays a crucial role in determining the structure and size of solid products. Nucleation originates in the formation of product intermediates. The structure and thermodynamic properties of silica clusters as the intermediate of solid silica products during nucleation were calculated by density functional theory. Comparison of thermodynamic properties of silica clusters and silicon deoxidation equilibrium experiment in liquid iron results shows the silica clusters with most of the dissolved silicon and oxygen in equilibrium; the molten iron silicon deoxidation reaction ([Si] [Formula: see text] [O] [Formula: see text] cannot reach thermodynamic equilibrium state, and some deoxidation products could only exist in the form of silica clusters but not the solid silica. Therefore, the nucleation process of solid silica in Fe-O-Si melt can be considered as a two-step process with silica clusters as intermediates. Finally, there are two paths of solid silica inclusion formation: one is that in the molten iron, the dissolved silicon reacts with the dissolved oxygen to form silica clusters, and clusters further nucleate and grow up; the second one is that silica clusters directly crystallized during the cooling process of the melt.

Deoxidation of Molten Steel by Aluminum

The deoxidation equilibrium of liquid steel was investigated from a new perspective. Dissolved associate MmOn was used to describe the interaction between dissolved M and dissolved oxygen instead of the interaction parameter of Wagner. The concentration of unassociated oxygen could be considered as the activity of oxygen. Or, the percentage of unassociated oxygen in the total dissolved oxygen was the activity coefficient of oxygen. When the content of deoxidizer was low, the dissolved oxygen was mainly composed of the unassociated oxygen, while more and more MxO formed with gradually increasing M content. The present model gave a good description to the aluminum deoxidation equilibrium after considering AlO and Al2O. Furthermore, the higher the content of Al was, the higher the content of Al2O relative to the content of AlO would be.

Thermodynamic Analysis on the Minimum of Oxygen Content in the Deoxidation Equilibrium Curve in Liquid Iron

AbstractThe minimum of oxygen content in the deoxidation equilibrium in liquid iron was thermodynamically analyzed in the present paper. Two criteria were developed to determine the existence of the minimum. The first criterion was $$0 \le x\gamma _{\rm{M}}^{\rm{M}} + y\gamma _{\rm{O}}^{\rm{M}} \le \min ({x \mathord{\left/{\vphantom {x {4.606[\% {\rm{M}}]_{{\rm{ex}}}^2}}} \right.\kern-\nulldelimiterspace} {4.606[\% {\rm{M}}]_{{\rm{ex}}}^2}},{{{{(xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}})}^2}} \mathord{\left/{\vphantom {{{{(xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}})}^2}} {3.474x}}} \right.\kern-\nulldelimiterspace} {3.474x}})$$ with $$xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}} \lt 0$$, or $$x\gamma _{\rm{M}}^{\rm{M}} + y\gamma _{\rm{O}}^{\rm{M}}{\rm{\lt 0}}$$. And the second criterion was $$(xe_{\rm{M}}^{\rm{O}} + ye_{\rm{O}}^{\rm{O}}) + {y \mathord{\left/{\vphantom {y {2.303{{[\% {\rm{O}}]}_{{\rm{ex}}}}}}} \right.\kern-\nulldelimiterspace} {2.303{{[\% {\rm{O}}]}_{{\rm{ex}}}}}} \gt 0$$. The criteria in terms of first-order activity interaction parameters were the special case of present thermodynamic analysis with neglecting the second-order activity interaction parameters. They were not fit for the case of $$xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}} \gt 0$$, in which case the criteria in terms of second-order activity interaction parameters should be taken into account to determine the existence of the minimum. The value 0.11 of $$e_{{\rm{Si}}}^{{\rm{Si}}}$$ was smaller based on the existence of the minimum for the Fe-O-Si system. It was guaranteed that the minimum value of oxygen content on the deoxidation equilibrium curve existed at silicon content 20 mass%, when the value 0.32 of $$e_{{\rm{Si}}}^{{\rm{Si}}}$$ was chosen, and the second-order activity interaction coefficients $$\gamma _{{\rm{Si}}}^{{\rm{Si}}}$$ and $$\gamma _{\rm{O}}^{{\rm{Si}}}$$ satisfied the condition $$\gamma _{{\rm{Si}}}^{{\rm{Si}}} + 2\gamma _{\rm{O}}^{{\rm{Si}}} = - 1.54 \times {10^{- 3}}$$.

Deoxidation Equilibrium of Niobium in the Iron-Nickel Melts

The oxygen solubility in iron-nickel alloys with niobium was experimentally studied in Fe-40 pct Ni melt at 1823 K (1550 °C). It was shown that the presence of niobium decreases the oxygen solubility in this melt. The equilibrium constant of interaction of niobium with oxygen dissolved in the Fe-40 pct Ni ( $$ \log K_{{(1)({\text{Fe - }}40\% {\text{Ni}})}} = {-}4.619 $$ ), the Gibbs energy of this reaction ( $$ \Delta {\text{G}}_{{(1)({\text{Fe - }}40\% {\text{Ni}})}}^{ \circ } = 161 ,210\,{\text{J}}/{\text{mol}} $$ ), and the interaction coefficients characterizing these solutions ( $$ e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{O}} = {-}0.630 $$ ; $$ e_{{{\text{O}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = {-}0.105 $$ ; $$ e_{{{\text{Nb}}({\text{Fe - }}40\,{\text{pctNi}})}}^{\text{Nb}} = 0.010 $$ ) were determined. In the wide concentration range, the equilibrium constants and Gibbs energy of interaction of niobium and oxygen dissolved in the Fe-Ni melts and the interaction coefficients for these solutions were calculated for 1823 K (1550 °C). For this temperature, the oxygen solubility in the niobium-containing Fe-Ni melts was also determined. With an increase in the nickel concentration in the alloy the niobium affinity to oxygen rises appreciably. This appears to be associated with a decrease in the bond strength between metal and oxygen in the melt as the nickel concentration increases ( $$ \gamma_{\text{O(Fe)}}^{ \circ } = 0.0084;\;\gamma_{{{\text{O}}({\text{Ni}})}}^{ \circ } = 0.297 $$ ).

Thermodynamic Analysis on Precipitation of Nonmetallic Inclusions in Gear Steel

In order to make nonmetallic inclusions with low melting point and improve the fatigue resistance of gear steel, thermodynamic analysis on precipitation of nonmetallic inclusions CaO(MgO)-Al2O3 system was investigated in this paper. The complex deoxidation equilibria of strong deoxidizing elements such as aluminum, calcium, magnesium and so on were calculated accurately with the second order and middle term of the activity coefficient expression. Thermodynamic conditions for the precipitation of spinel inclusion (MgO•Al2O3) is sufficient as the acid-soluble aluminum content is 0.04% and magnesium content is less than 0.0005% in the tested gear steel 20CrMoH. The relationship between precipitation of spinel and calcium aluminate inclusions in gear steel and the composition of molten steel at 1873K indicates that, the compositions of inclusions before and after calcium treatment are C12A7 and C3A respectively, while the reactions in ladle reach the equilibrium state.

Equilibrium between Ti and O in Molten Fe–Ni, Fe–Cr and Fe–Cr–Ni Alloys Equilibrated with ‘Ti3O5’ Solid Solution

The Ti deoxidation equilibrium of Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys saturated with ‘Ti3O5’ and Ti2O3 phase was clarified in previous researches. Solubility of Fe, Cr and/or Ni oxides in ‘Ti3O5’ phase equilibrated with liquid Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys at 1823 K to 1923 K were measured by SEM–EDS. It was confirmed that the solubility of Fe, Cr and/or Ni oxide in ‘Ti3O5’ phase at low Ti content increase with decrease of Ti content in alloys. Titanium content that dissolution of Fe, Cr and/or Ni oxide into ‘Ti3O5’ phase becomes apparent increases with increase of Cr and/or Ni content of the alloys. The activity of Ti deoxidation product, ‘Ti3O5’ phase, equilibrated with Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys was also evaluated by Redlich-Kister type polynomial. Equilibrium between Ti and O at low Ti content of those alloys was analyzed using the activity of ‘Ti3O5’ phase.

Magnesium Deoxidation Equilibrium of Molten Fe–Cr–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.