Deoxidation Products Research Articles

Mathematical Model for Nucleation, Ostwald Ripening and Growth of Inclusion in Molten Steel

Numerical simulation is a powerful tool to investigate inclusion behavior in the molten steel. Although many mathematical models have been developed to predict inclusion collision-growth behavior in different metallurgical reactors, the inclusion size distribution had to be obtained by experiment or assumption. Thus, a general nucleation-growth model, which involves in chemical reaction, homogeneous nucleation and growth kinetics, is developed to investigate the inclusion nucleation, Ostwald ripening, Brownian collision-growth, Stokes collision-growth and turbulent collision-growth. In order to speed up the calculation, the deoxidation products are divided into two parts. The first part only consists of embryos, and directly numerical simulation is used to solve the differential equations. The second part only consists of inclusion particles, and particle-size-grouping method is introduced to solve the related equations. Numerical results showed that the predicted inclusion size distributions are consistent with previous experimental data. With the increasing diffusion coefficient, the peak-value diameter keeps unchanged and the maximum number density decreases. With the increasing turbulent energy dissipation rate, the peak-value diameter and the maximum number density decrease under the assumption on floating-out of larger inclusions.

Area method analysis and thermodynamic behavior of nonmetallic micro-inclusions in casting slab of GCr15 bearing steel

The distribution and characteristics of nonmetallic micro-inclusions of GCr15 bearing steel were explored through metallographic area method in virtue of tracer method and electronic microscope. The results show that the micro-inclusions, of which the average value is 0.032%, are mainly the compounds formed via the adsorption/aggregation of multielement deoxidized compounds and secondarily deoxidized products on tundish liquid level. The micro-inclusions of diameters from 0 to 5 μm are 92.5% in total, which basically determines the characteristics of inclusions distribution in casting slab. The inclusions of diameters more than 10 μm only account for less than 1% in total, which have little influence on steel quality. The relationship between equilibrium compositions of the first deoxidation products and molten steel compositions was also calculated based on thermodynamic theory.

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 of NiTi Alloy Melts Using Metallic Barium

The deoxidation behavior of NiTi alloy melts with metallic barium was investigated. Metallic barium was added to the NiTi alloy melts held in lime (CaO) crucibles at 1673 K, and the concentrations of oxygen, barium and calcium in the melts were quantitatively measured. The oxygen content in a raw NiTi alloy bar was 660 ppm, and the oxygen content in the NiTi alloy melts just before barium addition was around 1100 ppm. Oxygen was introduced into the melts by the dissolution of lime during melting. The addition of barium lowered the oxygen content in the melts with the formation of deoxidation product, which might be barium oxide. The oxygen content was measured to be around 350 ppm 120 s after barium addition. The barium and calcium contents were less than 10 ppm and 12 ppm, respectively, indicating that the deoxidation product was removed from the melts in a very short period of time. These results suggest that barium is an effective deoxidation element for NiTi alloy melts. Furthermore, the interaction between oxygen and barium cannot be ignored in thermodynamic considerations of the deoxidation process.

Size Distribution of Deoxidation Products with Ti, Pr and Ti/Pr in Fe–10mass%Ni Alloy

Deoxiclation experiments using Ti, Pr and Ti/Pr have been conducted using a Fe-10mass% alloy at 1 600 degrees C. The purpose of the experiments was to study the change of particle size distribution as functions of holding time, difference between the different deoxidation procedures, and amount of deoxiclant added. The Fe-10%Ni alloy was melted in a induction furnace and Ti, Pr or Ti/Pr were added as deoxidants. Samples were taken at different times after the addition of deoxidants. Thereafter, particles from each sample were extracted using electrolytic extraction. These particles where then examined in a SEM and image analyzer. Results show that the peak height of the size distribution decreases and the modal value increases with an increasing holding time. Furthermore, that the number of particles increases with an increase of deoxidant for a given initial oxygen content and holding time. The size distribution in case of the complex deoxidation using Ti followed by Pr deoxidation was also compared with cleoxiclation using only Pr.

Interface Migration Behavior of the &amp;delta;&amp;rarr;&amp;gamma; Interface in Low Carbon High Manganese Steel Samples De-oxidized with Ti or Al

The effect of inclusions, generated during de-oxidation and solidification, of low carbon (0.07wt%) and high manganese (0.9wt%) steels, on the rates of migrations of the boundaries between delta-ferrite/gamma-austenite interfaces, during austenite formation was investigated. The presence of two types of de-oxidation products were investigated, namely Al 2 O 3 (1-3μm) in Al-killed steel samples, and Ti-AI-(Mg)-O (0.3-1 μm) in Ti-killed steel samples. The samples were prepared in a vacuum-induction furnace and a Confocal Scanning Laser Microscope was used to image in real time the interface movement on the surface of the samples. Austenite was found to precipitate at the triple-points of the delta-ferrite grain boundaries during cooling from 1 500 to 1 460 and 1 450°C and the growth appeared to be diffusion controlled. The migration rates of delta/gamma interfacial boundaries were higher in the Al-killed steel samples than in the Ti-killed steel samples and this is attributed to the finer oxide particle population in the latter. When the samples were cooled to 1 440°C and below sword-like precipitation was observed in all samples that grew at a higher rate than what was observed at higher temperatures and the growth appeared to have linear time dependence, and thus the process appears to not be governed by long range diffusion.

Mass Balance Modeling for Electric Arc Furnace and Ladle Furnace System in Steelmaking Facility in Turkey

Abstract In the electric are furnace (EAF) steel production processes, scrap steel is principally used as a raw material instead of iron ore. In the steelmaking process with EAF, scrap is first melted in the furnace and then the desired chemical composition of the steel can be obtained in a special furnace such as ladle furnace (LF). This kind of furnace process is used for the secondary refining of alloy steel. LF furnace offers strong heating fluxes and enables precise temperature control, thereby allowing for the addition of desired amounts of various alloying elements. It also provides outstanding desulfurization at high-temperature treatment by reducing molten steel fluxes and removing deoxidation products. Elemental analysis with mass balance modeling is important to know the precise amount of required alloys for the LF input with respect to scrap composition. In present study, chemical reactions with mass conservation law in EAF and LF were modeled altogether as a whole system and chemical compositions of the final steel alloy output can be obtained precisely according to different scrap compositions, alloying elements ratios, and other input amounts. Besides, it was found that the mass efficiency for iron element in the system is 95. 93%. These efficiencies are calculated for all input elements as 8. 45% for C, 30. 31% for Si, 46. 36% for Mn, 30. 64% for P, 41. 96% for S, and 69. 79% for Cr, etc. These efficiencies provide valuable ideas about the amount of the input materials that are vanished or combusted for 100 kg of each of the input materials in the EAF and LF system.

ＳＵＳ３０４ステンレス鋼中スピネル介在物生成のスラグ組成による制御

The inclusion of the spinel, MgO · Al2O3, in type 304 stainless steel slab causes defect of surface, deterioration of mechanical property and so on. Thus, it is required to reduce the spinel inclusion. In this study, inclusions in molten type 304 stainless steel at each successive reactor, which were AOD, LF and tundish, were investigated in order to control the formation of the spinel in type 304 stainless steel slab. The formation of the spinel inclusions in the slab was discussed from the viewpoint of the effect of slag composition.The Al2O3 content in inclusion increased in the course of production process from AOD to slab. Moreover, the Al2O3 content in inclusion in the slab increased with the increase of Al2O3 content in slag and %CaO/%SiO2 ratio of slag. The following formation mechanism of inclusion is proposed based on these results. The origin of inclusion is formed by incorporation between the suspended AOD slag in molten steel and the deoxidation products that are SiO2 and Al2O3. When the temperature of molten steel falls, the original inclusion works as a nucleation site, namely, Al2O3 as a secondary deoxidation product precipitates at the original inclusion. Accordingly, the Al2O3 content in the inclusion increases. Based on the formation mechanism of inclusion, the semi-empirical model was constructed. This model revealed that reduction of Al2O3 content in slag and %CaO/%SiO2 ratio of slag was effective for eliminating the formation of harmful spinel inclusion.

Electrochemical Deoxidation of Molten Steel with Application of an Oxygen Permeable Membrane

The deoxidation of molten steel has been studied by employing an electrochemical cell which utilizes a solid-oxide electrolyte. This technique enables deoxidation of liquid steels without leaving deoxidation products in the steel. Y2O3-stabilized ZrO2 (YSZ) is used as an oxygen-permeable membrane due to its reasonably high mixed-ionic and electronic conductivity and thermal stability at elevated temperature in low oxygen partial pressure (PO2). In order to investigate the rate-determining steps involved in this electrochemical deoxidation process, the oxygen-permeation experiment using a YSZ disk is performed to measure the oxygen flux as a function of PO2 and temperature. The measured oxygen flux is about one order of magnitude smaller than the estimated value from Wagner equation that describes permeation under bulk-diffusion limit. Thus, oxygen permeation is mostly controlled by surface-exchange kinetics even at high temperature (~1600°C) in reducing atmosphere. In the experiment of deoxidation of molten steel using a YSZ tube, the deoxidation rate is largely dependent on the surface-exchange kinetics as well. The deoxidation rate is much smaller than that calculated under the assumption of bulk-diffusion limit. Based on these results, the surface modification of YSZ is investigated as a way to enhance the deoxidation kinetics. Both surfaces of the membrane are coated with porous YSZ (Zr0.84Y0.16O2-δ), GDC (Ce0.8Gd0.2O2-δ) and LSC (La0.7Sr0.3CrO3-δ) during oxygen permeation experiment in the gas phase. During the deoxidation experiment in the steel melt, only the permeate side is coated with Pt, Mo-YSZ cermet and LSC. The oxygen permeation rate of YSZ drastically increased with coating. The increase also depended on the coating materials. Thus, it is shown that the oxygen permeation through the membrane is mostly controlled by the surface-exchange kinetics. Similar trend can be seen in the deoxidation experiment, confirming the surface-exchange kinetics limit.

Thermodynamics of Titanium and Oxygen Dissolved in Liquid Iron Equilibrated with Titanium Oxides

The equilibrium relation of Ti and O dissolved in liquid iron saturated with solid titanium oxides was measured in the temperature range of 1 823 to 1 923 K. Pure Ti2O3 (s) phase was identified as the equilibrium deoxidation product for iron melts containing 0.25-4.75 mass% Ti. Using Wagner's formalism, the present results were thermodynamically analyzed to determine the equilibrium constant of Ti deoxidation reaction for the formation of pure Ti2O3 (s) and the first- and second-order interaction parameters between Ti and O given as follows in the temperature range of 1 823 to 1 923 K.2Ti+3O=Ti2O3 (s) (0.25<mass% Ti<4.75)log KTi2O3=44238/T−13.0eOTi=−1642/T+0.3358, eTiO=−4 915/T+1.005rOTi=0.0385, rTiO=−0.355The equilibrium titanium oxide phase was identified as Ti3O5 (s) for iron melts containing 0.0012-0.25 mass% Ti at 1 873 K. The equilibrium constant of Ti deoxidation reaction for the formation of pure Ti3O5 (s) were estimated as follows.3Ti+5O=Ti3O5 (s) (0.0012<mass% Ti<0.25)log KTi3O5=72813/T−21.32The activity coefficient of Ti in liquid iron at infinite dilution, γ°Ti(s) was assessed as 0.011, 0.014 and 0.018 at 1 823 K, 1 873 K and 1 923 K, respectively.

Thermodynamics of surface phenomena in liquid metal at phase boundaries

The formation of wetting films of liquid alloys on nonmetallic inclusions (deoxidation products and slag) enhances the stability of suspensions formed by them and ultimately impedes the removal of inclusions (facilitates the return of inclusions to the melt). The conditions necessary for the stability of films on the surface of solids are established on the basis of the classical laws of thermodynamics. Results from empirical measurements of the tension of thin and thick films of metals are discussed, and thermodynamic equations describing the migration of nonmetallic inclusions (destabilization of their suspensions in steels) are obtained for metallurgical operations under specific conditions. Criterional equations are obtained to determine the stability of disperse metallurgical systems (suspensions) with allowance for the formation of films, the effect of disjoining pressure, and the presence of slags. Estimates are made of the stability of suspensions of nonmetallic inclusions (deoxidation products and process slags) in steels.

The Influence of Non-Metallic Inclusions Physical State on Effectiveness of the Steel Filtration Process

The work presents theoretical fundamentals of the process of refining molten steel from liquid non-metallic inclusions, using the method of filtration with ceramic filters - the thermodynamic precondition for the absorption of liquid non-metallic inclusions on the surface of a ceramic filter. The theoretical consideration has been supported by the results of laboratory tests on the filtration of steel which was previously reduced with complex deoxidants giving liquid products of deoxidization. The filtration process of steel melts reduced with complex deoxidants of type Al-Mn-Si has proved to be more efficient. The deoxidation products were identified on the filtration surface of the ceramic filters.

Inclusion and Bubble in Steel — A Review

The type, morphology and sources of inclusion in steels, including indigenous and exogenous inclusions, were discussed and reviewed. Indigenous inclusions are deoxidation products or inclusions precipitated during cooling and solidification of steel. Exogenous inclusions arise primarily from the incidental chemical (reoxidation) and mechanical interaction of liquid steel with its surroundings (slag entrainment and erosion of lining refractory). Types and causes for the nozzle clogging were also summarized. Reasons for bubble formation and bubble size distribution in steels were discussed thereafter. Finally, morphology and causes of inclusion-related defects in continuously cast steel products were reviewed, such as flange cracking in cans, slag spots and line defects on strips.

Effects of Dissolved Oxygen and Size Distribution on Particle Coarsening of Deoxidation Product

The growth mechanism for deoxidation products of MgO, ZrO2, Al2O3, CaO–Al2O3 and MnO–SiO2 in an Fe–10mass%Ni alloy has been studied under the condition of no fluid flow by considering the effects of dissolved oxygen and size distribution on Ostwald ripening. The coarsening rate of particles is largely dependent on the dissolved oxygen content. The spread of particle size distribution decreases in the order of Al2O3>ZrO2>MgO>CaO–Al2O3>MnO/SiO2 particles and that of solid Al2O3, ZrO2 and MgO particles becomes narrower with holding time. The coarsening rate is also affected by the spread of size distribution curve and this is the reason that the coarsening rate of Al2O3 particles is larger than that predicted from dissolved oxygen content.

Precipitation and Dispersion Control of MnS by Deoxidation Products of ZrO2, Al2O3, MgO and MnO–SiO2 Particles in Fe–10mass%Ni Alloy

An Fe–10 mass%Ni–1mass%Mn alloy was deoxidized with Zr, Al, Mg and Si and the effect of these deoxidation particles on MnS crystallization and/or precipitation has been studied as a function of S content with forcussing on the particle dispersion in microsegregation domain. MnS cannot be uniformly dispersed in microsegregtion domain since the crystallization and/or precipitation of MnS occur only on ZrO2 or Al2O3 particles located at the region of final solidification. MnS-containing MnO–SiO2 particles can be uniformly dispersed in microsegregation domain, if the S level is low enough for particles not to be pushed. MgS and/or (Mg, Mn)S crystallize on MgO particles in Mg deoxidation. In the case of high S level, the MgO, MgS/MgO and (Mg, Mn)S/MgO particles are pushed to the region of final solidification and then MnS crystallizes and/or precipitates on the pushed particles.

Characteristics of Particle Size Distribution of Deoxidation Products with Mg, Zr, Al, Ca, Si/Mn and Mg/Al in Fe-10mass%Ni Alloy

In the experiments of an Fe–10mass%Ni alloy deoxidized with Mg, Zr, Al, Ca, Mn/Si and Al/Mg at 1873 K, the characteristics of particle size distributions have been studied as a function of holding time, amount of deoxidant and order of deoxidant addition. The peak height in particle size distribution decreases and the modal value increases with increasing holding time. The width of the distribution curve is larger for Al2O3 particles and smaller for liquid CaO–Al2O3 and MnO–SiO2 particles. The number of particles increases with an increase of deoxidant for a given initial oxygen content and holding time. In the case of Al followed by Mg deoxidation, the particle size distribution is almost the same as that obtained by only Al. The size distribution in case of Mg followed by Al deoxidation is almost the same as that by only Mg.

Refinement of Solidification Microstructure and Austenite Grain by Fine Inclusion Particles

The effect of deoxidation products of Ce2O3, ZrO2 and MgO particles on solidification microstructure has been studied in Fe–10mass%Ni, Fe–0.20mass%C–0.02mass%P and Fe–0.50mass%C–1mass%Mn alloys. The degree of the equiaxed crystallization is explained by the lattice misfit parameter between γ (or δ)-Fe and oxide. The single-phase solidification microstructure of Fe–10mass%Ni and Fe–0.50mass%C–1mass%Mn alloys is well related to austenite grain boundaries under the inhibition of grain growth by pinning. The correspondence between solidification structure and initial austenite grain has been studied in two-phases solidification of Fe–0.15 (or 0.30)mass%C–1mass%Mn–1mass%Ni alloy. The γ-grain size decreases with decreasing the lattice misfit parameter between γ-Fe and oxide and increases with decreasing the Zener pinning force. The number of γ-grains to that of primary δ-grains per unit area in a cross section increases with decreasing the aforementioned lattice misfit parameter, indicating that more than one nucleation event per δ-grain occurs at δ-ferrite grain boundary during δ to γ transformation.

Characteristics of Particle Size Distribution in Early Stage of Deoxidation

The spread of the size distributions obtained by deoxidizing an Fe–10mass%Ni alloy with Zr, Mg, Al, Ca and Si/Mn has been discussed with particular emphasis on the particle size distribution soon after the nucleation of deoxidation product. The geometric standard deviation in size distribution was found to be related to the interfacial energy between oxide and liquid Fe, γoxide–Fe(I). The nucleation rate decreases with an increase in γoxide–Fe(I) based on the homogeneous nucleation theory. Thus, the geometric standard deviation decreases with increasing the nucleation rate in which γoxide–Fe(I) is low such as the case of MnO–SiO2 particles. The experiment in which an Fe–10mass%Ni alloy was first deoxidized with Ti followed by Mg was carried out and narrow size distribution was obtained by separating the nucleation and growth processes.

Zero Inclusion Steel and its Oxide Inclusions Characteristics

Vacuum induction melting and electron beam melting have been used to produce a steel with a composition of 4×10−6 T[O], 5×10−6 [S], 3×10−6 [N]. Examining the samples of the steel with original position analysis and SEM showed that the non‐metallic inclusions in the steel were mainly alumina particles with a size ranging from 1 to 4 microns. The morphology and composition of the inclusions extracted electrolytically from the steel were analysed using SEM and EDS. It was found that some deoxidization products and lining materials with a size ranging from 10 to 20 microns, and some flux inclusions with a size around 40 microns existed in the steel. Most of these bigger inclusions originated from raw materials. Finally this paper also proposed an effective method to remove these bigger inclusion particles from zero inclusion steel.