In peralkaline and meta-aluminous melts, essentially all Al3+ (>95%) occupy tetrahedral coordination, whereas for peraluminous melts, complex mixtures of aluminum triclusters with 4-fold coordinated Al3+ and Al3+ in 5- and 6-fold coordination with oxygen describe the structure. Aluminum in tetrahedral coordination requires electrical charge-balance. With alkali metals (M+) in this role, the proportions are M+=Al3+. The overall structure is dominated by three-dimensionally interconnected tetrahedra to form 6-membered rings of tetrahedra. The Al/(Al+Si) of these tetrahedra are simple positive functions of the bulk melt Al/(Al+Si). When tetrahedrally-coordinated Al3+ is charge-balanced by divalent cations, the M2+ cation charge-balances 2Al3+ tetrahedrally coordinated cations. This structure is dominated by SiO4, (Si,Al)O4, and AlO4 entities.
In peraluminous melts, where there is insufficient proportion of M2+ and M2+ cations for charge-balance, aluminum exists in triclusters with Al3+ in tetrahedral coordination. In peralkaline aluminosilicate melts, there coexist discrete structural units with different degree of silicate polymerization. These units are termed Qn-species where the superscript, n, is the number of bridging oxygen in individual units. Equilibria among these units are of the type, 2Qn = Qn+1 + Qn−1. In these melts, Al3+ is distributed among these units. The Al3+ in peralkaline aluminosilicate melts strong preference Q4 units. This preference is, however, temperature-dependent as reflected in changes in the ΔH of the Qn-species reaction.
Al-killed hot rolled steels are mainly produced with calcium treatment for the purpose either to minimize nozzle clogging in continuous casting or to modify plastic MnS inclusions. There are some negative effects of calcium treatment. In order to solve the problems, the possibility was explored to applying medium basicity refining slag for the production of hot rolled steel without calcium treatment. In this study, effect of medium basicity refining slag on desulphurization and inclusions in Al-killed steel was investigated by thermodynamic calculation and laboratory experiment. Results showed that some medium basicity slags of CaO–Al2O3–SiO2–MgO system, such as basicity of 4 and Al2O3 content of 20%, had relatively high aCaO and low aAl2O3, as well as satisfactory desulphurization efficiency, which indicated that they had strong desulphurization ability. After reacted with such slags, the surrounding part of most inclusions transformed from MgO–Al2O3, which was the main type in master steel, to MgO–Al2O3–SiO2–CaO(–MnO), the shape changes from irregular to near-spherical, and a large number of inclusions go into or near the region with relatively low melting temperature. It indicated that reaction with such slags could lower melting temperature of inclusions. In addition, steel cleanliness was improved. Based on the results, medium basicity slag may be used for production of some Al-killed hot rolled steel in which calcium treatment could be cancelled.
In this work we use thermodynamic and kinetic models to predict evolution of spinel and MgO non-metallic inclusions after argon oxygen decarburization (AOD) processing of an aluminum-deoxidized stainless steel. Inclusions form during liquid steel processing and are generally detrimental to downstream processing and steel properties. Models predicting inclusion evolution pathways have typically been applied to lower alloy content carbon steels. In this work we investigated a steel composition with alloying elements such as Cr, Co, Mo, and Nb, processed in the AOD, which utilized higher stirring rates and temperatures compared to ladle refining. Calculations were made with FactSage, with effective equilibrium reaction zone (EERZ) kinetic calculations made using the macro processing feature. Results were compared to plant sample compositions and automated inclusion analysis. The high temperatures and stirring rates present in AOD processing were observed to facilitate Mg transfer to the steel and inclusions. Modeling without the Mg*O associate in FactSage more closely fit the observed data. Additional alloying elements did not significantly change slag/metal reactions or inclusion compositions in modeling, but the strong stirring led to inclusion generation processes (reoxidation or slag entrainment) that were not accounted for in the present work. The reduction stage of AOD processing was found to be vital to inclusions in this process route.
Physical model experiments as well as numerical simulations are widely carried out to estimate flow phenomena of high-temperature liquid flow because it is difficult to observe or measure the high-temperature liquid flow directly. As for the physical modelling, similitude is an essential matter that has a great influence on the representation of real flow phenomena in the prototype. A commonsense of the physical modelling had been satisfying the similitude of one or two dimensionless numbers considering dominant forces influence on the objective flow phenomena. In this paper, physical modelling conditions required for the simultaneous similitude of multiple dimensionless numbers (SMDN) has been studied to enhance the accuracy of the flow phenomena representation. As a result, a simple relationship between physical properties of fluids and scale ratio of the physical model has become clear for the simultaneous similitude of the Froude, Reynolds, Galilei, capillary, Weber, Eötvös and Morton numbers. Then, rising velocity of bubbles has been investigated obtaining a result that the relative rising time of bubbles in the physical model corresponds well with that of the prototype under the SMDN condition. This result indicates physical models that satisfy the SMDN condition precisely represent flow phenomena of gas-liquid systems influenced by four forces; inertial force, gravitational force, viscous force and surface tension force, including bubble rising behavior as well as the bulk flow phenomena.
CaO-based slag used in hot metal pretreatment and converters in steelmaking processes typically contains dispersed gas phases. This is called foaming slag, which is known to degrade the quality of slag. The rheological behavior of this slag is dependent on the dispersed part of the gas phase. This gas is generated by the chemical reaction between the hot metal and the slag. In this study, simulated foaming slag was prepared by reacting sodium hydrogen carbonate and oxalic acid in glycerol, which disperses carbon dioxide. Next, we systematically investigated the effects of the volume fraction of the dispersed gas phase and the proportion of glycerol on the viscosity and bubble diameter. According to the model used in this study, the bubbles were smaller than those in the model in which the gas was directly dispersed. The bubble size increased as the gas phase ratio and liquid viscosity increased, likely because the bubble growth is promoted by increase in the gas phase ratio and liquid phase viscosity, and the frequency with which the bubbles contact one other. The increase of the gas phase ratio at low liquid-phase viscosity and low shear rate caused an increase in both apparent viscosity and relative viscosity, which was obtained by dividing the apparent viscosity by liquid-phase viscosity. However, these increases in viscosity were not observed at a high shear rate. This is likely because the mechanism of bubble diffusion and flow is affected by the liquid-phase viscosity and shear rate. We found that the model in this study exemplified a Herschel-Bulkley fluid. In addition, we proposed an equation for measuring viscosity from the gas phase ratio.
Iron droplet that entrapped in the refining slag reduces the yield of iron, so it is necessary to accurately estimate the settling rate of iron particle in the slag. However, since slag is a solid-liquid coexisting fluid, the sedimentation rate of iron particle cannot be derived even using the Stokes’ equation based on the viscosity of the liquid phase. In this study, using silicone oil in which polyethylene particles were suspended as a slag substitute sample, the sedimentation rate of stainless steel balls was measured, and the apparent viscosity was derived with the Stokes method. The effects of the viscosity of the silicone oil, the solid phase ratio, and the diameter of the metal balls on this apparent viscosity were investigated. It was confirmed that the apparent viscosity changes depending on the diameter of the descending metal balls.
Wetting and spreading phenomena between SiO2 single crystal and CaO–SiO2 slags with difference composition; SiO2 saturated and non-saturated slags at 1600°C were investigated by using the dispensed drop technique (DDT) with a high-speed camera (1000 frames/s). The apparent contact angle and height of non-saturated slag were significantly smaller than those of saturated slag. The apparent radii of saturated and non-saturated slags were significantly different after 0.01 s. The change in the apparent volume of the slags was analyzed by using a spherical cap model. The apparent volume of the saturated slag was constant, but that of the non-saturated slag decreased because of film type spreading. After quenching, the film type spreading was verified, and a dissolution reaction occurred in the non-saturated slag, whereas no such phenomena were observed in the saturated slag. For the saturated slag, the spreading kinetics fit well with the non-reactive viscous model suggested by a previous study. However, non-saturated slag could not be applied to spreading kinetics due to the film type spreading.
The knowledge of sulfur distribution ratios between FeO-containing slag and hot metal is necessary for better understanding resulfurization in hot metal pre-treatment. To measure sulfur distribution ratios at temperature below the melting point of pure iron, copper-iron liquid alloy has been suggested as a reference metal equilibrated with slag. In the present study, the Henrian activity coefficient of sulfur in copper-iron liquid alloy was determined at 1573 K and 1673 K. The sulfur activity coefficient decreased with an increase in iron content; this result was not inconsistent with that reported by Alcock and Richardson. Negative logarithmic value for the sulfur activity coefficient indicated that the chemical affinity between iron and sulfur would be stronger than that between copper and sulfur.
The density functional theory (DFT) has been employed to investigate the relative stability of CaFe2O4 (001) surface at seven terminations and the adsorption of CO onto the six possible topmost sites of the CaFe2O4 (001) surface. The results showed the surface energies ranged from 8.16 to 23.71 eV·nm−2 at the seven terminations and the surface with the O1 atom termination was the most stable structure. For the O1-terminated CaFe2O4 (001) surface, compared to the Ca, Fe1 and Fe2 atoms, CO molecule tended to adsorb to the topmost three O atoms. The adsorption energies were −3.19, −0.82 and −0.80 eV when CO molecule adsorbed on the O1, O2 and O3 atoms, respectively. More than 0.5 electrons were transferred to CO molecule from surface on the O sites, whereas CO molecule obtained few electrons with CO molecule adsorption on others atoms. Furthermore, two new C–O singe bonds, a new C–O double bonds, a new C–O and C–Fe single bond were generated with CO adsorption on O1, O2 and O3 sites, respectively, which implied the CO2 species formation. However, the CO2 dissociation energies were 1.80, −0.33 and 0.32 eV from the O1, O2 and O3 sites, respectively. Although CO preferentially adsorbed on O1 site to form a CaCO3-like stable sturcture, the CO2 dissociation was difficult from O1 site. Moreover, since the CO adsorption and CO2 dissociation energies were negative values, CO molecule spontaneously adsorbed on O2 site and deprived oxygen bound to iron to form the CO2 molecule.
In this work, the softening and melting (S&M) behaviour and whole blast furnace (BF) performance of Newman Blend Lump (NBLL), plant sinter, and sinter-NBLL mixture were studied using S&M under load test and numerical BF modelling. Both physical and chemical interactions between sinter and lump were confirmed in the S&M process. Significant improvements were found in the S&M behaviour of the sinter-NBLL mixture because of the physical and chemical interaction. The physical interaction was examined using X-ray/Neutron Computed Tomography (CT) scanning on the samples from interrupted S&M under load tests. The void fraction in the ferrous layer of the sinter-NBLL mixture was found to be similar to the sinter and was higher than that for NBLL. The chemical interaction was investigated by analysing the Ca transfer from sinter to NBLL, which indicated that Ca transfer started around 1200°C in the S&M process. FactSage was used to assist in the interpretation of the S&M test results. It was found that the NBLL sample starts to melt at a lower temperature compared to other burdens used in the present study, which also agreed well with the CT scan results. The whole BF performance of different ferrous burdens was studied using the experimental results as inputs. The sinter-NBLL mixture behaved more like the sinter than the NBLL; compared with the sinter only burden with the same total basicity, the sinter-NBLL combination formed a more permeable CZ, had a lower total BF pressure drop, and a higher gas utilization rate.
Oxygen blast furnace technology is expected to expand the selectivity of iron burden materials owing to its superior productivity compared to present blast furnace technology. To evaluate the possibility of utilising lump ore in an oxygen blast furnace, slag formation behaviour at the lump ore and limestone interface was investigated in this study. To focus on the slag formation behaviour in the cohesive zone, where low gas permeability can be an issue for blast furnaces, the softening behaviour between pre-reduced lump ore and a CaO substrate in an inert atmosphere was measured under loading conditions using a softening simulator. Simultaneously, cross-sectional observation and EDS analysis of quenched samples at intermediate temperatures were conducted. From the results, the following conclusions were drawn.
When melt intrusion from the lump ore to the CaO substrate occurs, the lump ore penetrates into the CaO substrate with deformation of the CaO substrate, and the greater the degree of melt intrusion, the more lump ore penetrates. The intrusion behaviour of the melt into the CaO substrate is largely related to the presence or absence of Ca2SiO4 formation at the initial melt formation start temperature. At 1300°C or lower, the gangue composition at the outer part of the lump ore is the key factor. Whereas at 1300°C or higher, where all the gangue components melt, the average gangue component of the entire lump ore is the key factor.
The coke combustion rate in the iron ore sintering process is one of the most important factors affecting the quality and productivity of iron ore sintering. The purpose of this study was to investigate the combustion rate of coke in the presence of hematite to simulate the actual conditions in a sinter machine. The experimental samples were prepared by mixing coke powder with hematite powder. Experiments were carried out under an air or N2 atmospheres at 1073, 1173 and 1273 K. From the results of the reaction curves, the coke combustion rates were analyzed using an unreacted-core model with one reaction interface.
From the kinetic analysis, it was found that the reaction rate constant kc (m/s) and effective diffusion coefficient De (m2/s) of the sample were both affected by the experimental temperature. Furthermore, the De value of the sample was affected by the amount of coke. However, the kc of the sample was not affected by this.
Utilization of biomass char, which is regarded as a carbon neutral fuel, has been discussed to decrease in the carbon dioxide emission from the ironmaking processes. However, carbonization usually leads to a significant carbon loss. In this study, the direct use of uncarbonized biomass for the reduction of iron ore was attempted. First, reduction behavior of the iron ore-uncarbonized biomass composite was examined to understand the reduction mechanism at elevated temperature. Second, reduction tests using a rotary kiln type furnace were conducted to propose a new reduction process of iron ores. In this process, stainless steel balls are utilized to supply heat and pulverize carbonized biomass and reduced iron ore through collisions with balls. The effect of process parameters on the reduction behavior was examined.
Metallic iron formed in the composite of iron ore and uncarbonized biomass by heating over 800°C under inert gas atmosphere. Heating these materials in a rotary kiln type furnace over 950°C also led to metallic iron formation. Increasing in the treatment temperature and time increasd reduction degree. The results showed a possibility that the HSM (heat storage material) balls accelerate the reduction of iron ore, and the carbonization and pulverization of biomass.
With the depletion of high-grade iron ore and increase in amount of steel scrap, a new ironmaking process utilizing both low-grade iron ore and/or steel scrap is required. The blast furnace and packed bed type partial smelting reduction process (PSR) are the most prospective reactors. When steel scrap is used as an iron source, the hot metal composition should be precisely controlled, because tramp elements such as Cu, Sn, Ni, and Cr are dissolved in hot metal. An analysis model was developed to simulate the equilibrium of the slag–metal reaction at the bottom of such reactors. The effect of scrap ratio (iron mass ratio of scrap to scrap and sinter) on hot metal and molten slag composition was thermodynamically analyzed and the optimal composition of hot metal under controlled temperature and PO2 was investigated. Si and Mn were found to be significantly oxidized relative to the equilibrium state, and the S content was equal to that at equilibrium under a blast furnace condition. As the scrap ratio increased, the Si, Mn, and P contents decreased. The Si content decreased to 0.1 mass% at T = 1773 K and PO2 > 10−13 atm or at PO2 = 3.03×10−15 atm and T < 1690 K, whereas the phosphorus content decreased at 1773 K and PO2 > 10−12 atm when the scrap ratio was 0.5. PSR is expected to produce hot metal with a low impurity content by controlling the oxygen partial pressure at the bottom of the furnace.
Influence of slag viscosity and composition on the inclusion content in the steel is studied using laboratory experiments and modeling simulations. The steel samples are taken during the experimental process to record the inclusion content change. Afterwards the prepared samples are analyzed using automated scanning electron microscope and energy dispersive spectroscopy (SEM/EDS) method. A simple steel/slag reaction model is constructed based on the effective equilibrium reaction zone (EERZ) method. The inclusion content evolution process is discussed by combining the experimental and calculated results. It is found that the inclusion content evolution in the steel is determined by the inclusion generation and removal.
The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.