High temperature slags could act as not only heat carrier and catalyst but also reactants in some chemical reactions to produce syngas due to the individual components in slags. A new method is put forward to utilize the thermal energy of converter slags to generate CO gas which could improve the energy utilization efficiency. Thermodynamics of the reactions among coal, FeO–CaO–SiO2 slag and gas was studied by thermodynamic calculation under steady temperature condition or no enthalpy change condition. The effects of FeO amount in initial slag, mass%CaO/mass%SiO2 ratio of slag, and slag temperature on the behavior of the production of H2 and CO gases were clarified.
It is known that the two-equation turbulence models under-predict the turbulence mixing shear process for the compressible non-isothermal jet. In this study, a temperature corrected turbulence model on the basis of the SST k-ω model was proposed to predict the behavior of the cold supersonic oxygen jet injecting into the high-temperature environment. The results show that the corrected SST k-ω model is superior to previous corrected k-ε models when simulating the whole process of the supersonic oxygen jet flowing from a Laval nozzle into free space. Meanwhile, the calculation results of the outlet free jet at 285 K, 772 K and 1002 K are in good agreement with experimental data and empirical formulas in the literature. Furthermore, the behavior of the supersonic oxygen jet at 1873 K is predicted by the proposed model. In addition, the effects of the ambient temperature on the jet core length and the interaction between multiple jets were also studied.
Several studies have examined the reduction behavior of manganese ore at high temperature with the aim of reducing the manganese cost in the steelmaking process. However, the transformation behavior of manganese compounds at high temperatures had not yet been clarified. Therefore, in this paper, the effects of temperature and oxygen partial pressure, as well as chemical composition, on the transformation and melting behavior of manganese ore were investigated by using high temperature X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) in order to obtain fundamental information on the pre-reduction process of manganese ore. The main manganese compound in the raw manganese ore used in this study was characterized as CaMn6SiO12 by XRD at room temperature, while the main Mn compounds in the sintered manganese ore were Mn3O4 and MnO. Under a vacuum condition, raw manganese ore and sintered manganese ore were reduced to MnO above 1473 K. However, under atmospheric conditions (pressure: 760 Torr), manganese ore was reduced to Mn3O4 rather than MnO at temperatures above 1073 K. The results of high temperature XRD agreed with thermodynamic calculations. The melting temperature of the raw manganese ore evaluated by TG-DTA was lower than that of the sintered manganese ore due to the difference in the manganese oxide in each ore rather than the difference in the content of gangue components such as Al2O3, CaO, MgO and Fe2O3. The higher melting temperature of the sintered manganese ore is interpreted in terms of a higher content of MnO due to heat treatment.
A metal emulsion is formed by the passage of gas bubbles through the interface between the metal phase and the slag phase in the steelmaking process. Emulsified metal droplets have great potential to improve the chemical reaction efficiency during motion in bulk slag. Several studies have focused on the formation mechanism of metal droplets and on the influence of the physical properties of the system on this mechanism. In this study, Sn alloy and sodium tetraborate were used to simulate molten steel and slag, respectively. Gas bubbles were introduced from the bottom of a molten metal bath at various gas flow rates. Slag containing metal droplets at the center of the slag phase was sampled, and the metal droplets were extracted by the dissolution of the oxide in a solvent. The number and diameter of the droplets were measured using a digital microscope. Under the same experimental conditions, the number of metal droplets in the oxide system was smaller but their size was larger than those in a previously investigated Sn alloy/chloride system. In both the systems, the total mass of metal droplets formed by a single bubble increased with an increase in the volume of the gas bubble, and when the volume of the gas bubble was small, the total mass of droplets in the oxide system was smaller than that in the chloride system. The sedimentation rate and coefficient in the oxide system were lower than those in the chloride system.
The interaction parameter between Cu and Al in molten iron containing high levels of Al was measured using a chemical equilibrium technique. A molten Fe–Al alloy was equilibrated with a molten Ag–Cu alloy in an Al2O3 crucible at 1823 K. The activity coefficient of Cu in Fe–Al alloys was measured to be −2.33 while varying the concentration of Al in a range from 0.04–0.2 mol%. The influence of Cu on the deoxidation equilibrium of Al and O was estimated using the above interaction parameter. The results indicate that under a constant Al concentration, a contamination of several percent of Cu raises the O concentration in high Al steel.
High manganese-aluminum steel have obtained great attention because of their excellent strength, ductility and formability. However, a high manganese content can increase the solubility of nitrogen significantly and result in the formation of the AlN inclusions during the process of steelmaking. Therefore, a better understanding and control of nitrogen content and AlN inclusions in Fe–Mn–Al melts is essential for the process of steelmaking. In this work, the nitrogen solubility in Fe–Mn–Al melts ([%Mn]<20, [%Al]<2) was measured at 1873 K under the nitrogen partial pressure range of 0.1 atm to 0.4 atm. It was concluded from the experimental results that nitrogen solubility decreased with the increase of aluminum content, but increased with the increase of manganese content. Moreover, AlN inclusions were found in the samples with the aluminum content of 1.3 mass% and 1.4 mass% under the nitrogen partial pressure of 0.4 atm. It was also confirmed that the interaction parameters of thermodynamic model for Fe–Mn–Al–N system determined by Paek et al. were effective over a wide range of aluminum content and nitrogen partial pressure.
Nitrogen solubility of two typical compositions of practical Mn–Si–Fe melts were measured by the gas-liquid metal equilibration technique in the range of 1673 to 1773 K under different nitrogen partial pressures, especially high nitrogen partial pressure close to pure nitrogen gas. It was found that nitrogen solubility increased as the increase of temperature but decreased as the increase of silicon content. The nitrogen partial pressure dependence of nitrogen solubility for 68 mass%Mn-18 mass%Si-Fe and 60 mass%Mn-30 mass%Si-Fe melts follows the Sievert’s law. Relative to pure Mn melt, which doesn’t obey the Sievert’s law, the increase of silicon or iron content in Mn–Si–Fe melts could decrease the deviation degree from the Sievert’s law. Silicon nitride precipitates were formed at the surface of the 60 mass%Mn-30 mass%Si-Fe melts at 1773 K when the nitrogen partial pressure is 0.4.
Silica is a significant chemical component in the formation of SiO2–Fe2O3–CaO–Al2O3 from CaO·Fe2O3 (CF). The influence of silica on the reducibility of the CaO–Fe2O3–SiO2 system was fully examined in this study. The isothermal reduction kinetics of CF, CF2S, CF4S, and CF8S were investigated through thermogravimetric analysis at 1123, 1173, and 1223 K with 30% CO and 70% N2 gas mixtures. CF2S and CF4S presented a slight degrader in reduction degree but activated the reaction faster than CF reduction. The reduction of the samples with 8% silica was not only highly accelerated but also proceeded easily. Rate analysis revealed that CF and CF8S reduction occurs in two stages, whereas CF2S and CF4S reduction occurs in three stages, the Fe3O4–to–FeO stage overlaps with the previous Fe2O3–to–Fe3O4 stage and tends to approach the following FeO–to–Fe stage with an increase in silica content. The apparent activation energy values of CF, CF2S, CF4S and CF8S reduction are 46.89, 24.48, 44.84, and 8.71 kJ·mol−1. CO diffusion is the rate–controlling step of the entire process of CF8S reduction, whereas the rate–controlling step of CF, CF2S and CF4S reduction are performed as inner gas diffusion, inner gas diffusion and interface chemical reaction mixed control then interface chemical reaction in turns with reduction degree increasing. Sharp analysis indicated that CF and CF8S reduction was expressed by the Avrami–Erofeev equation presenting a 2D shrinking layer reaction, whereas CF2S and CF4S reduction was expressed initially by a 2D shrinking layer reaction and then by a 2D phase boundary–controlled reaction.
The degradation behaviors of coke which reacts with CO2 and H2O were explored in self-made gas-solid reacting apparatus. It was observed that the temperature loss of coke with H2O in initial and violent solution were about 37°C and 125°C lower than that with CO2 respectively. The gasification rate of coke with H2O was about 1.27–3.16 times faster than that with CO2. But the difference of gasification rate will reduce with the lower temperature. The coke strength after reaction (CSR) with H2O was lower than with CO2 at 950°C–1100°C, but higher at 1200°C. The coke’s apparent porosity and changing rate after reacting were both smaller with H2O than with CO2. It is mainly due to the reaction that occurred closer to the coke particle surface with H2O than with CO2.
The effects of particle size distribution (narrow, Gaussian, binary and flat) on high-temperature defluidization behavior of iron powder were investigated. The fluidization characteristics were studied involving minimum fluidization velocity, bubbling velocity and bed voidage. The thermo-mechanical analysis was applied to examine the sintering temperature and surface viscosity of iron powder due to surface softening. The results indicated that the effects of PSD on defluidizaton were dependent on temperature. The Gaussian distribution was favorable to fluidization and presented better fluidization quality at lower temperatures. However, at higher temperatures, the narrow distribution exhibited a higher defluidization temperature and thus a lower agglomeration tendency due to a larger apparent viscosity and lower particle stickiness. Therefore, the PSD apparently affected not only hydrodynamic behavior, but also particle adhesion of bed materials for defluidization.
Iron ore pellets degrade and generate dust during transportation and handling as well as during the iron making process. This leads to material losses and effects the process efficiency in a negative manner. In order, to reduce the generation of dust it is important to understand the influence of process parameters on the dust formation. An experimental setup was used to measure the dust generation and friction forces caused by abrasion of iron ore pellets in a closed pack bed. A varied load of 1 to 3 kg was applied on the pellet bed but at a constant air flow rate to capture the airborne dust particles. It was observed that an increase of ~67% is observed in the friction and the dust generation in the bed as the applied load increased from 1 to 3 kg. Moreover, the evaluation of the particle size distribution of the generated dust showed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. Moreover, it has been shown that in an air flow the morphology and the orientation of dust particles can influence the air velocity required to transport the particles upwards.
Improved permeability and increased gas utilization have been desired in order to achieve low coke rate operation of blast furnaces. Coke mixed charging in the ore layer is one of the effective measures for realizing these improvements. A new charging technique for mixing small coke in the ore layer at a blast furnace with a center feed type bell-less top was developed and investigated in an experiment with a 1/18.8 scale model of an actual blast furnace at JFE Steel. By the new charging technique that small coke was charged in the determined port of the upper bunker before ore was charged in the upper bunker, the discharge pattern of the mixed small coke discharged from the bell-less top was improved, and the radial distribution of the mixed small coke ratio at the furnace top after the mixed materials were charged in the blast furnace was also improved. The new charging technique was applied to an actual blast furnace at JFE Steel, and improvement of gas permeability and a decrease in the coke rate were confirmed.
The aim of this study was to elucidate the speciation of PM2.5 and proportion of each typical speciation via calculation of chemical mass balance. The results from elemental and morphological analyses showed that PM2.5 consisted of diverse components mainly including O, Fe, Ca, Al, Si, and trace elements K, Na, Pb, S, and Cl. These components mainly existed in spherical, cubic, polyhedral, flake-like and bulk-like particles. Through examining the chemical composition and distribution property of main components in typical particles, Fe, Ca and O were determined to present in the speciation of Fe2O3–CaO from melting process, while Al, Si and O existed in the speciation of xAl2O3-ySiO2 from fuel fly ash. K, Na, Pb and Cl could exist in the speciation of KCl, NaCl and PbCl2 respectively from chlorination reactions. Moreover, Ca, K, Pb, O and S could form sulfates of CaSO4, K2SO4 and PbSO4 respectively. Calculation of O, S and Cl equilibrium in PM2.5 indicated that Fe2O3–CaO accounted for about 30.63%, xAl2O3-ySiO2 accounted for about 7.02%, K(Pb/Na)Clx accounted for about 41.29%–49.77%, and K2(Ca/Pb)SO4 accounted for about 21.05%–12.57%.
(a) Molar ratio of calculated value to practical one; (b) Proportion of each typical speciation in PM2.5.Fullsize Image
Reducibilities of wüstite and calcio-wüstite have been examined using high temperature X-ray diffraction analysis including the effect of hydrogen on the reducibility. Fe2O3 reagent powders and hematite ore powders were used for reduction of wüstite (denoted as FeO) and sintered ore powders were used for reduction of FeO and calcio-wüstite (denoted as CW). High-temperature X-ray diffraction was applied to these samples in a flow of CO–CO2–He mixtures with and without 3.9 vol% of hydrogen during the heating cycle which simulates a blast furnace condition. The diffraction angle was scanned in the range from 33° to 55°. In experiment on sintered ore powders without hydrogen, the main peak around 48.5° shifted to lower angles with increasing temperature. This shift also continued while temperature was kept at 1000°C where wüstite was saturated with iron; on the contrary, the peak shift did not take place for hematite ore powders. This main peak is associated with wüstite (200), which is actually composed of peaks due to FeO and CW for sintered ore powders. The peak shift reflects that the peak intensity of CW increases relative to that of FeO, which suggests that the reduction of FeO proceeds faster than that of CW, and the reducibility of FeO is higher. In contrast, the peak shift did not take place in experiment on sintered ore powders with hydrogen additions. This suggests that the reducibility of CW is comparable to that of FeO in the presence of hydrogen.
The influence of MgO, Na2O, and B2O3 on the viscosity of Cr2O3 bearing CaO–SiO2–Al2O3 slags was investigated using the rotating cylinder method. Structural information of slags with different MgO, Na2O, and B2O3 content was obtained via Raman spectroscopy. The viscosity of Cr2O3 bearing CaO–SiO2–Al2O3–MgO slags increases with Cr2O3 addition. The viscosity and activation energy (Eµ) of Cr2O3 bearing CaO–SiO2–Al2O3 slags decreases with increased MgO, Na2O, and B2O3 content. The effect of MgO and B2O3 on viscosity and activation energy (Eµ) of Cr2O3 bearing CaO–SiO2–Al2O3 slags was greater than that of Na2O. This could be due to the different ways in which these additives modify the slag network structure. Raman spectroscopy analysis revealed that MgO and Na2O work as network modifiers, and the degree of polymerization (DOP) of slags increases with the addition of MgO and Na2O. MgO is more effective at modifying the structure than Na2O, because Na2O may be more likely to produce network former [AlO4] units. In this study, Cr2O3 and B2O3 are found to behave as network formers and increase the DOP. This is characterized by the decrease in NBO/Si (the number of non-bridging oxygen per Si atom) value. B2O3 addition leads to the formation of low melting point eutectics and weaker polymerization strength, which contribute to the decrease in slag viscosity.
The corrosion rate of Al2O3–SiO2 system bricks, which are practical fired bricks, into CaO–SiO2–Al2O3–MgO slag was investigated, and the effects of temperature, refractory composition and mass transfer rate in slag on the corrosion rate of the bricks were discussed. As a result, the corrosion rate decreased as the alumina content in the brick increased. The corrosion rate increased with increasing temperature. The corrosion rate decreased with decreasing rotational speed, that is, mass transfer of Al2O3 and SiO2 in the slag phase. Corrosion proceeded at the rate of 1.3 mm/min even when the rotational speed of the refractory sample was 0 rpm. Based on an analysis of the experimental results from the viewpoint of transport phenomena, under the conditions of this study, it is estimated that the reaction proceeds under a condition in which natural convection is rate-controlling for mass transfer when the rotational speed is lower than 44 rpm, in a transition region, that is, a mixed condition of natural convection and forced convection, at speeds of 44–133 rpm, and under a condition in which forced convection is rate-controlling when the rotational speed is over 133 rpm.
Aimed at the pretreatment for hot metal with varied phosphorus contents, by applying the indirect approach, the distribution ratio of phosphorus between multi phase slags with 6% to 13% P2O5, whose melting points were close to the hot metal temperature, and carbon-saturated molten iron at 1573 K, , were measured. The results demonstrated was determined by the composition of multi phase slags and that at different levels of the P2O5 content, the combination of the (FeO) content and the mass ratio of solid particles to molten slag with which reached the maximum was different. In correspondence with high-P content hot metal, under the condition of about 13% P2O5, a decrease in (%FeO) and a simultaneous increase in solid particles/molten slag mass ratio was benefit to the increase of , and the maximum reached 130. However, when P2O5 content was about 10% and 6%, could only reach 107.98 and 60.7 at most, respectively. The results of microcosmic measurements showed that in quenched multi phase slags, there exist two kinds of precipitates with different phosphorus contents, i.e. the low-P phase (6C2S-mC3P, m=0.6294~1.3400) and the high-P phase (C2S-nC3P, n=1.1064~1.4303), and also 2CaO·SiO2 phase with no phosphorus and CaO–SiO2–FetO slag.
Based on the ion and molecule coexistence theory (IMCT) and slag-metal equilibrium theory, a thermodynamic model to design the slag compositions balanced with the consumable electrode of G20CrNi2Mo bearing steel during electroslag remelting (ESR) process was developed. With this model, an equilibrium slag system of Al2O3, SiO2, MnO and FeO can be obtained quantitatively, which is favorable to decrease the extent of steel constituents oxidized by the molten slag. In order to validate the reasonability of this model, an industrial experimental with four types of slag systems was carried out in a special steel plant of China. The composition variation of Al, Si, Mn and oxygen corresponds well with deviation of Al2O3, SiO2, MnO and FeO from equilibrium, reflecting the reasonability of this model. This model could also provide some guidance for deoxidation practice during industrial ESR process. It is concluded that large deviation of measured FeO from equilibrium is a key factor leading to the Al-oxidation and oxygen increase. In order to improve the cleanliness of refined ingot, under the premise of one slag system with relatively low CaO content, a feasible means is to strengthen the protecting atmosphere or add strong oxidizer into the slag pool to suppress the FeO-activity to a minimum level, particularly during the last stage of remelting.
The Fe-bearing phase and P-bearing phase were successfully separated from a steelmaking slag by the super gravity and the separated efficiency was improved with increasing the separated time. The P-bearing phase precipitating at 1663 K was intercepted by the filter, while most residual melt went through the filter into the lower crucible to form calcium iron and aluminum and solid solution of iron, magnesium and manganese (RO phase) after centrifugal separation. Under the condition of gravity coefficient G=600 g, T=1663 K and t=15 minutes, the mass fraction of P2O5 in the P-bearing slag increased from 2.49 wt% before separation to 3.56 wt% and that of FetO in the Fe-bearing slag from 23.99 wt% to 38.67 wt%. The recovery ratio of P2O5 and FetO accounted for 82.2% and 68.5%, respectively.
In wide steel plate cooling process, the temperature distribution along width direction especially near plate edges is very important for properties and flatness of products. Therefore, the temperature distribution in the thickness and width direction should be considered by the online control model. High accuracy and quick response of control are the keys of industrial application. Due to the big cross-section of wide plate, the number of elements by traditional 2D mesh method is very large. So, it cannot have both computing speed and accuracy. To solve this problem, a novel 1.5D mesh method, which combines 1D and 2D ways, was studied in this paper. The feasibility of the proposed method was testified by the energy balance equation and experiments. Through comparison analysis, 1.5D model possesses faster speed and higher precision. In practical application, the model has a good performance on water crown and edge mask control of plate cooling to improve the temperature uniformity in the entire width direction.
The push-off test for measuring the bonding property between surfacing layers and steel base metal was developed after referring to and analysing relevant literature. The push-off test specimens were prepared with surface layers of austenite steel, alloyed steel strengthened by niobium carbide, and high-chromium, hyper-eutectic alloyed, cast iron on a 45 steel base metal by applying a consumable metal electrode arc surfacing welding process with three types of self-shielding, flux-cored, welding wires. The chemical compositions and microstructure of the final product were studied. The bonding strengths of 316, 241, and 60 MPa between three types of surfacing layers and the 45 steel base metal were obtained, after the push-off test. Additionally, the fracture path and fractograph characteristics were observed and determined.
An inorganic coating on 50CrVA spring steel was successfully fabricated by a simple and low-cost spraying technique, using bauxite, silicon carbide, sodium silicate, feldspar and phosphate binders. Experimental results showed that the weight gain of coated specimen was reduced by 67.82% and the decarburization layer of coated specimen disappeared completely at 1050°C holding for 120 min. The coating showed a reduction in decarburization of 100% at 1050°C holding for 120 min. It suggests that the coating prevented the decarburization during high-temperature treatment.
This contribution addresses the dissolution of primary M7C3 carbides and the simultaneous precipitation of nitrides during plasma nitriding of an AISI D2 tool steel. Samples of quenched and tempered D2 tool steel were plasma nitrided at 793 K (520°C) for times varying between 2.52 and 39.6 ks (between 42 min and 11 h). Microstructure and chemical composition of nitrided samples were then characterized by scanning electron microscopy and wavelength dispersive spectrometry. It was observed that nitrogen absorption induces M7C3 dissolution and simultaneous in situ precipitation of MN nitrides. Calphad computational thermodynamic simulations were carried out in order to evaluate phase stability and atomic partitioning in the microstructure. Atomic partitioning between MN and the martensitic matrix was associated with a thermodynamic metastable state. At 793 K, the negligible metallic-element diffusion inside both M7C3 and MN phases makes the metastable state kinetically favored instead of the thermodynamic stable state.
In order to establish a basis to predict fracture toughness of ferrite-pearlite steel, a two-stage investigation was performed. A 3D observation was first performed to characterize the relationship between micro-cracks and microstructures using a serial sectioning technique. Two types of micrographs before and after nital etching were taken to obtain 3D images of micro-cracks and microstructures, respectively. As a result of superposition of both the 3D images, it is found that a micro-crack initiated at ferrite-pearlite boundary and then propagated into pearlite grain. It is also found under the ellipse approximation of the micro-cracks that the distribution of major axis of micro-crack was close to that of the ferrite grain diameter and the distribution of miner axis was an intermediate between those of ferrite grain diameter and pearlite band thickness. Based on the results, we then proposed a 3D model on micro-crack with an oblate spheroid assumption of pearlite grain to quantitatively relate microstructures of ferrite-pearlite steel to the fracture stress. It was shown that the fracture stresses corrected by the proposed 3D model were 20–30% less than those evaluated by the conventional 2D model. It is expected to be caused by the reason that the accuracy of the conventional 2D model was less than that of the proposed 3D model based on the detailed 3D observation because the conventional model is based on the simplified assumption of 2D micro-crack in the 3D microstructure. Therefore, we can give a valuable basis to develop an accurate fracture toughness prediction model based on the detailed 3D observation.
The texture control of Fe–Ga solid solution alloy is examined by high temperature deformation, based on the previously suggested mechanism of high temperature deformation texture formation, “preferential dynamic grain growth (PDGG)”. As the result of uniaxial compression deformation of Fe-15 mol% Ga alloy at 1173 K, sharp alignment of <001> along the compression axis was observed. Microstructural observation by EBSD revealed that the <001> alignment was attributable to the growth of <001> oriented grains. The observed textures and microstructures were similar to those seen in the previous studies of Fe–Si alloys, in which the activation of PDGG was confirmed. Based on these facts, it is concluded that PDGG can be applied as a texture control technique for Fe–Ga alloy. The deformed sample showed larger saturation magnetostriction than the sample without deformation, indicating the effectiveness of the texture control by high temperature deformation.
Magnetostriction curves for annealed and deformed samples. The latter was compressed up to −1.9 at 1173 K with 5.0×10−4 s−1. The results under parallel (|| H) and perpendicular (⊥ H) magnetic field to the strain gauges are simultaneously shown.Fullsize Image
In this research, we analyzed electric furnace steel using the laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) method with the objective of quantitatively evaluating the concentration distributions of tramp elements present in microdomains. Point analysis was carried out for nine microdomain locations (defined as Areas) measuring 500 µm (length) × 600 µm (width) for the elements Cu, Sn, Ni, Mn, W, Cr, Mo, Ag, Pb, and B.
The highest concentration of Cu found in Area 4 was 4936 ppm, while the lowest was 674 ppm in Area 5. The correlations between Cu concentration and concentrations of other elements were analyzed for all measured points. Mo, W, Mn, Sn had correlation coefficients of more than 0.65, while Pb, Ag, Ni, B, Cr had correlation coefficients of −0.15 to +0.22. Furthermore, concentration distributions for the four elements with high correlations were analyzed for regions where the Cu concentration was more than 1.5-times the bulk concentration (5490 ppm).
Correlation of Cu concentration with those of the other measured elements.Fullsize Image