Thermodynamics of Composition Control of CaO‐MnO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel

The effect of oxide component content on the low melting point zone (simplified as LMP) in the CaO‐MnO‐Al₂O₃‐SiO₂ system has been analysed by FactSage. The contents of [Si], [Mn], [O] and [Al] in liquid steel which are in equilibrium with the LMP inclusions in the CaO‐MnO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MnO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the CaO content is 15%, and that the LMP zone becomes wider with increase in SiO₂ and MnO contents (within the range of 0~25%). To obtain LMP inclusions (below 1400°C), [Si] and [Mn] can be controlled within a wide range, but [Al] and [O] must be controlled within the range of 0.5~5 ppm and 50~120 ppm, respectively.     

Composition Control of CaO‐MgO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel ‐ a Thermodynamic Analysis

The effect of oxide component content on the low melting point zone (LMP) in the CaO‐MgO‐Al₂O₃‐SiO₂ system has been analysed using FactSage software. The contents of dissolved elements [Si], [Mg], [O] and [Al] in liquid steel in equilibrium with the LMP inclusions in the CaO‐MgO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MgO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the MgO content is 10%. The LMP zone becomes wide with the increase in CaO content (within the range of 0~30 mass%) and the decrease in SiO₂ (from 25 to 5 mass%). To obtain the LMP (below 1400°C) inclusions, the [Mg], [Al] and [O] contents must be controlled within the range of 0.2~2 ppm, 1.0~2.0 ppm and 60~100 ppm, respectively.     

Viscosities of the Quaternary Al2O3‐CaO‐MgO‐SiO2 Slags

Viscosities of some quaternary slags in the Al₂O₃‐CaO‐MgO‐SiO₂ system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub‐systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso‐viscosity contours in the Al₂O₃‐CaO‐MgO‐SiO₂ system relevant to ladle slags were calculated at 1823 K and 1873 K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.     

Effects of Influencing Factors on Distribution Behaviors of Vanadium between Hot Metal and FeO‐SiO2‐MnO (‐TiO2) Slag System

The distribution behavior of vanadium between a hot metal and a FeO‐SiO₂‐MnO (‐TiO₂) slag system was studied under laboratory conditions, together with the effects of influencing factors such as temperature, slag composition, the ratio of slag to hot metal, and the initial Si and/or Ti content in hot metal. The results suggested that in a ternary FeO‐SiO₂‐MnO slag system, with an increase in temperature and an increase in the SiO₂ content of slag, the extraction ratio ($\eta _{V} $ ), distribution ratio of V ($L_{V} $ ) and the vanadium capacity of the slag ($C_{VO_{3} {}^{3{-} } } $ ) decreased, while the effect of MnO content in slag showed a different tendency under different situations. For both high and low ratios of slag to hot metal, the extraction ratio of V reached its maximum value under slag compositions of 13%–25% MnO and 10%–24% SiO₂, which correspond to the regions with lower melting point and lower viscosity of the slag. In a quaternary FeO‐SiO₂‐MnO‐TiO₂ slag system,$\eta _{V} $ ,$L_{V} $ , and $C_{VO_{3} {}^{3{-} } } $ decreased, while the activity coefficient of V₂O₃ increased, as the TiO₂ content increased. Further, the data suggested that under laboratory conditions the effects of influencing factors on the extraction ratio of V from hot metal decreased in the following order: final slag composition > temperature > initial Si and/or Ti content in hot metal.     

Water Capacity Model of Al2O3‐CaO‐MgO‐SiO2 Quaternary Slag System

The focus of the present work was to develop a water capacity model for the quaternary slag system Al₂O₃‐CaO‐MgO‐SiO₂. In the model, a silicate melt was considered to consist of two ion groupings, viz. cation grouping and oxygen ion. The water capacity of a melt is supposed to depend on the interactions between the cations in the presence of oxygen ions. These interactions were determined on the basis of the experimentally measured water solubility data. Only binary interactions were employed in the model. For the system CaO‐SiO₂, disagreement in the literature data was found. Since the interaction between Ca²⁺ and Si⁴⁺ would play an important role, experiments were carried out to determine the water capacities of some CaO‐SiO₂ slags. For this purpose a thermogravimetric method was employed. Iso‐lines of water capacities at constant MgO contents were predicted by the model and compared with the experimental data from literature. The model calculations agreed well with the experimental results.     

Study of Boronizing Mechanism of High‐Alumina Slag

As the Al₂O₃ content of the iron‐making raw materials increasing, the Al₂O₃ content in the slag increases as well, which is the certain result in the development of the iron‐making process. Based on the slag which was from the 2# blast furnace in Hebei Qianan of China, 7 different kinds of B compositions were added. The viscosity values of the CaO ‐MgO‐Al₂O₃‐SiO₂‐B₂O₃ system were measured by using the torque. The SEM and EDS apparatus were used to observe the variation characteristics of the boronizing slag of the blast furnace. Viscosity mechanism model of the boronazing high‐alumina slag was got from the analysis of the EDS compositions. These detailed analysis including the influence on the slag forming components result from different B contents which shows the conclusion that the suitable B content makes good to the viscosity, melting temperature and stability of high‐alumina slag.     

Influence of SiO2 Addition on the Properties of Al2O3‐CaO‐CaF2 Slag

The Al₂O₃‐CaO‐CaF₂ slag system is used in making special quality steels by the electro‐slag re‐melting process (ESR). The purpose of our investigation was to analyse ESR slag that contained SiO₂. The slag samples with different SiO₂ fractions (0 ‐ 20 mass %) were examined by chemical analysis, differential thermal analysis, simultaneous thermal analysis, X‐ray diffraction, electron microscopy and wetting angle measurement. With addition of SiO₂ the polymerization of slags was increased due to the formation of new silicate complex compounds that influenced their melting points and wetting angles.     

MgO Saturation in Secondary Metallurgical Lime‐aluminate and Lime‐silicate Slags

This paper provides an informative basis on MgO saturation in secondary metallurgical slags by conducting thermo‐chemical calculations in the ternary base system Al₂O₃‐CaO‐SiO₂ at 1600 °C, 1650 °C and 1700 °C using FactSage^TM6.0. The results for lime‐aluminate and lime‐silicate slag are displayed in a straightforward and illustrative manner. In addition, approximate equations describe the temperature dependencies: a temperature rise of 50 °C increases the MgO saturation limit by about 1 wt. %.     

Activity of Chromium Oxide in CaO‐SiO2 based Slags at 1873 K

Thermodynamic properties of chromium oxides in molten slags are very important for optimization of stainless steel refining processes as well as reduction processes of chromium ores. The solubility of chromite into molten slags has been found to vary drastically with oxygen partial pressure and slag composition in the former studies by the authors. In the present study, activity data and redox equilibria of chromium oxides measured under moderately reducing conditions, P_O2= 6.95×10^?11 atm, at 1873 K are summarized. For the CaO‐SiO₂‐CrO_x system, the activity coefficient of chromium oxide increased with increasing basicity and the optimized slag composition for stainless steel refining is assessed as that saturated with CaCr₂O₄ and Cr₂O₃ using the phase relations determined. On the other hand, the presence of MgO and Al₂O₃ brings about different behaviour of chromium oxide activity and redox equilibria and the 44 mass per cent CaO ‐ 39 mass per cent SiO₂ ‐11 mass per cent Al₂O₃ ‐ 6 mass per cent MgO slag is recommended to reduce the chromium oxidation loss in the practical stainless steel refining process at 1873 K.     

A Study of Microstructure and Performance of Quenching Fe‐V‐W‐Mo Alloy

The critical points and time temperature transformation (TTT) curves of Fe‐5%V‐5%W‐5%Mo‐5%Cr‐3%Nb‐2%Co (Fe‐V‐W‐Mo) were measured, and the effects of quenching temperature and cooling modes on the microstructure and performance of Fe‐V‐W‐Mo alloy were investigated. The results showed that the hardness of Fe‐V‐W‐Mo alloy increased until the quenching temperature reached 1025°C and dropped down as the quenching temperature exceeded 1050°C in oil cooling. The hardness obtained in air cooling and spray cooling exhibited a similar tendency as that in oil cooling, but the temperature at which the highest hardness was obtained in these slower cooling processes changed to a higher range. The hot hardness and toughness of Fe‐V‐W‐Mo alloy increased with rising quenching temperature until it reached 1150°C, and from then on the toughness began to drop. The main reasons why the structures and properties of Fe‐V‐W‐Mo alloy obviously change under different quenching conditions are particularly analysed at last.     

Study of New On‐Line Pre‐Hardening Technology of 3Cr2NiMo Plastic Die Steel

The thermal property parameters of 3Cr2NiMo plastic die steel were tested and the two‐dimensional finite element model was established in the paper. The temperature fields of 3Cr2NiMo plastic die steel plate with the thickness of 130 mm were calculated and analyzed under three quenching processes. The results showed that for all of the three processes the cooling rates could avoid the pearlite transformation zone when the temperature of the steel plate was more than 500°C. When the temperature was less than 500°C, the cooling rate of the third process was slower, and the temperature difference was effectively alleviated, which avoided large transformation stress appearance. For 3Cr2NiMo plastic die steel with the thickness of 130 mm, the third process was the best process. In the paper, the hardness and the microstructures were tested after the third process and tempering. After tempering process, the structures were all tempered sorbite, and the tempering hardness difference in the whole steel plate was less than 3HRC, and there were no cracks. The study provided references for on‐line pre‐hardening process formulation and optimization of large plastic die steel.     

New Methods for In‐Situ Determination of Iron Oxide in Steelmaking Slags

Although iron oxide is the most important component of steelmaking slags, no reliable technique for its in‐situ determination has been established yet. This paper however, presents data on the effect of iron oxide on the electrical conductivity of CaO‐SiO₂‐FeO‐Fe₂O₃ melts, and on limiting current and impedance in direct current or alternating current charge transfer at iron electrodes. The strong influence of iron oxide content can be utilized for in‐situ determination of total iron oxide content and Fe³⁺/Fe²⁺ ratio. The possible probe designs are presented and the principles and procedures of the measurement are explained.     

A Study of Microstructure and Performance of Tempered Fe‐V‐W‐Mo Alloy

Influences of tempering temperature, holding time and tempering times on the microstructure and performance of Fe‐5%V‐5%W‐5%Mo‐5%Cr‐3%Nb‐2%Co(Fe‐V‐W‐Mo) were investigated by means of metallography, optical microscopy, hardness measurements, impact tester and pin abrasion tester. The results show that the hardness of Fe‐V‐W‐Mo alloy remains constant when tempered below 350°C. The hardness decreases gradually as the tempering temperature increase until around 475°C and then it increases again to a peak at 525°C. The hardness of Fe‐V‐W‐Mo alloy reaches nearly the highest value after the first tempering and decreases after triple‐tempering. The toughness of Fe‐V‐W‐Mo alloy increases until the tempering temperature reaches 475°C and then decreases until the temperature reaches 525°C. However, it increases again when tempering is beyond that temperature. The excellent wear resistance can be obtained by tempering at 500‐550°C.     

Integration of the Blast Furnace Route and the FINEX®‐Process for Low CO2 Hot Metal Production

The blast furnace is the most important process for the production of hot metal. An integral part of this process route is the coking of coal and sintering of fine ore. The FINEX®‐process is a new technology for hot metal production which uses untreated fine ores and coal instead of sinter and coke. This paper deals with the investigation of integration concepts of the blast furnace and FINEX®. Low reduced iron (LRI) and/or reducing gas are/is produced in FINEX® and are/is considered as substitute/s of burden and fuel in the blast furnace, respectively. In the article the overall fuel demand and CO₂ emissions for the integration of the blast furnace and FINEX® are shown. For that reason two case studies for the integration are carried out and compared with the base case, that is, the two‐independent processes. The CO₂ emissions are calculated considering the fuel and electric power consumption of the different cases.     

Sulphide Capacities of CaO‐SiO2‐Al2O3‐MgO Slags

In Japanese steelworks, hot metal is now being produced by a scrap melting process. With this process, removals of sulphur is very much handicapped because of very high sulphur levels (0.04‐ to 0.09‐ pct by weight) and relatively low tapping temperatures (1623 to 1723 K). In order to overcome such handicaps, the authors explored on the respective phase diagrams. These explorations revealed that {CaO‐SiO₂‐Al₂O₃‐MgO} slags with Al₂O₃ contents of 30‐ to 35‐pct by weight would be good candidates as reagents for sulphur removal from high sulphur hot metal at relatively low temperatures. For better understanding of the thermodynamic properties of the candidate slags, in this study, sulphide capacities were determined through gas/slag equilibrium technique. The experimental results suggest that there would be, at least, a “window” to remove sulphur from high sulphur hot metal as relatively low temperatures.     

Minimizing the Distortion of Steel Profiles by Controlled Cooling

A complex thermomechanical model is introduced for the simulation of the transient fields of temperature and stresses during the quenching of steel products. The material behaviour is an extension of the classical J₂‐plasticity theory with the extension of temperature and phase fraction dependent yield criteria. The coupling effects, i.e., dissipation of mechanical energy, transformation induced plasticity (TRIP), and phase transformation enthalpy, are considered. The model is used for the determination of the optimal cooling or quenching for reducing the distortion in the long steel profiles. The simulation results are presented in order to investigate the effects of material properties, boundary conditions, profile size and geometry. In the simulations, L‐, T‐ and U‐profiles made of steel C45 and steel C80 are considered. It is demonstrated that with a higher cooling rate in the mass lumped regions of the profiles, the distortion can be reduced.     

The Influence of SiO2 on the Extraction of Ti Element from Ti‐bearing Blast Furnace Slag

The present paper investigated the crystallization behavior of Ti‐concentrating phases in titanium‐bearing blast furnace slags influenced by the silica content. The objective was to recycle the titanium from titanium‐bearing blast furnace slags by enriching Ti element in anosovite. The effect of SiO₂ on the formation of anosovite in the titanium‐bearing blast furnace slags was studied under C/CO equilibrated atmospheres using a combination of X‐ray Diffraction (XRD) and Energy Dispersive X‐ray Spectroscopy (EDX). It was found that, under the C/CO equilibrated atmospheres, the formed primary phases transformed from perovskite to anosovite by adding SiO₂ up to 35 wt% in the slags. The related mechanism was investigated according to the theory of molten slags structure and the principle of thermodynamics.