Use of Banded Hematite Quartzite (BHQ) in Blast Furnace for Partial Replacement of Quartzite

Hot metal produced through blast furnace (BF) route is still the most preferred route in majority of the steel industries. In the blast furnace operation, quartzite is used as flux to adjust the desired slag chemistry and basicity (B2 of 1–1.08) to achieve optimum slag properties such as low liquidus temperature, high Sulphur carrying capacity and low viscosity. This paper describes the investigations carried out at JSW Steel Ltd to identify alternate sources of silica other than quartzite for use as flux in BF to maintain the desired slag chemistry for smooth operation and cost reduction. Banded hematite quartzite (BHQ) ore available in Karnataka region contains 28–33% Fe, 45–46% silica, 1.3–1.5% alumina and is found suitable for use as partial replacement for quartzite in blast furnaces. Mineralogy and phase analysis of BHQ reveals alternate bands of hematite and silica whereas in lump ore, hematite and silica are uniformly distributed. This phase distribution and reducibility index of BHQ (~66%) affect the softening start temperature by forming fayalite (2FeO·SiO₂) as primary slag. Fines generations are found to be comparatively higher (from 6.3 to 6.4%) but in acceptable range. The Fe content in the BHQ also contributes to the overall Fe input to the furnace favoring an option to reduce the equivalent amount of iron bearing materials in the charge. Plant trials at JSW steel blast furnace #4, indicate an improvement in overall operational performance resulting in increased Fe input per charge, reduction in slag rate by 8 kg/thm due to low alumina input and easier achievement of final slag chemistry.     

Simulation of primary-slag melting behavior in the cohesive zone of a blast furnace, considering the effect of Al2O3, Fe t O, and basicity in the sinter ore

The alumina content in the iron ore imported to Japan is increasing year by year, and some problems in blast furnace operation, due to the use of the high-alumina-containing sinter, have already been reported. In order to clarify the mechanism of the harmful effect of alumina on the blast furnace operation, the behavior of the primary melt, which is formed in the sinter at the cohesive zone of the blast furnace, has been simulated by dripping slag through an iron or oxide funnel. The effects of basicity, Al₂O₃, and Fe _t O contents in the five slag systems on the dripping temperature and weight of slag remaining on the funnel have been discussed. It was found that the eutectic melt formed in the sinter would play an important role in the dripping behavior of the slag in the blast furnace through the fine poreosity of the reduced iron and ore particles. Al₂O₃ increased the weight of the slag remaining on the funnel, and its effect became very significant in the acidic and low-Fe _t O-containing slag. It was estimated that the increase of the weight of the slag remaining on the funnel by Al₂O₃ in the ore could result in a harmful effect on the permeability resistance and an indirect reduction rate of the sinter in the blast furnace.     

Experimental and Modeling Studies of the Lamellar Eutectic Growth of Mg-Al Alloy

Directionally solidified samples of Mg-32.3 wt pct Al eutectic alloy were produced under an argon atmosphere in a vacuum Bridgman-type furnace to study the eutectic growth with different growth velocities. Typical features such as steady-state lamellar eutectic growth, lamellar branching at the quenching interface, and the formation of colony structures due to the impurity of the Mg-Al binary alloy were observed using a JEOL 6301F scanning electron microscope (JEOL Ltd., Tokyo, Japan). The lamellar spacing of the two eutectic phases was measured on the transverse sections of the samples. It was found that the relationship between the measured lamellar spacing and growth velocity agreed well with the prediction of the Jackson-Hunt model. Subsequent studies of Mg-Al eutectic growth were conducted using a numerical model based on the cellular automaton (CA) method. Taking account of the solute diffusion, constitutional undercooling, and curvature undercooling, modeling of steady-state lamellar eutectic growth was achieved. A systematic investigation of the eutectic growth morphology and lamellar spacing of the Mg-Al eutectic was carried out under directional solidification with different undercoolings, initial lamellar spacings, temperature gradients, and growth velocities. The results showed that under the interaction between solute diffusion and surface energy, the adjustment of eutectic lamellar spacing was accomplished by nucleation, lamellar branching, lamellar termination, and overgrowth. The simulated results were consistent with both the experimental results and the Jackson-Hunt eutectic theory.     

Effect of manganese ore blends on performance of submerged arc furnace for ferromanganese production

Abstract

Manganese ore blends are used in ferromanganese production. The blend composition controls the operational performance of submerged arc furnace. A case study has been carried out at FAP, Joda, Tata Steel to better understand the process. The results of experiments revealed that the phase decomposition and decrepitation of Mn ore at low temperatures (500–900°C) in the upper part of the furnace increased the furnace top temperature and thereby promoted agglomeration of the charge, which caused the violent eruptions in the furnace. The root cause of the problems in reaction zone (bottom part) of the furnace was changes in the composition of slag, i.e. low silica and high alumina, which was also due to selection of Mn ores in the blends. Various options for silica addition were examined and compared. The pretreatment of the Mn ores and use of synthetic slag for silica adjustment options were identified to overcome the operating problems and to utilise the captive Mn ores.     

金属钆中钨的演化迁移行为与调控

以氟化钆为原料,金属钙为还原剂,在真空感应炉内,用钙热还原和XRD法研究了金属钆中钨的来源、形态、分布、演化迁移行为和调控方法。结果表明,金属钆中钨主要来源于坩埚,以熔解态钨和夹杂物Gd_2(WO_4)_3两种形态存在。钨在金属钆铸锭的下表面中心区域位置发生偏聚,含量最高,上表面二分之一半径处含量最低。演化迁移行为主要有两条途径,单质钨经脱落、熔解、熔体中迁移再分配、铸模内向中心和底部迁移;单质钨被氧化为氧化钨后,进入熔体与钆结合为Gd_2(WO_4)_3、铸模内向中心和底部迁移。从钨坩埚致密性、熔炼氛围、炉内残余氧量、原辅料纯度和升降温制度等方面调控后,可获得平均钨含量为0.008%的金属钆。     

Effect of superheating on structure of some aluminum alloys

The effect of increasing pouring temperatures was investigated on several aluminum alloys, which were frozen at various rates ranging from less than 0.01°C/s (furnace cooled) to more than 20°C/s (thin metal mold). It was found that the higher the superheat, the faster the solidification rate. Interdendritic spacing, size of primary and eutectic constituents and grain size decrease with the increasing solidification rate that results from increased superheating, in spite of the fact that the actual freezing time increases. Indications are that aluminum alloys contain a nucleant that acts at zero undercooking and that superheating up to 500°C above the freezing point reduced the size and possibly the number of nucleating particles, but does not eliminate them completely.     

Simulation of metal-matrix composite isothermal infiltration processing

In pressure infiltration processing of metal-matrix composites, molten metal is injected under external pressure into a porous preform of the reinforcing phase and solidified, either during infiltration or after the mold is filled. If infiltration is isothermal, the physics of the process are similar to drainage phenomena encountered in soil mechanics. Using this similarity, a finite-element software is developed to simulate metal-matrix composite infiltration by adaptation of a code originally developed for soil mechanics. Solutions are given for isothermal infiltration of porous preforms by a molten metal under any increasing function of the applied pressure vs time, taking into account capillary phenomena. Experimental validation is performed using SAFFIL alumina fiber preforms infiltrated with an aluminum matrix in a series of isothermal infiltration experiments in unidirectional and axisymmetric configurations. Numerical and experimental data show good agreement, both in terms of infiltration kinetics and porosity distribution. The simulation tool can, thus, be applied for isothermal infiltration of complex geometries and boundary conditions and aid mold design and process parameter optimization.     

Fe-B及Fe-C-B合金的激光熔化激冷

工业纯铁与共析碳钢表面渗硼层先在炉中处理,以获得共晶组织,然后以高能密度激光束扫描;被激光熔化的金属在冷基底的吸热作用下,以非常高的速度冷却并凝固。实验表明,炉内处理后Fe-B合金层的共晶由α-Fe+Fe₂B二相组成,FeC-B合金层的共晶由α-Fe+Fe₃(C、B)二相组成;共晶中Fe₂B为方棒状和Fe₃(C、B)为片层状。激光熔化激冷后,共晶中的相组成及形貌无改变,但棒间距和片间距相应减小了40及100倍。共晶组织的硬度大幅度增高,每个合金系的共晶组织的硬度与尺寸的关系服从Hall-Petch公式。     

Eutectic Morphology of Al-7Si-0.3Mg Alloys with Scandium Additions

The mechanisms of Al-Si eutectic refinement due to scandium (Sc) additions have been studied in an Al-7Si-0.3Mg foundry alloy. The evolution of eutectic microstructure is studied by thermal analysis and interrupted solidification, and the distribution of Sc is studied by synchrotron micro-XRF mapping. Sc is shown to cause significant refinement of the eutectic silicon. The results show that Sc additions strongly suppress the nucleation of eutectic silicon due to the formation of ScP instead of AlP. Sc additions change the macroscopic eutectic growth mode to the propagation of a defined eutectic front from the mold walls opposite to the heat flux direction similar to past work with Na, Ca, and Y additions. It is found that Sc segregates to the eutectic aluminum and AlSi₂Sc₂ phases and not to eutectic silicon, suggesting that impurity-induced twinning does not operate. The results suggest that Sc refinement is mostly caused by the significantly reduced silicon nucleation frequency and the resulting increase in mean interface growth rate.     

An analytical technique for the determination of the thermal contact resistance between a solidifying metal and mold

In the classical solution to one-dimensional solidifications Schwarz showed that in the case of perfect thermal contact the interface temperature between the mold and solidifying material is constant. Adams hypothesized that in the case of real casting problems where there is imperfect thermal contact, that one could still use the interface temperature computed by Schwarz ’s solution but now acting through a film resistance to the mold and a film resistance to the solidifying metal. The problem of solidifying a metal by a constant temperature source acting through a film resistance is solved by the method of successive approximations. The solution to the problem of a mold heated by a constant temperature source acting through a film resistance is well known. Taking experimental data for depth solidifiedvs time the first problem is solved inversely to determine the film resistance between the constant temperature source and the solidifying metal. Using experimental curves for temperaturevs depth at various times the second problem is also solved inversely in order to determine the film resistance between the mold and the constant temperature source. The overall film resistance between the mold and solidifying metal is the sum of the two resistances. Experiments indicate that the two resistances cannot be assumed equal. Formerly with GTE Labs., Waltham, MA     

Trace Elements in the Si Furnace. Part I: Behavior of Impurities in Quartz During Reduction

Quartz and carbonaceous materials, which are used in the production of silicon as well as electrodes and refractories in the silicon furnace, contain trace elements mostly in the form of oxides. These oxides can be reduced to gaseous compounds and leave the furnace or stay in the reaction products—metal and slag. This article examines the behavior of trace elements in hydrothermal quartz and quartzite in the reaction of SiO₂ with Si or SiC. Mixtures of SiO₂ (quartz or quartzite), SiC, and Si in forms of lumps or pellets were heated to 1923 K and 2123 K (1650°C and 1850°C) in high purity graphite crucibles under Argon gas flow. The gaseous compounds condensed in the inner lining of the tube attached to the crucible. The phases present in the reacted charge and the collected condensates were studied quantitatively by X-ray diffraction (XRD) and qualitatively by Electron Probe Micro Analyzer (EPMA). Contaminants in the charge materials, reacted charge and condensate were analyzed by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Muscovite in the mineral phase of quartz melted and formed two immiscible liquid phases: an Al-rich melt at the core of the mineral, and a SiO₂-rich melt at the mineral boundaries. B, Mn, and Pb in quartz were removed during heating in reducing atmosphere at temperature above 1923 K (1650°C). Mn, Fe, Al and B diffused from quartz into silicon. P concentration was under the detection limit. Quartzite and hydrothermal quartz had different initial impurity levels: quartzite remained more impure after reduction experiment but approached purity of hydrothermal quartz upon silica reduction.     

Interfacial characteristics for brazing of aluminum matrix composites with Al-12Si filler metals

Discussions concerning the interfacial reactions and characterizations in brazing aluminum matrix composites are documented in this study. Joints of alumina particulate reinforced 6061 aluminum matrix composites were made using an Al-12 (wt pct) Si filler metal by vacuum brazing. The resulted maximum bonding strengths were 75.4, 81.5, and 71.8 MPa for 10, 15, and 20 vol pct alumina reinforcement, respectively. The microstructural examinations revealed that the bonding strength was strictly related to the reinforced alumina particles and the reaction products presented at the joint interfaces. During brazing, Mg segregated at the joining interface and alumina/6061 Al interface. Further, reactions between alumina and 6061 Al matrix resulted in the formation of Mg-rich phases, such as MgAl₂O₄ and MgO, near the joining interface and the alumina reinforcement. The Si in the filler material penetrated into the metal matrix composites (MMCs) matrix and segregated at the alumina/6061 Al interfaces. This phenomenon can be confirmed by a joint between two alumina bulk specimens.     

An analytical technique for the determination of the thermal contact resistance between a solidifying metal and mold

In the classical solution to one-dimensional solidifications Schwarz showed that in the case of perfect thermal contact the interface temperature between the mold and solidifying material is constant. Adams hypothesized that in the case of real casting problems where there is imperfect thermal contact, that one could still use the interface temperature computed by Schwarz’s solution but now acting through a film resistance to the mold and a film resistance to the solidifying metal. The problem of solidifying a metal by a constant temperature source acting through a film resistance is solved by the method of successive approximations. The solution to the problem of a mold heated by a constant temperature source acting through a film resistance is well known. Taking experimental data for depth solidifiedvs time the first problem is solved inversely to determine the film resistance between the constant temperature source and the solidifying metal. Using experimental curves for temperaturevs depth at various times the second problem is also solved inversely in order to determine the film resistance between the mold and the constant temperature source. The overall film resistance between the mold and solidifying metal is the sum of the two resistances. Experiments indicate that the two resistances cannot be assumed equal. E. F. FASCETTA, formerly with GTE Labs., Waltham, MA,     

Automatic control of the carbon potential of furnace atmospheres without adding enriched gas

An approach has been proposed in this article for controlling the carbon potential of furnace atmosphere without the need to add enriched gas for the sake of simplifying the process of carbon potential control and consequently lowering the cost of atmosphere. The atmosphere was generated by reacting an N₂ + H₂O mixture with hot charcoal. An oxygen sensor and a computer were used for controlling the carbon potential of the atmosphere through controlling the temperature of charcoal instead of adding an enriched gas to the atmosphere. The control result was evaluated from (a) the stability of oxygen partial pressure of the furnace atmosphere and (b) the equilibrium carbon content of the steel heated in the furnace atmosphere. The result of controlling carbon potential with this method was indicated by observed experiments to be satisfactory;i.e., the deviation of carbon potential was below 0.06 pct. There was especially no need to add enriched gases to the atmosphere.     

Crystallization studies in the aluminum-rich corner of the aluminum-iron-manganese system

A method for determining the compositional areas of primary crystallization of Al-Fe-Mn alloys has been developed and used for the determination of the locations of the eutectic troughs, the ternary eutectic point, and the corresponding variation in composition of the FeAl₃ and (FeMn)Al₆ phases in the aluminum-rich corner of this system. The method uses slow crystallization in a relatively large and well stirred bath of alloy while periodically taking small samples of slurry at temperature by sucking these into silica tubes, followed by quenching and metallographic and electron probe examination. Growth of individual rounded aluminum and polygonal intermetallic crystals was observed during crystallization along the eutectic troughs.     

Concept of combined heating of scrap in shaft arc steel-melting furnaces

The modern limiting concentrations of harmful substances released in atmosphere are presented for steelmaking. The conditions of heating and gas formation in heating of metal scrap in a shaft arc steel-melting furnace are considered. A method of combined heating of metal scrap is proposed for such furnaces to decrease the pollutant emission into the atmosphere. Apart from the heat of effluent gases from a furnace, this method uses the heat of gas-oxygen burners placed in various shaft heater zones. The advantages of this method of heating of metal scrap are presented.     

铝硅比对烧结成矿特性及冶金性能的影响

Al2O3和SiO2是复合铁酸钙的重要组分,适宜的铝硅比是获得良好烧结成矿特性和冶金性能的重要条件.基于某钢厂现场烧结原料结构,运用FactSage理论计算了烧结体系的平衡物相组成及液相组分变化规律,随着铝硅比由0.41降至0.34,烧结矿中液相、铁氧化物等优质物相含量增加,尖晶石等劣质物相含量下降,且液相中析出复合铁...     

Effect of Ag Content on the Microstructure and Crystallization of Coupled Eutectic Growth in Directionally Solidified Al-Cu-Ag Alloys

A series of coupled eutectic growths along the univariant eutectic groove in the ternary Al-Cu-Ag alloy was studied to investigate the effect of Ag on the microstructure and crystallization of directionally solidified Al-Cu-Ag alloys. The results indicated that the eutectic morphology and orientation relationship (OR) between eutectic phases were modified as the Ag content in the Al-Cu-Ag alloys increased. At a lower growth velocity (R ≤ 1 μm/s), a banded structure formed and the interlamellar spacing decreased with the increasing Ag content. At a higher growth velocity (R ≥ 3 μm/s), the eutectic cell spacing decreased with increasing Ag content. Increasing the Ag content in the Al-Cu-Ag alloys enhanced the enrichment of the Ag solute in the liquid ahead of the quenched liquid/solid interface. In addition, increasing the Ag content in the Al-Cu-Ag alloys promoted the transformation from a “Beta 6” OR to an “Alpha 4” OR between eutectic phases. Modifications of the eutectic morphology and the OR during directional solidification were attributed to the enrichment of Ag content at the solid/liquid interface and the changes in the interfacial energy due to the increase in Ag solubility in the α-Al phase.

     

Effect of microstructure on mechanical properties of as-cast Mg-Al alloys

The mechanical properties of Mg-Al alloys are mainly determined by the microstructure, i.e., the amount and morphology of the phases, but also by the presence of defects arising from the melt handling and casting process. In order to obtain information about the isolated effect of the microstructure, it is, therefore, necessary to minimize the amounts of defects. In this study, this has been achieved by remelting and solidifying the alloys in a gradient furnace. The drawing rate was varied from 0.3 to 6 mm/s, which yielded a wide variety of microstructures. Three samples were produced for each parameter set, in order to have a statistical basis for the evaluation. The results showed that homogeneous and reproducible samples could be produced, and that the tensile properties obtained showed a very small scatter. The effects of microstructural parameters such as grain size, secondary dendrite arm spacing (SDAS), eutectic fraction, and eutectic morphology on the yield strength, ultimate tensile strength (UTS), fracture elongation, and hardness has been investigated.