Cold bonded ore–coal composite pellets for sponge ironmaking Part 1 Laboratory scale development

Abstract

There is a need for the development of efficient industrial processes to use iron ore fines of high grade. Attention is particularly drawn to rotary kiln sponge ironmaking technology using lump iron ore, where productivity is low and energy consumption high compared with gas based processes. Fundamental studies carried out elsewhere indicate that the reduction of lump iron is accelerated if a limited amount of carbonaceous material is incorporated in the agglomerate of iron ore fines. Based on these considerations, cold bonded ore–coal composite pellets have been developed for sponge ironmaking in a rotary kiln. These composite pellets were tested in the laboratory and found to reduce very quickly, compared with lump iron ore. Composite pellets were also tested in an 8 t/day rotary kiln sponge iron plant giving enhanced productivity and lower coal consumption, and these results will be presented in Part 2 of this paper (next issue).     

Influence of bed conditions on gas flow in the COREX shaft furnace by DEM–CFD modelling

The gas flow plays an indispensable part in the production process of direct reduction iron in the COREX shaft furnace. So as to assess the gas flow under different bed conditions which are including shapes of the bed, different particle diameters and particle motion speed, a three-dimensional model has been built. The behaviour of gas flow was investigated by a hybrid model of DEM–CFD coupling. The results show that the bed void differences which is caused by the packing way and particle diameter has an important influence on the gas flow and the shaped bed of ‘V’ is the better choice to provide the optimal gas flow in the packed bed. When the descend velocity is 1 or 2?m?h^?1, it has little impact on the gas flow in the packed bed, and we can think that the bed is static.     

Effect of CaO on Fluorine in the Decomposition of REFCO3

Influence of CaO on thermal decomposition of REFCO3 was studied. The results showed that CaO did not affect significantly the decomposition ratio of REFCO3. The XRD experiment showed that there was a great deal of CaF2 in the masting production, the gas chromatographic analysis on the gas of REFCO3 decomposed, and the 70% content of fluorine in the gas of REFCO3 added 15% CaO was reduced. CaO could absorb the fluorine from the decomposition of REFCO3, and the environmental pollution of the fluorine was greatly alleviated,     

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Abstract

Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.     

Effect of iron as alloying element on electrochemical behaviour of 90∶10 Cu–Ni alloy

Abstract

Copper–nickel alloys have been used in many applications in marine environments, because of their excellent corrosion and biofouling resistance. In this study, the effects of iron as an alloying element on the corrosion behaviour of copper–10 wt-% nickel alloy in artificial saline solutions and natural sea water were investigated. Synthetic copper–nickel alloys were prepared in an induction furnace under an argon–7 vol.-% hydrogen atmosphere in cylindrical boron nitride crucibles. They were then homogenised at 950°C for 10 h under the same protective atmosphere. Linear sweep polarisation, cyclic polarisation, Tafel extrapolation and cyclic voltammetry techniques were performed in this investigation. Following the electrochemical measurements, the corrosion products and the passive film were analysed using a field emission scanning electron microscope (FE-SEM), electron probe microanalysis, energy dispersive spectrometry (EDS), wavelength dispersive spectrometry (WDS) and X-ray diffraction (XRD). The electrochemical behaviour of the synthetic Cu–Ni–Fe alloys depends on maintaining iron in a single phase in the solid solution (the maximum amount of iron that can be used was 1·5 wt-%). Quenching improves the electrochemical behaviour of synthetic Cu–Ni–Fe alloys containing relatively high iron content. The outer layer of the passive film is porous in the absence of iron, but when iron is added, the pores disappear and cracks appear. When no sulphate is present in the solution, the passive film formed on synthetic Cu–Ni–Fe alloys consists entirely of chlorides, and Fe₂O₃. In the presence of sulphate, FeS and NiS were detected in the corrosion film.

On a utilisé les alliages de cuivre–nickel à de nombreuses fins en milieux marins, grâce à leur excellente résistance à la corrosion et à l’incrustation biologique. Dans cette étude, on a examiné l’effet du fer en tant qu’élément d’alliage sur le comportement de corrosion d’un alliage de cuivre–10% en poids de nickel dans des solutions salines artificielles et dans de l’eau de mer naturelle. On a préparé des alliages synthétiques de cuivre–nickel dans un four à induction dans une atmosphère d’argon–7% en volume d’hydrogène dans des creusets cylindriques de nitrure de bore. On les a ensuite homogénéisés à 950°C pendant 10 heures sous la même atmosphère protectrice. Dans cette investigation, on a utilisé des techniques de polarisation linéaire à balayage, de polarisation cyclique, d’extrapolation de Tafel et de voltampérométrie cyclique. Après les mesures électrochimiques, on a analysé les produits de corrosion et le film passif en utilisant un microscope à balayage électronique à champs par émission d’ions (FE-SEM), la microanalyse par électrons, la spectrométrie des rayons X à dispersion d’énergie (EDS), la spectrométrie dispersive en longueur d’onde (WDS) et la diffraction des rayons X (XRD). Le comportement électrochimique des alliages synthétiques de Cu-Ni-Fe dépend du maintien du fer en une phase unique dans la solution solide (la quantité maximale de fer que l’on pouvait utiliser étant de 1·5% en poids). La trempe améliore le comportement électrochimique des alliages synthétiques de Cu–Ni–Fe ayant une teneur relativement élevée en fer. La couche extérieure du film passif est poreuse en l’absence de fer, mais lorsque l’on ajoute du fer, les pores disparaissent et des fissures apparaissent. Lorsqu’il n’y a pas de sulfate dans la solution, le film passif formé sur les alliages synthétiques de Cu–Ni–Fe consiste entièrement en chlorures et en Fe₂O₃. En présence de sulfate, on détecte du FeS et du NiS dans le film de corrosion.     

Kinetics and mechanism of smelting reduction of fluxed chromite Part 1 Carbon–chromite–flux composite pellets in Fe–Cr–C–Si melts

Abstract

Experimental studies on the smelting reduction of fluxed carbon–chromite composite pellets in Fe–Cr–C–Si alloys were carried out at 1520–1600°C. The reduction reaction was found to be favoured by high temperatures, a high lime addition in the pellets, a long pellet dissolution time, and a moderate melt Cr content. For a given CaO addition, however, the reduction rate initially slowed before increasing with an increasing silica addition to the pellets. A three stage reduction mechanism is proposed. The first stage is very likely to be controlled by solid state and/or gas diffusion with an apparent activation energy of 472 kJ mol^-1 for pellets fluxed with 15%CaO and 25%SiO₂ . The third stage proceeds via smelting mechanisms, with mass transfer in the slag phase possibly rate controlling.     

Transfer of iron to Cu–Ni alloys from the lining of the vacuum induction furnace

In Ni–Cu alloys, iron must be excluded in many cases. Iron may enter the alloy from the batch or the furnace lining. Since the Fe₂O₃ content in refractories may be as much as 2.5%, it is important to assess the increase in iron content in alloys on account of interaction with the furnace lining. In the present work, the influence of the Fe₂O₃ content in the crucible and the volume of the crucible on the iron content in the final alloy is studied. Thermodynamic analysis and experimental data indicate that the nickel and copper in Ni–Cu alloys may reduce iron that is present in the lining. When using low-iron batch, iron from the crucible is transferred almost completely to the melt. The increase in iron content in Ni–Cu alloys is investigated as a function of the capacity of the vacuum induction furnace and the Fe₂O₃ content in the periclase crucibles, with complete transfer of the iron from the lining to the melt. With increase in furnace capacity, less iron enters the melt from the crucible. With more than 200 kg of metal, the increase in iron concentration mainly depends not on the furnace capacity but on the Fe₂O₃ content in the refractory. In order to produce Ni–Cu alloys with <0.01% Fe, refractories with Fe₂O₃ content no higher than 0.5% must be used. To produce Ni?Cu alloys with <0.05% Fe, the use of lining refractories with Fe₂O₃ content no higher than 2.5% is recommended.     

Effect of TiO2 on the crystallisation behaviour of CaF2–CaO–Al2O3–MgO slag for electroslag remelting of Ti-containing tool steel

The crystallisation characteristics of CaF₂–CaO–Al₂O₃–MgO slags with various TiO₂ contents from 0 to 9.73 mass% were studied using a single hot thermocouple technique, SEM-EDS and X-ray diffraction. The crystallisation mechanism of TiO₂-bearing slag was identified based on kinetic analysis. It was found that increasing TiO₂ from 0 to 6.43 mass% inhibited the crystallisation ability of electroslag remelting-type CaF₂–CaO–Al₂O₃–MgO slag, whereas further increasing TiO₂ content up to 9.73 mass% enhanced the slag crystallisation signally. When increasing TiO₂ content to 6.43 mass%, the crystalline phase shift from CaO to Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ at high temperatures. At lower temperatures, the crystalline phase change from polygonal Ca₁₂Al₁₄O₃₂F₂ to need-like CaTiO₃. Further increasing TiO₂ content to 9.73 mass%, the crystalline phase are Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ in the range of 1473–1613?K. The crystallisation of crystalline phase in the isothermal crystallisation is surface nucleation and controlled by interface reaction when TiO₂ content is lower than 6.43 mass% in the slag. It is bulk nucleation and diffusion-controlled one-dimensional growth in slag with 9.73 mass% TiO₂.     

Increase in the efficiency of electric melting of pellets in an arc furnace with allowance for the energy effect of afterburning of carbon oxide in slag using fuel–oxygen burners

The problems of increasing the efficiency of electric steelmaking using fuel–oxygen burners to supply oxygen for the afterburning of effluent gases in an arc furnace are considered. The application of a new energy-saving regime based on a proposed technology of electric melting is shown to intensify the processes of slag formation, heating, and metal decarburization.     

Interaction of iron and aluminum in the plastic deformation and fast heating of laminar Fe–Al composite

The influence of plastic deformation and the heating rate on the solid-phase interaction of steel strip and aluminum powder is investigated. Recrystallization of the contacting materials determines the phase formation. The layer thickness of the Fe–Al intermetallides is plotted as function of the strain and heating rate. On that basis, the parameters of the transition layer may be predicted in selecting the technological conditions.     

Material expenditures in deep desulfurization of steel in the ladle–furnace unit

The desulfurization of steel in a 160-t casting ladle is investigated. On that basis, a technology for reducing the sulfur content of low-carbon and low-alloy pipe steel to 0.001–0.003% is developed. The material expenditures in deep desulfurization of steel in a 160-t ladle–furnace unit are assessed.     

Effect of Phase-Selective Nanoscale Precipitates on the Bauschinger Effect in Austenitic–Ferritic Duplex Stainless Steels

Metallurgical and Materials Transactions A - The Bauschinger effect in austenitic–ferritic duplex stainless steel 1.4462 was investigated using tension–compression tests combined with...     

Effect of the temperature–rate parameters of directional solidification on the structure formation in high-temperature materials

The effect of the temperature gradient and the crystal growth rate on the structure formation in nickel and niobium superalloys is studied under the conditions of the flat, cellular, dendritic, or dendritic–cellular configuration of a solidification front during directional solidification.     

Effect of Samarium on the Properties of Mg–Y–Gd–Zr Alloys

The microstructure, the aging kinetics, and the strength properties of Mg–Y–Gd–Zr cast alloys, in particular, a samarium-alloyed IMV7-1 alloy, at room and high (250, 300°C) temperatures after homogenization without and with subsequent aging are studied. Alloying with samarium accelerates the decomposition of the supersaturated magnesium solid solution and enhances the properties of the Mg–Y–Gd–Zr alloys.     

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Abstract

Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr₂O₃ refractories in a synthesised 50CaO–45Al₂O₃–5SiO₂ liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773?K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr₂O₃ refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75?mL·min^??1. The slag containing 5?mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.     

Effect of modification on the solidification of Al–Si aluminum alloys

The solidification of the AK12 alloy processed by a standard flux and a combined modifying flux, which significantly increases the mechanical properties of the alloy at a significant increase in the modifying effect time, is studied. The experimental results are simulated using the ProCAST software package.     

Effect of gadolinium on the properties of Pr–Dy–Fe–Co–B materials

Sintered (Pr_1–x–y Dy _x Gd _y )_13–14(Fe_1–z Co _z )_balB_6–7 materials (x = 0.18–0.58, y = 0.05–0.33, z = 0.2–0.36) have been studied. The magnetic moments of gadolinium ions and those of the sublattice formed by Fe and Co ions are shown to be ordered antiferromagnetically. It is noted that an increase in the content of gadolinium, which substitutes for dysprosium, leads to an increase in residual induction B _r , a decrease in coercive force H _cJ , and an increase in the absolute value of the temperature coefficient of induction. The opposite effect takes place in the case of substitution of gadolinium for praseodymium in materials with a fixed dysprosium content.     

Effect of the Al–Zr–Y master alloy composition on the modifying effect in the Al–4% Cu alloy

The results of modifying the Al–4% Cu alloy with test Al–1.04% Zr–0.70% Y and Al–1.23% Zr–0.39% Y master alloys are reported; the Zr-to-Y atomic-percentage ratio in the alloys is 1.41 and 3.08, respectively. The effect of small amounts of Zr and Y (from 0.1 to 0.3%) added in the form of test ternary master alloys of different compositions and binary Al–Zr and Al–Y master alloys on the grain refinement in the Al–4% Cu alloy has been studied. The structure of the initial alloy is characterized by pronounced directional solidification of the α phase. As the Zr + Y content increases, the columnar-crystal zone decreases and the equiaxed-crystal zone increases; at a (Zr + Y) content of 0.326%, only equiaxed crystals ~200 μm in size are present in an ingot. When Zr and Y are added with binary master alloys, the macrostructure of the modified Al–4% Cu alloys indicates that columnar crystals grow until their contact at the center of the ingot, and their growth is independent of the amount of added Zr and Y.     

The Effect of Composition on the Formation of a BCC Approximant in Ti–Cr–Al–Si–O Alloys

Powder Metallurgy and Metal Ceramics - The microstructure, phase composition, and mechanical properties of Ti–Cr–Al–Si–O alloys in ascast state and after annealing at...     

Effect of zirconium on the oxygen solubility in liquid nickel and Ni–Fe melts

The oxygen solubility in liquid nickel containing zirconium is studied experimentally for the first time at 1873 K. The equilibrium constants of the reaction of interaction between zirconium and oxygen dissolved in liquid nickel, the interaction parameters characterizing these solutions, and the zirconium activity coefficient in nickel at infinite dilution are found. The equilibrium constants of the reaction of interaction between zirconium and oxygen dissolved in the melt, the Gibbs energy of the reaction of interaction between zirconium and oxygen, and the interaction parameters characterizing these solutions are calculated at 1873 K for a wide composition range of Ni–Fe alloys. The oxygen solubility in various Ni–Fe melts containing zirconium is found at 1873 K. The deoxidizing capacity of zirconium increases as the iron content increases to 30% and decreases at higher iron content in the melt. This can be explained by the fact that an increase in the iron content lead to, on the one hand, a strengthening of the bonding forces of oxygen atoms in a melt and, on the other hand, to a significant weakening of the bonding forces of zirconium atoms with the base metal.