Showing papers in "Isij International in 2005"

Ultra-high-strength Bainitic Steels

Abstract: The authors acknowledge financial support from the Spanish Ministerio de Educacion y Ciencia for the financial support in the form of Ramon y Cajal contracts (RyC 2002 and 2004 respectively). Some of this work was carried out under the auspices of an EPSRC/MOD sponsored project on bainitic steels at the University of Cambridge; we are extremely grateful for this support over a period of three years. The authors are extremely grateful to Prof. H. K. D.

Effect of Austenite Grain Size on the Morphology and Crystallography of Lath Martensite in Low Carbon Steels

Abstract: The crystallography, microstructure and mechanical property of as-quenched martensite of Fe-0.2C-Mn(-V) alloys of which the prior austenite grain sizes are 370-2 μm were studied. The prior austenite grain, whose size is larger than 28 μm, is divided by several packets. Those packets are subdivided by blocks containing sub-blocks, each of which corresponds to the Kurdjumov-Sachs variant. When the prior austenite grain size is about 2 μm, one packet tends to grow predominantly. Each packet is divided by blocks containing sub-blocks.

Image Quality Analysis: A New Method of Characterizing Microstructures

Abstract: Polycrystalline aggregates are comprised of three microstructural features: grain centers, grain boundaries, and regions affected by grain boundaries. It is these features that determine the mechanical properties, and any advanced understanding of microstructure-property relations requires their quantitative description. Traditionally, descriptions of microstructures have been based on visualization, i.e., how grains appear in the optical or scanning electron microscope (SEM). While this may lead to classification systems that permit differentiation, it does not allow for quantification, especially in complex microstructures, and does not lend itself to either developing or applying structure-property relationships. The goal of this paper is to present a new approach to the characterization of complex microstructures, especially those found in advanced modern high strength steels. For such steels, the new approach employs the fact that different types of ferrite formed at different transformation temperatures have different dislocation or sub-grain boundary densities. Hence, measuring the degree of lattice imperfection of the grain centers of the ferrite is one way of first identifying, then grouping, and finally quantifying, the different types or forms of ferrite. The index chosen in this study to distinguish the degree of lattice imperfection is the image quality (IQ). Finally, as part of the new approach a procedure has been developed to improve the accuracy of applying IQ measurements.

Refining of Si by the Solidification of Si-Al Melt with Electromagnetic Force

Abstract: Aiming at the development of Si solidification refining process with Si-Al melt, investigations on separation method of Si grains solidified from Si-Al melt and the laboratory scale refining test were carried out. By the use of electromagnetic force under the fixed alternating magnetic field, solidified Si grains were successfully agglomerated in the Si-Al alloy and the high Si density part was obtained, although the use of gravity force was not effective. Furthermore, the refining test with induction heating revealed the high purification ability of this refining.

Kinetic analysis of the iron oxide reduction using hydrogen-carbon monoxide mixtures as reducing agent

Abstract: The kinetics of the reduction of hematite pellets using hydrogen-carbon monoxide mixtures as reducing agent was described by using the "grain model". This model involves the particle size and the porosity of the pellet asmain structural parameters which affect directly the kinetics of the hematite pellets during the reduction process. The predictions of the model were compared with the experimental results. Fired hematite pellets were reduced at 850°C using hydrogen, carbon monoxide and Midrex gas. The weight loss technique was used to follow the reduction process. The reduction of iron oxide pellets using hydrogen or carbon monoxide is a mixed controlled system, where chemical reaction and internal gas diffusion are competing processes during the first stage of the reduction, while internal gas diffusion becomes controlling step at the last stage of the process. The reduction of iron oxide pellets using Midrex gas is a mixed controlled system throughout the whole reduction process.

Prediction of Silicon Content in Blast Furnace Hot Metal Using Partial Least Squares (PLS)

Abstract: Multivariate modeling has gained popularity in several process industries, especially in the petrochemical sector. The Partial Least Square (PLS) is one of the various multivariate techniques where the relationship between multiple Y (responses) and large number of X variables (predictors) are modelled. Recently, the technique has been used in the steel industry. 1‐4) The PLS is emerging as the most robust 4,5) and reliable prediction tool when huge amounts of collinear data are to be handled. Collinear data means any two columns in the data set are linearly dependent and the inverse of the matrix is non-existent since the determinant is zero. The other multivariate techniques like multiple linear regression (MLR) fails to handle collinear data as it involves inversion of matrix to estimate the regression coefficients. The present work deals with the application of PLS to predict the silicon content of hot metal. This is a novel application of PLS in ironmaking since PLS has traditionally been used in many other scientific fields like chemometrics, chemistry, biology etc. to name a few. 5,6) Use of PLS in hot metal silicon prediction is a novel application since most of the reported Si prediction models have employed ANN 7‐10) and nonlinear time series methods. 11‐13)

Development of Fluoride-Free Fluxes for Billet Casting

Abstract: More than 90% of the world's steel is produced using the continuous casting process, a method that has seen enormous advances over the last forty years. Mould fluxes play an important part in this process. These fluxes contain fluorides, which can volatilize at operational temperatures polluting both the plant air and cooling water. Airborne fluoride could potentially be a health and safety issue. Waterborne fluoride forms hydrofluoric acid (HF), which can cause plant corrosion, and may lead to contamination of watercourses necessitating water treatment schemes. This adds to production costs and may present potential environmental hazards. These concerns could be reduced or eliminated by removing fluoride from mould fluxes.The present study examines the effect of different fluxing agents upon key mould flux properties. When substituting fluorides for alternative fluxing agents the key design properties of the fluoride-containing flux must be replicated; namely, (i) flux viscosity at 1300°C, (ii) break temperature and (iii) percentage of crystallinity in the solid slag layer. This is to ensure ‘optimal casting’ where operational problems, such as sticker breakouts and defects such as longitudinal cracking, are minimized. In addition, the quality of the steel should not be affected by the substitution. Therefore, any substitute/additive or combination of additives would have to possess the capacity to replicate the effects that fluorine has on mould flux behaviour.This study focuses on B2O3 and Na2O as alternative substitutes for CaF2 in billet fluxes. The new flux has been successfully tested in a plant trial on a continuous casting plant.

Improvement in Blast Furnace Reaction Efficiency through the Use of Highly Reactive Calcium Rich Coke

Abstract: A method to produce coke in ‘lump’ form with high strength and reactivity through the addition of a catalyst was investigated in order to improve blast furnace reaction efficiency. The addition of Ca compounds to coal before carbonization was found to considerably increase the reactivity of the coke at a low temperature range in the thermal reserve zone of a blast furnace. Furthermore it was proved that strong, highly reactive ‘lump’ form coke could be produced by adding a Ca-rich non-caking coal and adjusting the coal blend composition. Based on this fundamental study, the Ca-rich coke was successfully produced in coke ovens on a commercial scale, both at Kimitsu and Muroran works. The use of the Ca-rich coke in the Muroran No. 2 blast furnace was found to cause a decrease in the reducing agent rate by 10 kg/t-p. This technology, producing coke of high reactivity and strength through catalyst addition, is promising as a means of improving the reaction efficiency of a blast furnace.

Microstructural Changes and Crack Initiation with White Etching Area Formation under Rolling/Sliding Contact in Bearing Steel

Abstract: Microstructural changes during the formation of White Etching Area (WEA) were investigated using a rolling/sliding contact fatigue test machine. In particular, interfaces between WEA and retained austenite or spherodized carbide in a high carbon chromium bearing steel have been observed. Fatigue tests were carried out by means of a disk on roller-type equipment. It was found that acicular structures are formed at an initial stage of the WEA formation process. Plastic deformations of spherodized carbides were caused by shear stress in the initial stage of this process as well. Additionally, micro voids were found near the interfaces. Furthermore, amorphous-like structures were found in the WEA. It was suggested that WEA formation is caused by the local plastic deformation of the material. The shear stress was caused by slipping between the roller and the disk. As a result, it was suggested that martensite forms an amorphous-like phase and then changes into a WEA. Cracks developed in the amorphous-like structure/the granular area interface in the WEA and in the Matrix/WEA interface.

Discrete Particle Simulation of Solid Flow in a Model Blast Furnace

Abstract: This paper reports a numerical study of solid flow in a model blast furnace under simplified conditions by means of discrete particle simulation (DPS). The applicability of the proposed DPS approach is validated from its good agreement with the experiment in terms of solid flow patterns. It is shown that the DPS is able to generate a stagnant zone without any need for any arbitrary treatment, and capture the main features of solid flow within the furnace at a microscopic level. The results confirm that the solid flow in a blast furnace can be divided into four different flow regions. However, the flow is strongly influenced by the front and rear walls in a 2D slot model furnace whereas the predicted stagnant zone decreases significantly with wall sliding friction. In a 3D model with periodic boundary conditions incorporated, a smaller stagnant zone is obtained. The effects of solid flow rate, particle properties such as sliding and rolling friction coefficients on the solid flow are also investigated. The results are analysed in terms of solid flow patterns, solid velocity field, porosity distribution and normal force structure. The implication to blast furnace operation is discussed.

Microstructure and Formability of Aluminum Bearing TRIP-Aided Steels with Annealed Martensite Matrix

Abstract: The effects of aluminum content on microstructure, ductility and formability of advanced high strength low alloy TRIP (Transformation-Induced Plasticity)-aided ferrous sheet steels with annealed martensite matrix (or TRIP-aided annealed martensitic steel) were investigated in order to realize hot-dip galvanization. Aluminum addition of 0.5-1.0 mass% (and simultaneous silicon removal of the same amount) to a 0.2C-1.5Si-1.5Mn-0.04Al (mass%) steel refined the matrix structure and retained austenite needles and increased carbon concentration of retained austenite. It also brought on an excellent total elongation, stretch-flangeability and bendability, although the tensile strength decreased. Optimum austempering temperature for the total elongation increased to 450-475°C, due to the increased carbon concentration of retained austenite. On the other hand, optimum austempering temperatures for the stretch-flangeability and bendability were maintained at 350-400°C, mainly due to uniform fine lath matrix and retained austenite needles. If only large total elongation is required for the TRIP-aided steel, it is expected that hot-dip galvanizing immediately after continuous intercritical annealing can be realized.

Degradation Behaviour of a High CSR Coke in an Experimental Blast Furnace: Effect of Carbon Structure and Alkali Reactions

Abstract: A high CSR coke was tested in the LKAB’s Experimental Blast Furnace (EBF) at Lulea. The evolution of physical and chemical properties of the centre-line coke samples were analysed by Light Optical Microscopy (LOM), BET N2 absorption and SEM/XRF/XRD. Alkali distribution in the EBF cokes was examined by XRF/SEM and EDS. Thermo Gravimetric Analysis (TGA) was used to measure isothermal and nonisothermal CO2 reactivity of the cokes. The crystalline order of carbon and the concentration of alkalis were found to increase as the coke descended through thermal reserve zone to the cohesive zone of the EBF. The crystallite height (Lc) of EBF coke carbon displayed a linear correlation with the measured EBF temperatures demonstrating the strong effect of temperature on carbon structure of coke in the EBF. Alkali concentration of the coke was increased as it descended into the EBF, and was uniformly distributed throughout the coke matrix. The CO2 reactivity of lower zone cokes was found to increase when compared to the reactivity of the upper zones cokes, and was related to the catalytic effect of increased alkalis concentration. The deterioration of coke quality particularly coke strength and abrasion propensity were related to coke graphitisation, alkalization and reactivity. Coke graphitisation is shown to have a strong influence on the coke degradation behaviour in the EBF.

Lattice constant of iron and austenite including its supersaturation phase of carbon

Abstract: Electrolytic iron powder was heated into γ-iron phase and carburized in austenite and its supersaturation phase under the gas mixture of CO and CO2 with carbon activity of 0.1 to 1.0. The spacing of lattice planes of iron was measured using a high temperature X-ray diffractometry (XRD), which gradually increased with time and arrived at a constant value. The carbon concentration in samples after experiment was measured by a combustion-infrared absorptiometry. The lattice constants, a0 (nm), of α-iron, γ-iron and austenite including its supersaturation phase of carbon have been determined as follows;α-iron: a0=1.602×10-9T2+2.059×10-6T+0.2860 (295 to 1183 K)γ-iron: a0=8.1593×10-6T+0.35519 (1183 to 1550 K)Austenite: a0=0.35519+8.1593×10-6T+1.7341×10-3C (0 to 3.35 masss% and 1452 to 1550 K)where T and C are temperature (K) and carbon concentration (mass%), respectively.

Structure Analysis of Coke, Wood Charcoal and Bamboo Charcoal by Raman Spectroscopy and Their Reaction Rate with CO2

Abstract: In order to discuss the reactivity of carbonaceous materials with CO2, the Raman spectroscopy analysis was carried out. Nine kinds of materials were examined. The Raman spectra of ordered materials could be assigned to the graphite structure and its defect, but those of disordered materials could not. New parameters were derived to evaluate the structure of the latter. Using the parameters, the structure change was followed during high temperature heat treatment. The disordered material consists of random structure, graphite structure and its defects. The random structure changes to the graphite structure with many defects and the defects decrease with the heat treatment temperature. The reaction rate constant is evaluated. It increases when the structure changes from the random structure to the graphite structure with many defects. After the change, it decreases with decreasing the defects in graphite structure. Thus, the most reactive material should consist of the graphite structure with many defects.

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

Abstract: A study of the elastic response before and after tensile plastic strain was undertaken for two commercial low-alloyed TRIP steels. These steels, TRIP 700 (C-Mn-Al alloy) and TRIP 800 (C-Mn-Si) are commercial alloys used in sheet metal stamping. The behaviour of the instantaneous tangent modulus (ET) versus stress during loading and unloading was measured for each degree of prestrain. Loading curves show a decrease in the ET of the deformed samples as compared with the underformed state. Though at low stresses a highly linear response was measured for both steels, a decrease was obtained for TRIP 700 as strain increased, whereas TRIP 800 remained unchanged. During unloading, a progressive decrease in ET was obtained in all deformed states, with lower chord modulus values as the tensile plastic prestrain increased. The inelastic response observed is attributed mainly to microplastic strain caused by the displacement of mobile dislocations. Thus, the differences between the two TRIP steels studied are related to the microstructure and the different dislocation structures observed in them. A notable consequence of this study is a better accuracy in the prediction of springback passes due to a better understanding of these inelastic effects that stems from going beyond mere use of traditional Young's modulus values.

Reduction of CO2 Emissions from Integrated Steel Works and Its Subjects for a Future Study

Abstract: Reduction of CO2 emissions has been discussed using newly developed precise model based on carbon and energy balance in large-scale integrated steel works as a whole. Although there are various means to decrease reducing agent rate (RAR) at blast furnace, preferable way to reduce CO2 emissions must be chosen considering energy balance in whole steel works. Reduction of RAR at blast furnace together with energy saving at downstream processes is important. Maintaining competitiveness in global steel market must be also considered. Simple reduction of RAR such as improvement of shaft efficiency at blast furnace without energy saving at downstream processes leads to increase in production cost because of increment of purchased energy. Injection of waste plastics and carbon neutral materials such as biomass is better alternative.Regarding blast furnace operation, under the use of inferior raw materials such as low strength coke as well as high productivity condition, there are many problems to be solved to achieve low RAR operation. It has been reported that drastic change of lower part situation such as increase in coke degradation and accumulation of coke fine causes operation instability at actual blast furnace. Therefore, to attain stable low RAR operation, it is confirmed that new control measures based on fundamental researches to solve various problems should be developed.

Examination of Oxide Scales of Hot Rolled Steel Products

Abstract: Porosities in the scale layer and wavy scale-steel interfaces are two common artefacts generated during metallographic preparation of oxide scale samples. This paper presents the techniques used by the authors to effectively remove porosities in the scale and reduce the waviness of the scale-steel interface so that the true scale structures can be examined. The techniques have been successfully applied to the examination of oxide scales on hot-rolled steel with various thicknesses and structures.

Mathematical Heat Transfer Model Research for the Improvement of Continuous Casting Slab Temperature

Abstract: To improve the temperature of continuous casting slab, a mathematical heat transfer model simulating the solidification process of continuous casting slab was developed based on the technical conditions of the slab caster of Steelmaking plant of Wu-Han Iron and Steel Group Corp., by which the slab temperature distribution and shell thickness were computed. The adequacy of the model was compared with the measured slab surface temperature at the caster exit. The effects of the main operation parameters including casting speed, secondary cooling conditions, slab size and steel melt superheat on the solidification process were discussed and the means of enhancing the slab temperature was brought forward. Raising the casting speed from 1.0 or 1.1 to 1.3 m/min, controlling the flow rate of secondary cooling water and optimizing the spray pattern at the lower segments of secondary cooling zone could effectively improve the slab temperature. Whereas increasing the superheat is adverse to the production of slab with high temperature. The results of model research have been applied to plant operation at Steelmaking plant of Wu-Han Iron and Steel Group Corp. The slab surface temperature has risen from 900 to 1 250°C, and the slab are directly fed to the rolling mill after exiting caster.

Solid Inclusion Transfer at a Steel-Slag Interface with Focus on Tundish Conditions

Abstract: The separation of non-metallic inclusions from the steel to the slag phase in the ladle during secondary steel making operations and in the tundish and mold during casting is very crucial to the pr ...

High Power Ultrasonics in Pyrometallurgy: Current Status and Recent Development

Abstract: In recent years, a large number of studies have been published on the use of high intensity ultrasonics in various high temperature technologies. This paper provides an overview of the recent achievements and ongoing works on the application of high intensity sound waves to pyrometallurgy and its related areas. The published results have strongly suggested that ultrasonics has the potential to play a more significant role in such areas as the dedusting of high-temperature exhaust gas, improvement of fuel-combustion efficiency, control of air-pollutant emissions, improvement of the quality of ingots, production of metal powders and as-cast composite materials.At higher temperatures, special attractiveness of sound waves is associated with the fact that the waves can propagate through gas, liquids, and solids, and thus supply the acoustic energy from a cooled sonic generator to materials being processed under high temperature conditions. This provides a unique tool, for example, for controlling the rates of interfacial phenomena that is unachievable by any other methods under high temperatures.Industrial competitiveness of the ultrasonic-based technologies is reinforced by the relatively low cost of power-generating equipment and ultrasonic transducers. However, further research efforts are called for to develop new heat-resistant waveguide materials and to integrate the ultrasonic installations with existing industrial facilities in high temperature technologies.

Fabrication of Ultrafine Grained Ferrite/Martensite Dual Phase Steel by Severe Plastic Deformation

Abstract: Processing of ultrafine grained ferrite/martensite dual phase (UFG F/M DP) steel by equal channel angular pressing (ECAP) and subsequent intercritical annealing was described in detail. Along with strain gradient plasticity concept in which an introduction of a high density of geometrically necessary dislocations attributes to enhance strain hardenability, the aim of the present study was fabrication of UFG F/M DP steel exhibiting extensive strain hardenability, which other UFG materials hardly exhibit, in addition to ultrahigh strength and good uniform elongation. By selecting the optimum ECAP and intercritical annealing conditions, it was possible to fabricate UFG F/M DP steel in which isolated UFG martensite islands were uniformly embedded into UFG ferrite matrix. The formation of such a unique microstructure under the present processing conditions was discussed in terms of microstructural evolution during ECAP. Room temperature tensile properties of UFG F/M DP steel were superior to those of coarse grained counterpart. More importantly, in spite of an UFG structure, the present UFG F/M DP steel exhibited extensive strain hardenability from the onset of plastic deformation in association with grain size independent strain gradient plasticity, unlike other UFG materials.

Improvement of sinter softening property and reducibility by controlling chemical compositions

Abstract: Increasing permeability of packed materials in a blast furnace and decreasing reducing agent rate at a blast furnace process take an important role to improve productivity In order to increase permeability and decrease reducing agent rate, sinter softening property during reduction and sinter reducibility are importantEffects of sinter compositions (CaO, SiO2, Al2O3, MgO, FeO) on the sinter softening property during reduction and sinter reducibility were examined by samples produced from pot scale sintering These compositions were controlled by lime stone, serpentine, and coke breeze content and varying iron ore source in raw sinter materials And sinter softening property was estimated by vertical pressure drop of sinter packed bed (70 mmφ×100 mm) during sinter reduction with raising temperature to 1 600°C under vertical loading force (98×104 N/m2) This pressure drop is caused by melt formation from slag compositions in sinter above 1 000°C And sinter reducibility was estimated as reduction degree by CO(30%)-N2 gas under constant temperature conditions (900°C, 1 100°C)Results were obtained as follows(1) Low SiO2 and low CaO sinter had superiority of sinter softening property That is small pressure drop caused by decreasing SiO2-CaO-FeO melt(2) And low SiO2 and low CaO sinter had high reducibility at both 900°C and 1 100°C It is considered that decrease of these compositions affects restriction of calcium silicate containing ferrous oxides(3) High MgO and high FeO sinter using dolomite instead of serpentine and blended with high coke breeze also had superiority of sinter softening property Adding MgO to phase of CaO-FeO-SiO2 raises melting temperature The raising melting temperature is considered to make high pressure drop region to be narrow(4) And high MgO and high FeO sinter had low reduction degree at 900°C but kept high reduction degree at 1 100°C X-ray diffraction pattern for the sinter indicated that it contained much magnetite structure (magnetite and magnesioferrite) instead of hematite This mineral composition is consistent with low reduction degree at 900°C On the other hand, keeping high reduction degree at 1 100°C is considered to correspond not to promote silicate (FeO-2SiO2, FeO-SiO2-CaO) formation By X-ray micro analyzer, it was found that calcium ferrite contained more Si and more Mg ion with increasing MgO in sinter Increasing Si ion in calcium ferrite is considered to be the cause of restricting silicate formation(5) Al2O3 content has little effect to sinter softening propertySummarized these results, low SiO2, low CaO, high MgO and high FeO sinter has a good softening property and high reducibility These characteristics indicate good performance as raw material in a blast furnace

Vortexing flow patterns in a water model of slab continuous casting mold

Abstract: A water model experiment was conducted to observe the vortexing flow in the steel slab continuous casting mold, the snake- shaped Plexiglas mold was designed to simulate the actual caster. The camera was used to record the flow patterns, which were visualized by injecting the black sesames into water. The changes of shape of single vortex and two vortices with time have been observed during experiments. A numerical model has been developed to analyze the vortexing flow, which may be produced by moving the submerged entry nozzle from center to off-center in the slab continuous casting of steel. According to the numerical results, the vortexing flow is resulted from three-dimensional biased flow in the mold. A vortex is located at the low velocity side adjacent to the submerged entry nozzle. The vortex strength depends on the local horizontal velocity of fluid and decreases gradually with distance from the free surface. The vortexing zone size depends on the biased distance of the submerged entry nozzle, and intensity of the vortexing flow depends on the casting speed of the continuous caster.

A model for estimation of viscosity of molten silicate slag

Abstract: A model to evaluate the viscosity of silicate melts is proposed on the basis of the bonding states of oxygen, i.e. non-bridging oxygen and free oxygen ions, in the silicate structure, considering the flow mechanism of the melts with the network structure. Gaye's model is applied to evaluate the bonding state of oxygen ions using thermodynamic databases. The present model can reproduce the composition dependence of the viscosities for silicate melts in binary systems with a single model parameter, as well as the composition dependence of the viscosities for ternary systems in a wide composition range.

Comparison between standard and renormalization group k-ε models in numerical simulation of swirling flow tundish

Abstract: Because of the introduction of a cylindrical swirling chamber into a neotype tundish, the Swirling Flow Tundish (SFT), the numerical simulation becomes difficult for this kind of tundish by the standard two-equation k-e turbulence model. So another kind of k-e turbulence model, the Renormalization Group (RNG) k-e turbulence model derived from the theory of renormalization group, was adopted and compared with the standard one. Both of these two kinds of turbulence models were used to simulate the flow patterns in SFT on staggered grid systems based on Finite Volume Method (FVM) with SIMPLER algorithm for steady 3D and incompressible Newtonian turbulent flows. The comparison of simulation results from these two models shows that the RNG k-e turbulence model for SFT leads quicker convergence than the standard one. Unsymmetrical flow patterns were obtained and the grid independence of this mathematical model for SFT was also discussed. The theoretical analyses of forces on particle, turbulent kinetic energy distribution and lower flow velocity behind dam and weir show that there will be a good effect for non-metal inclusion aggregation and separation with the swirling chamber.

A Mathematical Model to Study Liquid Inclusion Behavior at the Steel-Slag Interface

Abstract: The separation of non-metallic inclusions at the interface between the steel and the slag in the ladle, tundish and mold is an essential part of the production of clean steel. It is therefore, of great importance to have a deep understanding of the phenomena controlling the transfer of inclusions from the steel to the slag layer. In this work a mathematical model, derived from the equation of particle motion, have been used to study the transfer of liquid inclusions to slags. The effects of the drag, added mass, buoyancy and rebound force on the inclusion transfer are considered. The model relies, to a great extent, on the availability of accurate information of the magnitude of a number of physical properties of the involved phases. Among those properties, the interfacial tension between the phases and the slag viscosity were found to be the most critical. Due to the fact that the availability of experimentally obtained high-temperature physical property data, relevant to the industrial conditions, is scarce in the literature several different model descriptions have been used in this work to estimate these properties. The mathematical model has been used to investigate the separation of liquid non-metallic inclusions, of different size and composition, to a number of different industrial ladle slag compositions.

A Perspective of Goethitic Ore Sintering Fundamentals

Abstract: The main purpose of iron ore sintering is to produce a strong agglomerate for the blast furnace. This is achieved by partially melting a sinter mix at high temperature and then allowing the melt to solidify into a bonding phase for the unreacted material. The melt formation and subsequent solidification processes are highly dependent on the composition of the blended mix. This paper summarises the differences in sintering behaviour between hematite ores and goethitic ores based on past research programs carried out at BHP Billiton. From a fundamental evaluation of the sintering process, it is clear that productivity can be an issue with goethitic ores because of their low bulk density and high porosity. This paper recommends steps towards overcoming losses in productivity. The effect of goethitic ores on coke rates is also a matter of general concern and this study shows that the addition energy required to dehydrate goethites and remove the additional water introduced into the system is comparatively small. The properties of melts have been shown to be particularly important in determining yield from a sinter machine and it is evident that the easy-melting properties of goethitic ores will also have an impact on this area. This paper also reviews our current understanding of how goethitic ores can influence sinter quality. The implication of fundamental knowledge on practical sinter plant operation is discussed throughout and collated at the end of the paper.

The Observation of Mold Flux Crystallization on Radiative Heat Transfer

Abstract: As an important factor in the moderation of heat transfer in continuous casting mold, mold flux has been researched widely However, the study of the effect of solid mold flux on radiative heat transfer has not been conducted widely By using an infrared radiation emitter, which was developed at Carnegie Mellon University, a radiative heat flux was applied to a copper mold to simulate the heat transfer phenomena in continuous casting The effect of adding a thin slag disc on top of copper mold on radiative heat transfer has been analyzed It was found that the presence of mold flux enhanced radiative heat transfer rate The effect of full crystallization of a slag disc was to reduce the heat transfer rate by 20% compared with a completely glassy sample The specific effect of full crystalline and glassy parts of the mold flux on radiative heat transfer, and the influence of their properties on heat transfer rate was discussed in this paper

Modelling of Microstructure Evolution during Hot Rolling of a 780 MPa High Strength Steel

Abstract: The microstructure evolution during thermo-mechanical processing of a state-of-the-art Ti-Nb HSLA steel with a tensile strength of 780 MPa has been investigated with laboratory investigations. The entire hot strip rolling process was simulated with hot torsion tests. Using the Gleeble 1500 thermomechanical simulator, constitutive behaviour, static recrystallization and austenite decompositon were quantified with single and double hit tests as well as continuous cooling transformation (CCT) tests. Precipitation strengthening was studied using aging tests. Based on the experimental results a microstructure model is proposed for hot rolling, run-out table cooling and coiling of the investigated steel. The model has been applied to predict the microstructure of industrially processed coils. The prediction of the ferrite grain size is seen to be in good agreement with that obtained during industrial hot strip rolling.

Hydrothermal synthesis of zeolite A using blast furnace slag

Abstract: Alkali hydrothermal synthesis of zeolite A using blast furnace (BF) slag was investigated. The preliminary experiment was conducted in use of synthetic slag consisting of SiO2, Al2O3, and CaO powders, and it was made clear that the most optimum slag compositions to synthesize zeolite A were the molar ratio of Si to Al (Si/Al) of 1 and reduction of CaO content down to 15 mass%, and that hydrothermal treating conditions were the temperature range from 328 to 358 K, NaOH solution of 1 M (=mol/L) and the ratio of the volume of NaOH solution to total mass of slag (Vsol/Wslag) of 15 (mL/g). It was also found that synthetic slag with such a higher content of CaO as 40 % resulted in formation of tobermorite and hydrogarnet. In the experiment using BF slag, zeolite A could be successfully synthesized by optimizing both conditions of the compositions of raw material powders and hydrothermal treatment as noted above, where optimization of the compositions of raw material powders such as Si or Al content were performed by the suitable amount of addition of SiO2 powder or NaAlO2 powder as a source of Si and Al. The ball milling type reaction vessel containing numerous small SiC balls which was first adopted in this hydrothermal treating study was confirmed to be very effective for acceleration of synthetic reaction rate, shortening markedly the time period needed for fully synthesis of zeolite A. Temperature dependence of heat capacity of zeolite A powder synthesized in use of BF slag was measured after absorption of vapor at the ambient temperature, showing endothermic behavior with the peak at the temperature of around 473 K.