Development and application of fluorine free mould fluxes have been widely studied in recent years. Some research has shown that B₂O₃ and TiO₂ are potential substitutes for F^– in mold fluxes. In this study, Structure of CaO–B₂O₃–SiO₂–TiO₂ glass system has been studied by Raman spectroscopy. The influence of basicities (CaO/SiO₂) and contents of B₂O₃ and TiO₂ on the structure of CaO–B₂O₃–SiO₂–TiO₂ glasses were examined. Experimental results indicate that TiO₂ exists in the system in the form of [TiO₄] as network former in range of 0–15% in mass. The degree of polymerization of this system decreases with increase of basicities. The increase of B₂O₃ leads to more [BO₄] tetrahedral units. It is concluded that both B₂O₃ and TiO₂ behave as network forming oxides within the studied system.

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The effect of the raw materials and mixing ratio on the heat transfer and structure of mould slag was studied in the present paper. Three groups of mould slag with identical chemical composition were designed by various raw materials and mixing ratio. The result indicates that the raw material has minor effect on viscosity, melting point and crystalline phase of the mould slag; whereas, it affects the formation and size of crystal. The wollastonite in slag has higher crystallization capacity; therefore, it promotes the formation of thicker solid slag film with higher porosities and consequently prevents the strong heat flux through the slag film. Compared with wollastonite, prefused material in the slag has capability to restrain the crystallization process; hence, the thinner solid slag film with uniform size and finer grain is formed. The experiment proves that prefused mould powder has good performance on heat transfer.

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A theoretical study is made on the maximum injection rates of pulverized coal in ironmaking blast furnaces. The study takes account of two restrictive conditions which enable stable blast furnace operations to be maintained. One is to burn out the injected coal in the raceway zone and the other is to avoid the coal ash deposition on the blowpipe wall. The predicted maximum injection rates for some operating blast furnaces are about 190–210 kg per ton of pig-iron produced, which seem to be reasonable in comparison with experiences reported. Also, the influences of pulverized coal injection on the coke consumption, the production rate of pig-iron and the bosh gas temperature are examined in relation to some blast gas conditions such as the oxygen enrichment and the moisture addition.

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Eight polyaromatic hydrocarbons that are model compounds of coal extract were added to coal blends to clarify the mechanism of the effects of coal extract (HyperCoal) on coke strength. Addition of large aromatic-ring compounds (coronene, perylene, naphtho[2,3-a]pyrene) greatly enhanced coke strength, whereas three-ring aromatics (anthracene, phenanthrene) had no significant effect on coke strength. Because large polyaromatic compounds have greater affinity for coal molecules, they co-fused with the coal particles. As a result, formation of large pores during coking was suppressed, leading to increased coke strength.

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Inter-particle percolation at the interfaces between burden layers directly influences the permeability of the burden in the shaft of the blast furnace. This paper studies inter-particle percolation of small particles (pellets) into large particles (coke) during the burden descent through small-scale experiments and simulations. A special device was designed for making it possible to consider the effect of the increase in cross-sectional area along with the burden descent. The simulations, which are based on the discrete element method, were first validated using one experimental case. An overall agreement was found between the experiments and the simulations. The velocity distribution of coke and pellet particles in the small bed, the trajectories along the height of the bed and the quantity of percolating particles at different heights of bed were investigated. The results show a considerable inter-particle percolation of pellets into the underlying coke layer at the wall area, but also a percolation over the whole radius of the system. These findings stress the importance of taking measures to prevent percolation by proper design of the charging programs in the operation of the blast furnace.

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Pelletization tests were conducted using pulverized iron ore to record changes in pellet strength by changing the volume of micro-particles and ore types. The strength of pellets when completely dried can be explained by the volume of micro-particles in ore, and the greater the volume of micro-particles, the higher the strength of pellets. The rate of increase in pellet strength by micro-particles when completely dried varies depending on the ore type of micro-particles and the strength increases in the order of pisolite, Marramamba, and hematite. Regarding the generation of pellet strength during the moisture drying process, there are two different mechanisms at work at the early stage and the last stage before complete dryness. The rise in strength at the early stage of drying is considered attributable to the increase in liquid viscosity due to the condensation of micro-particles and APD in the liquid, and the increase in strength just before complete dryness is considered attributable to the formation of solid bridges caused by the movement and rearrangement of micro-particles.

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The current issues of sintering technology in the iron and steel making industry are how to increase productivity of sintering process and to maintain proper quality of sintered ore. In the conventional sintering bed, combustion of solid fuel supplies heat required for sintering while it generates imbalance of heat concentration in the bed. The unevenly distributed heat is considered to be problematic on the quality aspect of sintered ore. Therefore, in order to maximize the production rate and quality of the products, an investigation for improved operational mode is indispensable. In this study, the effect of additional oxygen supply with an adjustment of injection location is discussed. Scale downed pot tests in addition to computation by previously developed unsteady 1-dimensional sintering bed model are employed for the examination. Also, quantitative parameters are applied to evaluate the changes of sintering process and the combustion characteristics are systemically analyzed among designed cases. The reactivity of coke combustion tends to increase with the enrichment of oxygen in the induced air. However, the degree of change in the sintering time as well as effective heat supply varies according to the locations of oxygen injection.

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This paper presents an initial part of a project devoted to the recycling of mill scale in the form of self-reducing briquettes. First chemical and morphological characteristics of mill scale were investigated and next its gaseous reduction behavior was studied by thermogravimetry. The chemical characterization showed that wustite is the major constituent of this waste matter, with small amounts of magnetite, hematite and metallic iron. The microscopic examination of the scale revealed its complex and layered microstructure with three distinct zones. The outer layer is relatively thin and porous. It is mainly composed of hematite and magnetite. The intermediate layer is made of the dense, columnar grains of wustite. The inner layer is a very porous wustite. The gaseous reduction by carbon monoxide has a topochemical character regardless of initial morphology of scale and, depending on temperature and reducing gas composition it produces a porous iron or the iron whiskers. The unreacted shrinking core model with one interface fits quite well the kinetic data and the activation energy of reduction is about 80 kJ/mol.

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Researches on top lance gas injection in a cylindrical bath are carried out based on water model experiments. The penetration depth of bubbles and a swirl motion are investigated because of their practical importance. Empirical equations are proposed for the penetration depth as a function of a modified Froude number. A bath surface oscillation map is drawn in order to identify the occurrence condition of the swirl motion, and then empirical equations are proposed for describing the occurrence condition of the swirl motion. The characteristics of the swirl motion are also analyzed, and empirical equations are proposed to predict starting time, period, amplitude, and damping time of the swirl motion.

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A comprehensive model of oxygen steelmaking that includes the kinetics of scrap melting, flux dissolution, slag chemistry, temperature profile of the system, formation and residence of metal droplets in the emulsion, and kinetics of decarburization reaction in different reaction zones was developed. This paper discussed the development and the application of the model into an industrial practice. The results from the model were consistent with the plant data from the study of Cicutti et al. The model suggested that 45% of the total carbon was removed via emulsified metal droplets and the remaining was removed from the impact zone during the entire blow. It was found that the residence time of droplets as well as decarburization reaction rate via emulsified droplets was a strong function of bloating behavior of the droplets. This model is the first attempt in the open literature that allows for the decarburization kinetics of the impact zone to be predicted separately from decarburization kinetics of the emulsion.

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The development of a global model for oxygen steelmaking and its validation against industrial data was reported in Part 1 of this paper. This paper focused on the development of one sub-model on the decarburization reaction in the emulsion zone incorporating the bloated droplet theory. This paper also critically evaluated the current knowledge on the kinetics of decarburization reaction in the emulsion phase and discussed the repercussions of the new model for industrial practices. The decarburization model, in conjunction with the industrial data, indicates that the decarburization rates in the emulsion phase reaches up to approximately 60% of the overall decarburization rate during the main blow. It was found that the residence time of droplets as well as decarburization reaction rate via emulsified droplets was strong function of bloating behavior of metal droplets in the emulsion phase. The estimated residence times of the metal droplets in the emulsion were between 0.4 to 45 s throughout the blow. The influence of variations in droplet size and ejection angle on residence time and decarburization rates via emulsified droplets was also investigated. It was shown in this study that the decarburization rates in the emulsion were accelerated if droplet size was decreased or if the ejection angle was decreased.

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The development of a global model for oxygen steelmaking and its validation against industrial data has been reported in Part 1 of this paper. Part 2 of this paper explained the model development of decarburization reaction of emulsified droplets and discussed the effects of bloating behaviour of metal droplets on the overall kinetics of the process. Part 3 of this paper focussed on the development of one sub-model on the decarburization reaction in the impact zone and critically evaluates the important process variables affecting the decarburization kinetics. Decarburization rates in the impact zone were calculated using the semi-empirical relationships developed from experimental results. Based on previous experimental studies, both diffusion through the gas phase and surface control were considered in the rate calculations. The model was validated against experimental data from Belton and Sain, and against plant data from Cicutti et al. The model developed was consistent with the experimental and plant data, and provided a reasonable basis for predicting the decarburization of iron in the impact region of oxygen steelmaking. The model predicted that the decarburization rate is sensitive to the partial pressure of carbon dioxide and oxygen in the impact zone. As the partial pressure of oxygen decreased from 26.4 to 16.2 kPa, the model predicted that that the reaction rate of decarburization via oxygen decreased from 202 to 134 kg/min. The model predicted that approx. 40% of decarburization takes place in the impact zone during the main blow.

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Gas injection in metallurgical vessels is an important tool to improve chemical and thermal mixing. Chemical mixing has been extensively studied in the past 40 years, however, thermal mixing is still poorly understood. This work reports a mathematical model developed to describe the effect of the number and position of porous plugs on thermal and chemical mixing under industrial conditions.
A relevant contribution of this work is the evidence indicating a suppressing effect of bottom gas injection on thermal homogenization with off-center gas injection; furthermore, it also suggests that mixing time is optimized with only one nozzle instead of two or three.

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Experiments have been conducted on oxygen gas entrainment by argon gas jets and molten steel oxidation with argon-oxygen gas mixture blowing. Oxygen entrainment behavior of gas jets and gas-phase mass transfer with gas blowing have been evaluated. Reaction rate models for molten steel oxidation with argon gas blowing in oxidizing atmosphere have been presented. The oxidation rates of molten steel with argon gas blowing on the molten steel surface in oxidizing atmosphere and plasma heating in the tundish have been measured and the results have been analyzed from the viewpoints of kinetics. Both oxidation rates have been explained by reaction rate models considering oxygen entrainment by gas jets and gas-phase mass transfer with gas blowing.

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Based on the experiments of laser welding of ultra-high strength steel (UHSS), joint morphology, microstructure, hardness and tensile-shear properties are investigated. The results show that the defects such as gas holes and cracks do not appear in the weld metal if the optimized parameters are employed. Microstructures of the weld metal and HAZ are mainly martensite, the widths of martensite lath aren't sensitive to the welding speed. However, the welding speed affects the grain sizes of prior autensite of the weld metal. When changing the welding speed from 20 mm/s to 35 mm/s, the mean widths of prior austenite grains decrease from 10.67 μm to 7.68 μm. In the HAZ, the hardness decreases apparently for the soft ferrite appears. The test results also show that the joint tensile-shear strength can satisfy the demand of production. Consequently, the laser welding quality of UHSS is reliable for manufacturing.

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High strength steels Q690+Q550 were welded using three different welding wires without preheating by gas shielded arc welding process. Microstructural characteristics of weld metals and nucleation mechanism of acicular ferrite were investigated by means of scanning electron microscope (SEM), energy dispersive spectrum (EDS) and transmission electron microscope (TEM). The straight Y-groove test and impact test were employed to assess cracking resistance and impact toughness of joints. Results indicated that the addition of Ti and Cr in the MK·G60-1 weld metal suppressed the formation of pro-eutectoid ferrite and ferrite side plate and contributed to the formation of acicular ferrite. The inclusions composed of (Ti, Mn) oxides and Mn, Cu sulfides became nucleation sites of primary acicular ferrite. Secondary acicular ferrites were nucleated on some pre-existing ferrite laths. Impact toughness and cracking resistance were enhanced with the increase of acicular ferrite in the weld metal.

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The methodologies of controlling the surface texture of die by hybrid (double)-shot treatment and nitiding at a low temperature were examined for the development of long life cycle die applied to the high strength steel sheets. Hybrid-shot improved the galling property because of its lubricating effect, while nitriding at low temperature which is useful for decreasing distortion by heat-treatment had sufficient hardness of 1500 HV for anti-abrasion. Surface texture of die material, evaluated by using Fast Fourier Transformation (FFT) analysis revealed that the ratio of the spectrum amplitude between high and low frequencies was corresponding to the galling generation load.

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Microstructures of chip specimens of high-strength materials produced by machining were examined by FE-SEM/EBSP method (an orientation imaging microscopy, OIM). In the ferritic SUS430 (16Cr) steel, the chip specimen with shear strain (γ) of ~7.5 was principally composed of equiaxed submicron grains which were for the most part surrounded by large angle grain boundaries (misorientation, θ≥15°). A similar microstructure was observed in the chip specimen with γ ≈ 22 of the Inconel X-750 (NCF 750) nickel-base alloy. However, the chip specimen of the austenitic SUS304 (18Cr–8Ni) steel (γ ≈ 14) and that of the 6061-T6 (aluminum) alloy (γ ≈ 10) exhibited principally a deformed microstructure with elongated grains and sub grains separated by small angle (2°≤θ<5°) or medium angle grain boundaries (5°≤θ<15°), although equiaxed submicron grains were partly observed. The chip specimens exhibited very high hardness compared to the original materials except 6061-T6 alloy. The maximum hardness value (609 Hv) was observed in the chip specimen with γ ≈ 22 of the Inconel X-750 alloy. Strong particles with equiaxed submicron grain structure, which can be easily produced by milling of cutting chips of commercial alloys, will be potential strengthener for metal matrix composites.

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The microstructure and toughness in Fe–0.04%C–1.85%Mn–0.03%Si–0.018%Nb steel deoxidized with Ti and Zr have been studied as functions of particle characteristics, austenite grain size and soluble Ti and Zr contents using a simulated HAZ (heat affected zone) thermal cycle (peak temperature, 1400°C; peak holding time, 60 s; time of cooling from 800 to 500°C, 70 s) and submerged arc welding (heat input of 15 kJ/mm), respectively. Microstructures were studied in samples containing 1.0 to 1.5 μm-diameter oxide particles numbering 500 to 2000 mm^–2 and with a soluble oxygen content of 10 to 30 ppm (measured before casting) and soluble Ti and Zr contents of 50–150 ppm. The γ grain size after HAZ thermal cycle in the range between 200 and 600 μm is controlled by pinning and solute drag. Small γ grain size below 300 μm was obtained with high soluble Ti and Zr contents of 110–160 ppm, whereas large γ grain size above 300 μm was obtained with low soluble Ti and Zr contents of 60–110 ppm. Two types of microstructures that showed high Charpy absorbed energy (VE(–10°C)= 150–250 J and VE(–50°C)= 50–150 J) were observed independent of γ grain size: One is acicular ferrite and a small amount of grain boundary ferrite (GBF) and ferrite side plate (FSP) and the other is GBF, FSP and granular bainitic ferrite. It was observed that low VE(T) values are attributed to the formation of porosity, large-size particles, carbides (+nitrides) and lathe bainitic ferrite.

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It is very important to know the morphology and chemical properties of subscales of oxide layers on surface for controlling and understanding high temperature oxidation in electrical steel. In present work, the oxide layers were investigated by various methods of transmission electron microscopy (TEM) such as scanning transmission electron microscopy (STEM), nanobeam electron diffraction (NBD), energy dispersive X-ray spectrometry (EDS), and electron energy loss spectrometry (EELS). The high-angle annular dark field (HAADF) of STEM could be a useful analysis technique to study the morphology of the oxide layers. The main oxides formed in the subscales during the decarburization annealing were fayalite, iron oxides, and silica, which were identified by EDS, NBD and EELS. The crystalline fayalites were found both in the surface region within several tens nanometers and in the region within a micrometer surrounding silica, and the atomic configuration in the unit cell of the fayalite was presented. Amorphous silica was formed both in the upper region of the subscales with a spherical shape and in the interface between the spherical silica and the iron matrix with a lamellar shape. TEM could be useful technique to characterize morphologies, microstructures and elemental compositions of oxides, and to understand the oxidation mechanism for the manufacture of the high quality electrical steel.

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The effect of phosphorus on the Hall-Petch coefficient (k_y) of polycrystalline ferritic steel was investigated by using interstitial free steel (IF steel) and an ultralow carbon (60 ppm C) steel containing different amount of phosphorus. The k_y of IF steel was around 100 MPa·μm^1/2 regardless of the amount of phosphorus. On the other hand, the k_y of ultralow carbon steel containing phosphorus was higher than that of the IF steels, but significantly lower than that of the ultralow carbon steel without phosphorus. The analysis by Auger electron spectroscopy revealed that carbon segregates at ferrite grain boundary, and the amount of segregated carbon tended to be reduced by the addition of phosphorus. From these results, it can be concluded that phosphorus does not directly influence the k_y of polycrystalline ferritic iron, but indirectly decreases the k_y by reducing the amount of carbon segregated at grain boundary.

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By using a reconstruction program recently developed by the present authors, the parent austenite grain structure is reconstructed from the crystal orientation map of bainite structure. Local austenite orientation can be reconstructed from non-ausformed bainite structure with errors of 1.7° and 1.0° at spatial resolutions of 5 and 20 μm respectively. The angle of errors is further reduced to be less than 0.5° when an analysis area is extended to a whole austenite grain. Application of the reconstruction program to the bainite structure transformed from deformed austenite has clarified that the variation in grain shape and deformation texture of parent austenite can be well reconstructed.

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Blast furnace (BF) slag, one of the byproducts of iron- and steel-making plants, was converted into a hydrocalumite-like compound using the alkali fusion method. The slag was transformed into the precursor with reactive phases via alkali fusion, after which the precursor was added to distilled water and stirred at room temperature to synthesize the product including a hydrocalumite-like compound. The effects of the mixed ratio of NaOH to the slag (NaOH/slag ratio), fusion temperature, ratio of precursor mass to distilled water volume (W/V ratio) and crystallization reaction time on the product phase were investigated, and the removal abilities of the obtained product for certain ions from aqueous solution was examined. Optimal conditions for hydrocalumite synthesis are a NaOH/slag ratio of 1.6, fusion temperature of 600°C, W/V ratio of 125 g/L and reaction time of more than 24 h. The product could remove more NH₄⁺, Sr²⁺, F^–, PO₄^3– and AsO₄^3– than BF slag, while the removal of Cl^–, SO₄^2– and NO₃^– was almost zero. These results suggest that a hydrocalumite-like adsorbent able to remove pollutant ions in aqueous solution can be synthesized from BF slag via alkali fusion.

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With a sharp increase in demand and production, palm oil wastes, (i.e. empty fruit bunches, fibre and shells) are generated, out of which a large amount ends up in landfill. In such a context, alternative solutions are needed to reduce the impact of these agricultural wastes on the environment. The present paper investigates the effect of addition of agricultural waste materials on the combustion behavior of its blends with metallurgical coke (MC). Two types of agricultural waste materials, palm shell and coconut shell, were mixed in different proportion with MC, while the gas phase reactions were studied at 1200°C in a drop tube furnace (DTF). In the tested conditions, the blends containing agricultural waste materials indicated higher combustion efficiencies compared to MC alone. Carbon structure analysis were performed through ¹³CP/MAS NMR spectroscopy showing various groups of carbons present in the agricultural waste samples ranging from aliphatic to aromatic carbons. The morphology of the samples was studied through Scanning Electron Microscope (SEM). SEM provided a qualitative description of the pore structure in the raw samples as well as the changes occurring following the gas phase reactions in the DTF. It was found that the particles derived from the wastes became increasingly deformed and lost their cell lumen. Surface area measurements were found to be in good agreement with the SEM images, supporting the higher combustion efficiency of the blends in comparison to coke alone. The present study suggests that agricultural waste materials have the potential to partially replace MC, as an auxiliary fuel in metallurgical processes.

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