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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 32 (1992), No. 1

  • The Background of the Special Issue on Interfacial Phenomena in Refining and Casting Processes of Iron and Steel

    pp. 1-2

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    DOI:10.2355/isijinternational.32.1

    x

    Readers Who Read This Article Also Read

    1. Swelling Phenomena of Molten Pig Iron Containing Titanium ISIJ International Vol.32(1992), No.1
    2. The Management of Research and Technology in the German Steel Industry with Respect to the European Union ISIJ International Vol.38(1998), No.9
    3. The δ to γ Transition in Fe-Cr-Ni Alloys during Laser Treatment ISIJ International Vol.37(1997), No.7
  • Current Views on the Structural Study of Interface of Liquids and Surface Layer of Solids

    pp. 3-10

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    DOI:10.2355/isijinternational.32.3

    Various phenomena of metallurgical interest are well-known to occur through the liquid-vapor and/or liquid-solid interfaces. Thus, a knowledge of the structure of interface of liquids and surface layers of solids is essential for profound understanding of these subjects. An attempt will be made in this paper to review some current information on the structure of liquid-vapor and solid-liquid interfaces, and a surface layer of solid determined from X-ray reflectivity measurements, grazing incidence X-ray scattering, and conventional and anomalous X-ray scattering measurements for fine particles with a crystalline size of about 10 nm or less. Some theoretical studies relating with these interfaces are also included for further convenience.
  • Interfacial Properties of Liquid Iron Alloys and Liquid Slags Relating to Iron- and Steel-making Processes

    pp. 11-18

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    DOI:10.2355/isijinternational.32.11

    Interfacial properties and adsorption behavior play an important role in the progress of heterogeneous reactions, so accurate values of these properties are required as the basic knowldge to examine the interfacial phenomena in iron- and steel-making processes. In this review, data for surface tension of liquid iron alloys and liquid slags, contact angle between solid and liquid phases, and interfacial tension between liquid and liquid phases, are briefly summarized on the basis of currently published articles.
  • Wetting and Marangoni Effect in Iron and Steelmaking Processes

    pp. 19-25

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    DOI:10.2355/isijinternational.32.19

    This article reviews the phenomena by which wetting and the Marangoni effect participate or may participate in iron and steelmaking processes. The concept of wetting conventionally defined for the system of gas-liquid-solid was applied to the systems of liquid 1-liquid 2-solid, liquid-solid 1-solid 2 and gas-liquid 1-liquid 2. In these systems, local corrosions of refractories at the interfaces of gas-slag and metal-slag, slag foaming, bubble dispersion into metal phase, and interaction of inclusions with solidification fronts were described in relation to the wetting and the Marangoni effect. Rates of reactions of gas-metal, and metal-slag were briefly introduced as examples of possible participation of the Marangoni effect.
  • Computer Aided Interfacial Measurements

    pp. 26-35

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    DOI:10.2355/isijinternational.32.26

    The sessile drop profile method was combined with X-ray radiography to develop a precise method to measure interfacial tensions and contact angles of liquid metals at high temperatures and in a variety of atmospheres. An accurate method of digital image processing was developed to capture, enhance and determine the coordinates of the X-ray shadow image of the droplet. Laplace's equation was then solved numerically to allow a non-subjective determination of interfacial tension and contact angles.
    Examples of the determination of the interfacial tension of mercury in argon, of liquid iron at 1 550°C under various CO/CO2 gas mixtures, of iron carbon alloys and of liquid iron in contact with a lime-alumina-silica slag at 1 550°C, are given.
  • Current Efficiency and Mechanisms of Redox Reaction of Iron at the Interface between Solid Iron and Molten Slags

    pp. 36-42

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    DOI:10.2355/isijinternational.32.36

    The electrode of solid Fe/40CaO-40SiO2-20Al2O3 (mass%) molten slag with 0.55-10 mass% of total iron oxide were electrolyzed in Ar at 1 573 K, using Pt-air/ZrO2-9mol%MgO electrode as a reference electrode. The current efficiency of the reaction of Fe=Fe2++2e was 1.0 for anodic overvoltage less than 200 mV and gradually decreased to 0.67 at 600 mV. The efficiency was zero for cathodic overvoltage until –600 mV. From the electrochemical analysis of the redox reaction of iron, it was concluded that the anodic reaction was the oxidation of iron to Fe2+ up to 200 mV and was accompanied by the oxidation of Fe2+ to Fe3+ above 200 mV. The cathodic reaction was the reduction of oxygen dissolved in molten slag.
  • A.C. Impedance Analysis of the Kinetics of Reactions between Molten Cu or Fe and CaO-Al2O3 Slag

    pp. 43-49

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    DOI:10.2355/isijinternational.32.43

    A chemical reaction at the interface between slag and metal can be analyzed as a kind of electrode reaction because of the ionic nature of liquid slag.
    In the present work, application of an A.C. impedance method to slag-metal reaction in iron- and steel-making process was tried to clarify the individual kinetic factors concerning the electrode reactions at the interface between slag and metal. The total impedance between CaO-Al2O3 slag and Cu-S or Fe-C-S melts was measured in this paper.
    The results obtained were successfully used to determine the individual factors on kinetics of the electrode reaction between slag and metal, such as solution resistance of slag, interfacial capacitance in electric double-layer, overvoltage of charge transfer, rate constant and so on.
  • Observations of Physical Phenomena Occurring during Passage of Bubbles through Liquid/Liquid Interfaces

    pp. 50-56

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    DOI:10.2355/isijinternational.32.50

    The physical phenomena occurring during passage of bubbles through liquid/liquid interfaces have been investigated with high-speed photography. Several combinations of liquid/liquid systems were used which can be divided into those with large and with small interfacial energy and density difference. Several examples of photo series are given. A summary of the various events can be documented by history diagrams. In all the systems material of the lower phase is carried into the upper phase. The photo series can be used to obtain quantitative data for residence time, film thickness, length of jet, interfacial area, droplet number, droplet size and others.
  • Characteristics of Entrainment at Liquid/Liquid Interfaces due to Rising Bubbles

    pp. 57-65

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    DOI:10.2355/isijinternational.32.57

    The entrainment phenomena occurring at liquid/liquid interfaces during passage of single bubbles have been investigated using the systems water/cyclohexane, mercury/water, and mercury/silicon oil. Measurements were performed on the increase of the continuous interfacial area, the residence time of the bubble at the interface, the length of the liquid jet of the lower phase drawn upwards, the number and size of droplets of the lower phase in the upper phase, the residence time of the droplets and their velocity of fall. Dimensionless correlations were derived for some of these quantities, and some consideration is given of the application of the data in mass transfer models.
  • Behaviour of Bubbles at Gas Blowing into Liquid Wood's Metal

    pp. 66-75

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    DOI:10.2355/isijinternational.32.66

    Experimental studies on the bubble behaviour in submerged gas blowing were carried out with liquid Wood's metal. About 440 kg of Wood's metal at 100°C was contained in a ladle-shaped glass vessel with an inner diameter of 40 cm. The liquid metal was stirred by nitrogen, argon or helium respectively through a nozzle positioned centrically or eccentrically at the bottom. The bubble plumes were investigated under different gas flow rates and nozzle diameters by determination of local gas fraction, bubble frequency, size distribution and rising velocity of bubbles.
    The measurements show that the radial distribution of gas fraction and bubble frequency can be described by a Gaussian function and the bubble size distribution obeys a log-normal function. Except for the region near the nozzle the mean rising velocity of bubbles is nearly constant over the radius. The influence of blowing conditions on these variables was estimated.
  • Swelling Phenomena of Molten Pig Iron Containing Titanium

    pp. 76-80

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    DOI:10.2355/isijinternational.32.76

    The phenomenon that molten pig iron containing titanium swelled and drooped when heated in levitation melting was observed. To clarify the mechanism of the phenomena, various iron containing carbon, titanium and nitrogen was melted under argon or nitorgen.
    Swelling phenomenon is caused by nitrogen gas evolved by decomposition of titanium compound in molten iron. Drooping phenomenon is caused by decrease in surface tension of molten iron by rapid nitrogen absorption. These phenomena were considered to relate with various troubles in blast furnace operation occurred at a heavy charge of titania-contained ore.
  • Slag-foaming Phenomenon in Pyrometallurgical Processes

    pp. 81-86

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    DOI:10.2355/isijinternational.32.81

    The slag-foaming phenomenon is observed in many pyrometallurgical processes such as basic oxygen steelmaking, pretreatment of molten pig iron and bath smelting of iron or chrome ore. The current state of understanding of this phenomenon is reviewed and particular attention is paid to its surface chemical view.
  • Slag Foaming in Smelting Reduction and Its Control with Carbonaceous Materials

    pp. 87-94

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    DOI:10.2355/isijinternational.32.87

    In the smelting reduction process of the thick slag layer type, it is important to keep slag height stably without abnormal slag foaming. This study investigated the mechanism of slag foaming control with carbonaceous materials by experiments using a 1-ton smelting reduction furnace and by X-ray fluoroscopic observation of phenomena occurring in a small graphite crucible. As the carbonaceous material was not wettable with slag, small bubbles coalesced on its surface. Because the large bubbles due to the coalescence of small bubbles rise through the foaming slag layer at a relatively high speed, the foaming of slag may be restrained. It was found that the smaller the size of the carbonaceous material was, the more effective was the carbonaceous material in controlling the foaming of slag. A certain extent of relative motion between carbonaceous material and slag was necessary to promote the coalescence of small bubbles. It was experimentally confirmed that the smelting reduction in 100-ton scale furnace can stably operate under the condition that the carbonaceous material is present in a sufficient amount in the slag.
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    1. Machanism of Iron Oxide Reduction and Heat Transfer in the Smelting Reduction Process with a Thick Layer of Slag ISIJ International Vol.32(1992), No.1
    2. Kinetic Analysis of Iron Carburizaiton during Smelting Reduciton ISIJ International Vol.44(2004), No.12
  • Machanism of Iron Oxide Reduction and Heat Transfer in the Smelting Reduction Process with a Thick Layer of Slag

    pp. 95-101

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    DOI:10.2355/isijinternational.32.95

    It is possible to stably operate the smelting reduction process of iron oxide with a thick layer of slag by controlling slag foaming with carbonaceous materials. In the present paper, the iron oxide reduction and the heat transfer in this process is investigated.
    (1) The overall rate constant of reduction, post combustion, heat efficiency and the state of the slag layer (temperature gradient and distribution of metal droplets) were measured by 5 t and 100 t scale experiments.
    (2) The amounts of reduction occurring at slag-metal bath, slag-metal droplets and slag-carbonaceous materials interfaces were estimated for the process under various conditions. Though the reduction at slag-metal bath inferface is predominant in a small furnace, the amounts of reduction at each site are almost equal in a 100 t experiment.
    (3) Heat transfer by radiation and gas convection was calculated by using a mathematical model and was compared with actual data. This model was constructed by dividing the furnace into three regions depending on the modes of reaction and heat transfer and by taking the mass and heat balances throughout each region. When the gas temperature is as high as 2170°C, the actual heat transfer can be explained mainly by radiation. But, under practical conditions (gas temperature ≤ 1765°C), the contribution of radiation and gas convection on heat transfer is only 20-30%. Therefore, heat transfer by circulation of super-heated carbonaceous material was assumed. The assumption coincides with the dependence of apparent activation energy of reduction on an experimental scale.
    (4) The appropriate condition for operating the smelting reduction process with a thick layer of slag is the combination of a sufficient amount of carbonaceous material and moderate intensity of stirring.
  • Post Combustion Behavior in In-bath Type Smelting Reduction Furnace

    pp. 102-110

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    DOI:10.2355/isijinternational.32.102

    In order to make a research on a new smelting reduction process, the iron bath based Smelting Reduction Furnace (SRF) with 5-ton iron bath capacity was installed in 1986 at NKK's Fukuyama Works and these test facilities were stepwisely built up.
    In this paper, post combustion behavior in the SRF is described, based on the integrated operations with the SRF directly connected to the Pre-reduction Furnace (PRF).
    Essential conditions to achieve high post combustion coupled with high heat transfer efficiency are summarized as follows;
    1) Height adjustment of a top blowing lance according to the change of slag surface level, permitting post combustion within slag which is considered to be a major heat transfer medium,
    2) Intensive agitation of slag phase by bottom blowing of gas,
    3) Ultra soft blowing of oxygen through a double flow lance, and
    4) Pressurized operation in which the depression of carry-over of charged coal is attainable.
    Under these conditions, longterm continuous operations over 10 h were stably carried out at high level of post combustion of 50% with heat transfer efficiency of more than 85% even in the use of high volatile coals.
    In the tests using various carbonaceous materials such as coke, medium volatile coal and high volatile coals, effects of volatile matter on post combustion were investigated.
    Furthermore, modelling of post combustion was studied to optimize the operating conditions in a larger scale furnace.
    x

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  • Rates of Nitrogen and Carbon Removal from Liquid Iron in Low Content Region under Reduced Pressures

    pp. 111-119

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    DOI:10.2355/isijinternational.32.111

    The kinetics of nitrogen and carbon removal from a liquid iron surface in low content regions by blowing Ar gas mixture under reduced pressures have been studied using the same vacuum induction furnace at 1 600°C, respectively. The results obtained are as follows:
    (1) The nitrogen removal reaction is described as a second order reaction with respect to nitrogen content. The overall reaction rate constant, kovN, decreases with the increase of total pressure, and oxygen and sulfur content.
    Assuming that the nitrogen removal reaction progresses by a mixed control and that the chemical reaction for nitrogen gas formation is caused by adsorbed nitrogen atoms, the chemical reaction rate constant, krN, and the adsorption coefficient of oxygen, κO, and of sulfur, κS, are estimated as follows:
    N+N=N2+_??_
    krN(=k[N]/fN2) cm/mass%/sec = 15/(1+κO·aOS·aS)2,
    κO=161, κS=63.4
    In the Fe-20mass%Cr-0.2Mass%C-S system also, the value of krN can be expressed by the same equation. It is thus concluded that, macroscopically, the mechanism of nitrogen removal is the same irrespective of whether or not the melt contains chromium.
    (2) In the carbon content range below 200 ppm, the overall carbon removal reaction rate constant, kovC, exhibits a maximum value against oxygen content, and decreases with the increase of sulfur content.
    Assuming that the chemical reaction for CO gas formation caused by the adsorbed carbon and the adsorbed oxygen atoms as a following equation, the dependence of the chemical reaction rate constant on oxygen and sulfur content is explained by the values of the adsorption coefficients κO and κS, respectively.
    C+O=CO+_??_
    The value of κO is equal to about 100-300 and that of κS is equal to about 40-65.
    These values are in general accord with those determined from the nitrogen desorption reaction.
    x

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    1. Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser ISIJ International Vol.32(1992), No.1
    2. Acceleration of Decarburization in RH Vacuum Degassing Process ISIJ International Vol.32(1992), No.1
  • Acceleration of Decarburization in RH Vacuum Degassing Process

    pp. 120-125

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    DOI:10.2355/isijinternational.32.120

    Fundamental experiments were carried out in order to accelerate the vacuum decarburization rate in low carbon range. As the results, it became clear that enlargement of interfacial area was more efficient than increase in overall mass transfer coefficient. One of the most practical methods to enlarge interfacial area was Ar injection into molten steel. Effect of Ar injection on decarburization rate was investigated in the 150 kg VIF. Ar injection was effective on decarburization rate, and the apparent decarburization rate constant with a two-holed nozzle was larger than that with a one-holed nozzle. Next, effect of Ar injection into a vacuum vessel of RH was investigated with a water model. CO2 desorption rate was measured to simulate decarburization rate. Gas injection nozzles were settled at the lowest part of the side wall in the vacuum vessel. The number of nozzles was 1, 8, or 16. An experiment without gas injection was also carried out as a reference. Gas injection into the vacuum vessel was effective on the CO2 desorption rate. In particular, increase in the number of nozzles was more effective at a constant total gas flow rate.
    Finally, plant trials were carried out. Configuration of the nozzles was the same as the case of 8 nozzles in the water model. Gas flow rate into the snorkel for circulation was 2 500 NI/min. Gas flow rate into the vacuum vessel was 800 NImin. Inner diameter of the nozzles was 2 mmφ. As the result, it became possible to decrease the carbon content from 200 to 10 ppm within 10 min.
    Interfacial area with Ar injection was evaluated to be 1.6 times larger than that without Ar injection.
  • Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser

    pp. 126-135

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    DOI:10.2355/isijinternational.32.126

    On the basis of a mixed-control mechanism involving the mass transfer of carbon and oxygen in the molten steel in the vacuum vessel and the transport of carbon and oxygen by the circulation flow, a new reaction model for RH decarburization has been developed to clarify the effect of oxygen concentration on the decarburization rate. The model can also predict the effect of the KTB method, in which oxygen gas is blown onto the molten steel in the vacuum vessel, on the decarburization rate.
    A significant dependence of the decarburization rate in the RH experiments on the oxygen concentration in the ladle, OL, has been found in the range of the carbon concentration in the ladle, CL, of more than 200 ppm. In the range CL200 ppm, the decarburization rate is apparently proportional to the carbon concentration, hence its dependence on OL is small. The model analysis predicts the dependence of the decarburization rate on OL, however, there is some difference between the calculated decarburization rate and the observed rate. This is presumed to be caused by an unidentified supply of oxygen to the molten steel in the vacuum vessel, which may result from the slag being drawn into the vacuum vessel and the leakage of atmospheric air.
    Volumentric coefficients of the mass transfer of carbon in the vacuum vessel of the RH, akC, was also investigated in the ultra low carbon range of less than 50 ppm using recent data, and was shown to have a strong dependence on the carbon concentration and the circulating flow rate, Q..
    x

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    1. Acceleration of Decarburization in RH Vacuum Degassing Process ISIJ International Vol.32(1992), No.1
    2. Mechanism of Decarburization in RH Degasser ISIJ International Vol.35(1995), No.12
    3. Development of Refining Process for Production of High Purity Ultra-low-carbon Steel Tetsu-to-Hagané Vol.76(1990), No.11
  • Denitrogenization Mechanism from Molten Steel by Flux Treatment

    pp. 136-141

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    DOI:10.2355/isijinternational.32.136

    Experiments of nitrogen desorption from molten steel by flux treatment have been proceeding and the reaction rates have been investigated. The flux of the CaO-Al2O3-CaF2-BaF2-SiO2-MgO system is effective for nitrogen desorption from molten steel, The nitrogen transfer rate from the steel to the gas phase could be increased by using the present flux, when the free surface of molten steel is exposed to argon atmosphere. The reason for the increase is that surface activity elements such as oxygen and sulphur in the molten steel were decreased and the interfacial resistance between the metal and gas was reduced. Under the present conditions, the nitrogen desorption from molten steel to the gas phase was more rapid than the nitrogen absorption of slag from the molten steel. The rate determinations step of nitrogen desorption from molten steel is changed from the interfacial chemical reaction step to the mass transfer of the metal phase, depending on the reduction of oxygen and sulphur in metal.
  • Mechanism for Separating Inclusions from Molten Steel Stirred with a Rotating Electro-magnetic Field

    pp. 142-149

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    DOI:10.2355/isijinternational.32.142

    An experimental model was constructed to clarify the mechanism for separating inclusions from molten steel strongly stirred with a rotating electro-magnetic field.
    Molten steel was rotated and solidified in a crucible. The ingot obtained had its maximum oxygen content at the axis of rotation. The existence of this maximum area can be partly explained by the centripetal force acting on inclusions during rotation of the mnolten steel.
    Many coagulating inclusion pairs were observed in the ingot, with the radii of the inclusions forming coagulating pairs being concentrated in the range from 10 to 50 μm. This phenomenon was explained using Saffman's model, which shows the probability of gradient collision between inclusions in turbulent eddies. This inclusion coagulation effect suggests the high deoxidation capability of rotating molten steel in an electro-magnetically stirred ladle.
    x

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    2. Formation of Cementite from Titanomagnetite Ore ISIJ International Vol.46(2006), No.5
    3. Analysis of Oxide Dispersion during Solidification in Ti, Zr-deoxidized Steels ISIJ International Vol.32(1992), No.1
  • Filtration Mechanism of Non-metallic Inclusions in Steel by Ceramic Loop Filter

    pp. 150-156

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    DOI:10.2355/isijinternational.32.150

    For the reduction of non-metallic inclusions in steel, a ceramic loop filter has been developed. Void size of the filter can be adjusted widely by varying the string and loop diameters respectively. Characteristics of the loop filter, such as an inclusion removal efficiency and filter medium resistance were investigated in laboratory. From the experimental results, the mechanism of the filtration was discussed, and it was concluded that firstly the inclusion particle is entrapped onto the filter surface by the interception, secondly glued there by the attraction force based on the molten steel surface tention, and finally bonded by sintering.
  • Removal of Inclusion from Molten Steel in Continuous Casting Tundish

    pp. 157-163

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    DOI:10.2355/isijinternational.32.157

    The chemical compositions of tundish flux were studied to decrease oxygen content in molten steel in the tundish. Production scale experiments revealed that high basicity flux (CaO/SiO2≥11.0) is superior in decreasing oxygen content, compared with low basicity flux (CaO/SiO2=0.83). Oxidation and deoxidation rates in the tundish were evaluated quantitatively based on the experimental results. Mathematical model was developed to make clear the behavior of oxygen concentration and to predict the change in oxygen concentration during casting. The effects of influential factors on the change in oxygen concentration were discussed.
    x

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  • Mechanism of Alumina Deposition on Alumina Graphite Immersion Nozzle in Continuous Caster

    pp. 164-168

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    DOI:10.2355/isijinternational.32.164

    Alumina graphite rods were immersed in liquid iron to clarify the mechanism whereby continuous caster immersion nozzles made of alumina graphite were clogged. Even when aluminum was not contained in the iron melt, alumina formed and deposited on the surface of the alumina graphite rod in contact with the iron melt. This experimental result suggests that alumina in the alumina graphite nozzle is reduced by graphite to suboxide gas, and the suboxide gas diffuses to the contact interface with molten steel and is reoxidized into alumina at the interface. This reaction is accelerated by silica in the alumina graphite nozzle.
  • Analysis of Oxide Dispersion during Solidification in Ti, Zr-deoxidized Steels

    pp. 169-173

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    DOI:10.2355/isijinternational.32.169

    The control of oxide dispersion is one of the most important factors in the newly explored field of study "oxides metallurgy in steels, " utilizing fine oxide particles as heterogeneous nucleation sites for various precipitates. The distribution of oxides in the solidification structure is greatly influenced by interactions between the oxides and the advancing solid/liquid interface as solidification progresses. In order to clarify the behavior of oxides in steels during solidification, unidirectional solidification experiments was conducted. The distribution of oxides was quantitatively analyzed by CMA, and the experimental results were discussed in comparison with a mathematical calculation taking account of microsegregation and precipitation during solidification. In Ti-deoxidized steel, Ti2O3 segregated in the interdendritic region considerably more than calculated. The discrepancy means, that considerable numbers of oxides were rejected to the interdendritic region by advancing solid/liquid interface during solidification. In Zr-deoxidized steel, on the other hand, ZrO2 distributed relatively uniformly, as expected from calculation. The difference between both species of oxides regarding the rejection/entrapment phenomena is most likely due to interfacial energy between the liquid steel and oxide particles.
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    2. Formation of Cementite from Titanomagnetite Ore ISIJ International Vol.46(2006), No.5
    3. Large Inclusions in Plain-carbon Steel Ingots Cast by Bottom Teeming ISIJ International Vol.46(2006), No.5

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