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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 62 (1976), No. 3

  • 鉄鋼の研究における競争と協調について

    pp. 313-314

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  • Mathematical Model of the Shaft Furnace for Reduction of Iron-Ore Pellet

    pp. 315-323

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    A mathematical model of the shaft furnace is developed for gaseous reduction of iron-ore pellet. In the model, the reduction of iron-oxide is defined as the multi-stage successive reaction and the reduction rate equations are derived from the multi-interface core model in a single pellet.
    This model is applied to the simulation for the changes of reduction degree in an experimental shaft furnace which has 0.1 m in diameter and 4.0 m in height. It has been found that the model is able to simulate well the reduction behavior in the furnace and the rate constants obtained from the simulation calculation of the experimental data are nearly close to those of the former literature about the fundamental research of the reduction of iron-ore pellets.
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    Readers Who Read This Article Also Read

    1. Analysis of Operating Conditions of Shaft Furnace for Reduction of Iron-Ore Pellet by Using a Mathematical Model Tetsu-to-Hagané Vol.62(1976), No.3
  • Analysis of Operating Conditions of Shaft Furnace for Reduction of Iron-Ore Pellet by Using a Mathematical Model

    pp. 324-333

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    A mathematical model having the multi-interface model for the reduction of single pellet is employed for the theoretical analysis of the commercial operating conditions of shaft furnace and the following results are obtained.
    (1) The required bed height for the reduction is linear to the productivity of iron per cross sectional area of furnace under the same composition and utilization of reducing gas.
    (2) The temperature of injection reducing gas greatly affects the required bed height. Under the each operating condition, the critical temperature exists and it correlates to the equilibrium point from Fe3O4 to FeO reduction by hydrogen on the operational line chart of oxygen exchange in shaft furnace.
    (3) The reduction by the gas contained carbon-monoxide is more effective than that by only hydrogen because of the magnitude of the reaction heat.
    (4) Being below 10%, the H2O and CO2 in reducing gas do not bring a large shortcoming on the process.
    (5) The increasing of gas pressure until about 5 atm has a marked effect to the reduction rate and the productivity becomes larger, the higher the pressure goes, then the shaft furnace having the pressure over several atmospheres is desirable.
    x

    Readers Who Read This Article Also Read

    1. Mathematical Model of the Shaft Furnace for Reduction of Iron-Ore Pellet Tetsu-to-Hagané Vol.62(1976), No.3
  • Rates of Nitrogen Absorption into Liquid Fe-Cr and Fe-Cr-Ni Alloys

    pp. 334-343

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    The rates of nitrogen absorption of inductively melted liquid Fe-Cr and Fe-Cr-Ni alloys have been measured at 1600°C by Sieverts method.
    The apparent mass transfer coefficient of nitrogen absorption of those alloys, KN, decreases with increasing oxygen concentration as already observed for liquid iron. In the range between 0.01 and 0.03% O, it has been observed that the values of kN of those liquid alloys are smaller than those of liquid iron, although there are little differences between them below 0.01% O or above 0.03% O.
    The surface tensions of liquid Fe-Cr and Fe-Cr-Ni alloys were estimated from the experimental results of nitrogen absorption of those alloys, in order to ascertain the behavior of adsorbed oxygen at the gasmetal interface.
    According to the obtained surface tension for those liquid alloys, it is probable that the excess quantities of adsorbed oxygen at the gas-metal interface of liquid alloys may be higher than those of liquid iron in low oxygen level. On the contrary, in high oxygen level, they may be lower than those of liquid iron.
    Consequently, the values of kN may change with the behavior of adsorbed oxygen at the interface. The differences of the apparent mass transfer coefficient among Fe-18Cr, Fe-18Cr-8Ni and Fe-25Cr-20Ni alloys are negligibly small. Silicon, vanadium and manganese have little effect on the values of kN for liquid Fe-18Cr-8Ni alloy.
  • On the Kinetics of C-O Degassing from Liquid Iron by Argon Stream

    pp. 344-353

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    This study aims at the kinetic investigation on the reaction between gas and liquid iron. A liquid iron droplet was levitated in a pure argon stream and the rates of carbon and oxygen removal from the droplet were measured. The CO absorption and degassing-rates were also measured by using crucibles. The reaction proceeds according to C+O=CO until one of these elements is eliminated. The reaction is found to be controlled by the transfers of the element from iron bulk to gas-melt interface and of CO from the interface to gas bulk. This mechanism can explain the different reaction behaviors between the levitation technique and the crucible melting method. In the case of the crucible melting method, the reaction proceeds complicatedly depending on the extent side reactions between the iron melt and the crucible. On the basis of the results obtained, a discussion has been made on the degassing reaction occurring in some practical process.
  • Rate of Removal of Carbon and Oxygen from Liquid Iron

    pp. 354-361

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    A model has been proposed to describe the rate controlling mechanism of CO removal from liquid iron and tested experimentally by blowing Ar gas onto the inductively stirred iron at 1580°C. The apparent rate constant k′ [cm/%-sec] calculated from the equation-d [%C] /dt=k′ (A/V) [%C] [%O] varies markedly with [%C] / [%O]. On the other hand, linear relationship is obtained between 1/k′ and [%C] in the concentration range [%C] >-0.03 and between 1/k′ and [%O] in the concentration range [%O] >-0.06. It is shown that the reaction rate is controlled by mass transfer rate of carbon in the melt in the range of higher oxygen and lower carbon concentration or by mass transfer rate of oxygen in the range of higher carbon and lower oxygen concentration. The transition composition of melts between the two steps is expressed by CC/CO=kO/kC The results are explained fairly well by the proposed reaction model.
  • Inclusions in the Mechanical Capped Steel

    pp. 362-371

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    A study on the macroscopic inclusion in the rim and core zones of large mechanical capped steel ingots (23t-34t weight) has been carried out. The slime method was utilized for extracting inclusions.
    (1) In the lenticuler blow holes in the rim zone there are many large macroscopic inclusions. A part of these inclusions is a glassy oxide which is made from (Fe. Mn) -Si-Al-O, and another part is a large lumpy inclusion which is made from Al2O3.
    (2) The former inclusions (glassy oxides) which from a tortoise shell-shape stick on the inner side of lenticuler blow holes, and the latter (Al2O3) which forms a lumpy type pops out into lenticular blow holes.
    (3) In the blow holes in the core zone there are large lumpy almina inclusions, and there are more in the upper part of the core zone than in the middle and the bottom part.
    (4) These large lumpy inclusions are caught by the blow holes in the core zone and carried by them into the inner part of the zone.
    (5) However, in the blow holes at the core zone no inclusion of the tortoise shell-shape is found.
  • Quenching Abilities of Sprayed Jet Cooling and Air Blast Cooling

    pp. 372-379

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    With the purpose of utilizing sprayed jet cooling and air blast cooling to the heat treatment of the steel the heat transfer coefficient α was measured and some considerations were given.
    The main results obtained are as follows:
    a) Air blast cooling
    Following empirical formula are obtained with the range of experiments, 3×103Re≤2×104, 0.02≤D≤0.04 [m] and 100≤T≤600 [°C].
    Nua=3.25Re0.45 (D/D0) -0.1 (v/v0) 0.2
    Nua: Nusselt number Re: Reynolds number
    D: diameter of specimen disc v: velocity of air D0=0.03 [m] v=8.94 [m/sec]
    b) Sprayed jet cooling
    1. There are three stages in the cooling process; they are termed as the high temperature, transition, and low temperature stages. The cooling mechanisms in these stages are considered.
    2. In the high temperature stage, α is the sum of those of air blast cooling and the cooling due to evaporation of water droplets.
    3. The fraction of water quantity, K, which is effective for cooling by evaporation in the high temperature stage does not change with the water quantity and the temperature, when the sprayed jet velocity is constant.
    4. The value of K increases with v. In the range of this experiments following equation is obtained.
    K=3.2×10-v v: [m/sec]
  • Some Properties of High-Speed Tool Steel Powders Atomized with Water

    pp. 380-389

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    Martensite, residual austenite and, carbides in the powders of two kinds of high-speed tool steels, SKH 57 and SKH 9 (JIS) atomized with water were examined in as-atomized state and tempered states mainly by means of X-ray diffraction analysis. The main results are as follows:
    (1) There is more residual austenite in the powders in as-atomized state than in conventionally solidified and quenched high-speed steel. The lattice parameters of both martensite and austenite in the powders are larger, and the tetragonality of martensite is smaller than that estimated from their carbon content, because of high supersaturation of alloying elements.
    (2) By tempering of powders at 300°C, the lattice parameter and tetragonarity of martensite are decreased, but the residual austenite is still stable. By tempering at 550°C, alloy carbides in MC-type are precipitated and the amount of residual austenite is decreased.
    (3) Internal stress measured by a line broadening in X-ray diffraction profile is not high in the as-atomized state, and increase with secondery hardening during tempering. It corresponds to the secondary hardening behaviour of the steels.
    (5) Alloy carbides (MC+M2C) are distributed in network in as-atomized powders. The network is gradually broken down by tempering at 550°C, and at 750°C the carbides are spheroidized and transformed into M6C, while a small amount of MC is still remained.
  • Stress Corrosion Cracking Behavior of Austenitic Stainless Steels in MgCl2 Solutions

    pp. 390-398

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    Stress corrosion cracking behavior of SUS 304 and SUS 316 stainless steels was investigated in terms of concentration and temperature of MgCl2 solutions with or without dissolved oxygen. The potential-MgCl2concentration relation between SCC and pitting corrosion was also studied by constant potential method under the applied stress of 25 kg/mm2.
    As dissolved oxygen becomes necessary to cause SCC with decreasing the concentration or the temperature of MgCl2 solutions, SUS 316 becomes much more resistant to SCC than SUS 304. The crack is often observed originating at the bottom of a pit.
    The lower limit of MgCl2 concentration above which cracks develop at 80°C is about 20% for SUS 304 and about 25% for SUS 316, while the critical SCC potential of SUS 316 is about 50 mV more noble than that of SUS 304. Above the lower limit of MgCl2 concentration, the corrosion mode shifts from SCC to pitting corrosion as the applied potential is raised and the SCC potential range widens with increasing MgCl2 concentration. Below that, only pitting corrosion occurs.
  • Diffusion Layers of Electroplated Chromium on Plain Carbon Steels

    pp. 399-407

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    Investigations have been carried out on steel/chromium diffusion couples, which were prepared by electrodepositing chromium on various plain carbon steels. Influences of carbon contents in the steels used as materials, of heat treatment temperature, and of holding time on the structure, composition, hardness etc., of produced diffusion layer were studied.
    The results are summarized as follows:
    1) The diffusion layer is formed even after heat treatment at a comparatively low temperature such as 600°C. On all the steels, the produced diffusion layers are of about 85% in Cr concentration.
    2) When heat-treated at a higher temperature than 800°C, the steel has a diffusion layer of the composition different from that in (1), the layer being of about 75% in Cr concentration. In this system, as the material contains carbon, the produced polyphase diffusion layer is different from that observed in the Fe-Cr system and changes according to the temperature range.
    3) Formation of the diffusion layer hardly depends on carbon content of the material and the thickness of the layer is almost constant for all the carbon contents.
    4) In the diffusion layer of a high Cr concentration, carbon is locally saturated and the layers of constant-carbon cencentration are formed which contain more carbon than in the steel. It appears that, chromium carbide and double carbide of iron and chromium may be formed but the existence of those carbides could not be proved by X-ray diffraction, perhaps because of their too small amounts.
    5) The produced diffusion layer has a comparatively good resistance against hydrochloric acid, picric acid etc., and its hardness, as one of mechanical properties, is as high as 1 000 or more in HK, which may be typical of carbide.
  • Biamperometric Acid-Base Titration of Slags in Molten Salts

    pp. 408-413

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    Several slags were titrated biamperometrically by the following two methods. First, the sample slags were allowed to react with potassium dichromate in molten potassium nitrate at 400°C, and then the excess parts of the dichromate were titrated back with the sticks of the nitrate containing potassium carbonate in definite concentration. Secondly, the samples were allowed to react with vanadium pentoxide in the eutectic mixture of lithium, potassium, and sodium sulfates at 650°C, and the excess parts of the pentoxide were titrated back with the weighed portions of the carbonate. Well defined titration curves could be obtained, indicating the reversible electrode reaction of the acids (the dichromate and the pentoxide).
    The results of these titrations were enough reproducible. The amounts of the acids consumed by the sample slags were compared with the basicity indexes of each slags which were calculated from various methods based on the composition obtained by chemical analyses. Almost linear relationship could be obtained by both methods between the amounts of the acids consumed and the following basicity indexes; they are basicity ratio, V-ratio, the basicity by GRANT and CHIPMAN, the basicity by KERLIE and that by MORI. These conclusions are nearly the same as those of the previous report.
  • High Temperature Bearing Steel and Anti-Corrosion Bearing Steel

    pp. 414-423

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  • The Steel Industry in Japan and Great Britain

    pp. 424-434

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  • Report of the Ironmaking Committee of the Joint Research Society of ISIJ

    pp. 435-440

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  • Report of the Steelmaking Committee of the Joint Research Society of ISIJ

    pp. 441-447

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  • 転換期対応策における前提条件を考える

    pp. 448-448

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  • 抄録

    pp. 449-457

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