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

Tetsu-to-Hagané Vol. 54 (1968), No. 12

  • Diffusion in Iron Oxide Melts

    pp. 1199-1203

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    The interdiffusivity of iron and oxygen in iron oxide melts has been measured by the capillary method in a temperature range from 1430 to 1550°C and for a composition range from r (=Fe3+/ΣFe)=0.12 to 0.42. At 1550°C, the interdifrusivity is 4×10-4-5×10-5cm2/sec, which is very high as compared with the diffusivity of silicate slags. Activation energies for diffusion are 10.7±0.6 and 16.6±0.2 kcal/mol at r=0.12 and 0.33, respectively. The diffusivity decreases with increase of r.
    At higher Fe3+ content (r>-0.25), this decrease of diffusivity becomes to a larger extent. The observed results are interpreted with relation to the constitution of the melts and other properties such as electrical conductivity and viscosity.
  • A Study on the Formation and Reduction of Fayalite (Fe2SiO4)

    pp. 1203-1216

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    In this work, the rate of formation of fayalite (Fe2SiO4) from mixture of ferrous oxide and α-quartz was measured. The influence of various oxide additions on the formation of fayalite was also studied. These synthetized samples were reduced with H2 or in graphite crucible. The rate of reduction was measured, and reduction products were investigated with X-ray diffraction.
    The results obtained are as follows:
    1) The rate of formation satisfies with JANDER'S equation.
    2) The formation of fayalite was generally delayed by additions. The stoichiometric molar ratio of FeO/SiO2 was altered as a result of the reaction of added compounds with FeO and Si02.
    3) Especially, the formation of fayalite was delayed when magnetite and tridymite co-existed with fayalite as a reaction product.
    4) The rate of reduction agrees with MCKEWAN'S equation, during the early period of reduction. When the reduction proceeds further with formation of amorphous SiO2, MCKEWAN'S equation was not valid, since fayalite reduction is prevented by amorphous SiO2.
    5) FeO was reduced first in the samples which contain FeO and additions. The rate of reduction of fayalite was influenced little by additions.
    6) It is found that fayalite is decomposed into Fe and Fe2-xSiO4-y at the primary stage of reduction. When Fe2-gSiO4-y was reduced further, it changed to amorphous SiO2 at low temperature, and α-crystobalite at high temperature.
  • On the Formation of Calcium Ferrite in Sintered Ore

    pp. 1217-1225

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    Calcium ferrite phases in the sintered ores whose basicities were about 1.5 were investigated by the polished thin section method and X-ray microanalysis. They were hemicalcium ferrite containing Al2O3 of several to ten odd per cent and some of them included the very fine particles of calcium ferrite of ternary system or hematite precipitated in the cooling process. Hemicalcium ferrite was classified in four types, i. e. columnar, long columnar, acicular and dendritic. The formation mechanisms of the particles of each type are as follows: Columnar and long columnar ferrite is formed by the reaction of iron oxide with CaO in molten slag and their shapes depend on firing temperature and cooling rate. Acicular ferrite whose Al2O3 content are remarkably high grow from the ash of coarse coke particle. Dendritic ferrite is crystallized from the molten slag whose ratio of CaO to SiO2is small. The formation of the particle composed of two kinds of calcium ferrite is related to the change of the oxygen potential of the melt during crystallization.
  • On the Formation of Silicate Mineral in High Basicity Sinter

    pp. 1225-1231

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    The microstructures of the slag matrices in the industrial sinters with high basicity were investigated. The matrices are composed mainly of dicalcium silicate, melilite and glassy silicate. Small amounts of calcium ferrite and iron oxide, whose crystals are dendritic in many cases, are also contained. On the basis of the combinations of these minerals, the crystal-lization processes from the molten slag of the CaO-FeO-Fe2O3-Al2O3-SiO2 system are discussed. The matrices containing dicalcium silicate as the first primary phase are observed generally throughout the sample sinters, and those containing other primary phases are not generally. The formation of the latter is considered to be originated in the maldistribution of raw materials and the delay in the homogenization of the melt. The melilite particles, the non-precipitated silicate, which is formed by the reaction of coke ash and molten slag, is found only a little.
  • Effect of Multi-Stage Crushing on the Size Distribution Control of Crushed Product of Iron Ore

    pp. 1232-1241

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    The prevention of undesired fine particles production during the crushing of iron ores is one of the important problems in the blast furnace burden preparation.
    This paper presented a study on the size distribution of the crushed product of iron ores under various reduction ratios and on the benefit of the multi-stage crushing.
    Crushing experiments with several reduction ratios confirmed that the amount of fine particles in the crushed product increased with increasing the reduction ratio and that the size distribution of the crushed product agreed well with the GAUDIN-MELOY equation. The relationship between the size ratio r in the GAUDIN-MELOY equation and the reduction ratio R was obtained as the following equation with two constants, a and b;
    r=a (R)b
    Using the above results, the size distribution of the final product in any multi-stage crushing can be calculated.
    As a result, it is distinctly recognized that the multi-stage crushing benefits for the size distribution control of the crushed product.
  • Study on the Manufacture of Self Fluxed Pellets and the Use to Blast Furnace

    pp. 1241-1259

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    The paper presented the development of self-fluxing pellets and the availability in them to blast furnace of Kobe Work Ltd.
    Several phases of the pelletizing process are discussed individually, and also their relation to performance in blast furnace operation. Special emphasis is placed on proper preparation of the limestone added to the raw materials, and indurating at optimum conditions.
    Better quality of pellet will be gained by the proper size distribution of raw material the control of indurating temperature. The performance of blast furnace with self-fluxed pellets are also discussed.
  • On the Mineral Composition and the Formation of the Scaffold at the Shaft of Tobata No 1 BF

    pp. 1259-1267

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    The mineral compositions and formation mechanisms of the scaffolds, taken from Tobata No 1 BF were investigated. In the scaffold sample from the upper level of the shaft, coke breeze and fine or lamelar cementite are combined to the wall by zincite. It is thought that the fragmentation of a cementite particle occurs with the grain growth of matrix zincite and the lamination of cementite is caused by vigorous carbon deposition under the compressive force developed by the burden material. The scaffold rich in silicate from the middle level is estimated to be the sintered body of the particles of the iron are and the compounds formed in ascending gas. Samples. from the lower level of the shaft and the belly are composed mainly of kalsilite and they are formed by the reaction of firebrick of chamotte with alkali oxide. The measures for preventing the growth of scaffold in the shaft are discussed.
  • On the Behavior of Hydrogen in the Blast Furnace Top Gas

    pp. 1268-1271

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    Investigations were carried out on the behavior of hydrogen in blast furnace top gas.Relationship between hydrogen utilization ηH2 and carbon monoxide utilization ηco was found.
    It was given as
    ηH2=ηco+8
    With this euation it is possible to detect water leakage of tuyeres and cooling boxes of blast furnace.
  • Deboronization Phenomena in Surface Layer of Steel with Carburizing Process

    pp. 1271-1277

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    As the loss of boron from surface layer of steel during austenitizing should diminish from its beneficial effect, the authors investigated the characteristics of B-treated steel in view of practical effectscaused in the deboronization with the carburizing.
    First of all, the deboronization appeared with the decrease of the amount of effective B and the increase of the amount of ineffective B in the sense that itbecomes so remarkable while carburizing depth becomes deep, and the loss of effective B from carburizing surface brings about following changes on the hardness distribution of carburizing layer;
    1. As boron available for the decrease of the amount of retained austenite is lost, the lowering of hardness occurs in the outer part of carburizing layer.
    2. As the benefit of increasing hardenability by boron is lost, the practical hardening depth becomes remarkably thiner under the slow cooling condition, which is due to the large size of sample.
    Of course it would be possible to diminish these failures with the increase of previously contained amount of boron, but it would be impossible to eliminate the disadvantage that the amount of ineffective B-compound increases on the surface layer.
    To summarize, therefore, the characteristics of B-treated steel is in similar with higher alloy steel not containing boron which is used in small carburizing part with the thin hardening depth, to which unfavorable effect by the deboronization is ignored.
  • Behavior and Thermodynamic Properties of Tantalum Carbide and Nitride in Steels

    pp. 1277-1289

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    The structure, chemical composition and behaviors of tantalum-carbides and nitrides in steels were-studied by means of metallographic observation and chemical analysis as well as X-ray diffraction analysis of the residues extracted from various specimens of vacuum melted high purity Fe-Ta-C, Fe-Ta-N and Fe-Ta-C-N alloys containing tantalum up to 3.16%. The specimens were prepared from forged materials by solution treatment and long time holding at various temperatures from 1000 to 1300°C. The quantitative analysis of soluble-tantalum, -carbon and -nitrogen was also conducted in-order to calculate the solubility products of tantalum-carbide and-nitride in austenite.Results obtained are as follows;
    1) The precipitates of tantalum-carbides or-carbonitrides were observed predominantly on austenite grain boundaries as finely dispersed particles, while the tantalum-nitrides were precipitated as comparatively large particles.
    2) It was confirmed that these precipitates can be quantitatively isolated from the iron matrix by dissolving the chips in 6N-HC1 solution at room temperature.
    3) The precipitated tantalum-carbide or-carbonitride in these samples were identified to be f. c. c.δ-phase and their lattice constant decreased as the content of nitrogen in sample increased.On the other hand, the precipitated tantalum-nitrides in various specimens were identified to be h. c. p.γ-phase with almost same lattice constant.Intermetallic compound Fe7Ta3 was also found in the sample containing tantalum of more than 3%.
    4) The precipitated δ-phase was not pure carbide but carbonitride even in the Fe-Ta-C alloys containing little nitrogen and its chemical composition was determined to be TaC0.85N0.06.The precipitated r-phase was estimated to be pure tantalum-nitride TaN0.85.
    5) The solubility products of the tantalum-carbonitride and -nitride in austenite were given respectively by the following equations;
    log[%Ta] [%C]0.85 [%N]0.06=-5, 800/T+2.02
    log[%Ta] [%N]0.85=-7, 400/T+2.09
    6) It has been proved that oxygen has the stronger affinity to tantalum than carbon and nitrogen. in austenite.The preferential precipitation of a little amount of tapiolite [Fe, Ta (Nb)] O2 was recognized in all specimens.
  • On the Delayed Fracture of Low-Alloy High Strength Steels in Aqueous Environments

    pp. 1290-1297

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    A cantilever type testing apparatus for delayed fracture was developed to investigate the characteristics of delayed fracture in several aqueous environments for two kinds of low alloy high strength steels having a sorbitic and a martensitic structures the tensile strength of which were about 125kg/mm2 and 150kg/mm2 respectively.
    These steels were failed even in the air after a long period of time under high sustained stresses, and the fracture strengths were decreased in the sequence of air, water, pH 5-HCl solution, 0.1% NaCl solution, pH 3-HCl solution, 3% NaCl solution, 0.1 N-HCl solution and acetic acid solution saturated with H2S.
    The results of the observation of the fracture surfaces, crack initiation behaviour in delayed fracture and the quantitative analysis of hydrogen in steel lead the conclusion that the delayed fracture in these environments occurs by hydrogen induced from the surroundings, and the more active supply of hydrogen promises the lower fracture strength of the steel under sustained load.
  • The Reverse Transformation and the Accompanying Anomaly in Dilatation on Heating of Meta-stable Austenitic Stainless Steel

    pp. 1297-1310

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    An anomalous expansion in the dilatation curve of cold-rolled 18-8 stainless steel was incidentally found at about 530°C.The present experiments were made in order to clarify the cause of the anomalous expansion observed in the dilatation curve of some meta-stable austenitic Cr-Ni steels coldworked at various temperature, and also to clarify the behaviour of the reverse transformation of martensite to austenite in these steels, mainly by the thermal dilatation method and the micro-structural observations.
    When a cold worked 18-8 steel was heated at constant velocity of heating, the martensite in the steel transformed to austenite reversely step by step at the temperature range of 400-900°C.The first transformation began at 400°C, and the greater part of martensite transformed to austenite martensitically at 500-650°C, and the second at 680-760°C, the third at 800-900°C, respectively.However, the amount of transforming martensite decreased less and less as temperature raised.In such reverse transformation, the diffusionless process occurred at early stage and the diffusional process continued in after the first stage.The lath type martensite was separated along {111} plane, by growing austenite nucleated at that plane, and gradually thinned off.The second anomalous expansion was newly found in this experiment at the second reverse transformation temperature range, in addition to the anomalous first expansion previously found at the first reverse transformation range.The anomaly appeared in two phase steels consisting of the predominant martensite and retained austenite in proper phase ratio, regardless the steels were cold-worked or not.
    It was considered that the anomalous expansion is related to the martensite which transformed diffusionally and to the reverse transformation character of textured martensite to the certain oriented austenite.
  • The Effects of Oxygen and Carbon on Yield Point of α-Iron

    pp. 1311-1312

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    In order to study the effects of oxygen and carbon on mechanical properties in a-iron, tensile test were done on the specimens with various oxygen contents and on the carburized specimens with various oxygen contents.
    The results obtained here are as follows:(1) Yield point is lowered with the increase of oxygen content.(2) Ky value that is the coefficent of the grain size dependent term in PETCH relation σy=σi+Kyd-1/2, isaffected by oxygen, but σi is not.(3) In carburized specimens with various oxygen contents, the yield point is increased by carburizing and lowered with the increase of oxygen content.
  • Analytical Equipments and their Work Condition at Sakai Iron Plant

    pp. 1313-1323

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    New analytical equipments and their work condition at Sakai iron plant which produces steel ingots of 4, 500, 000t/ year are described. Main equipments, which analyse rapidly (about two minutes for one steel) and automatically iron, steel, slags and sinter, consist of an analytical computer (Quantac 502) belong to two photoelectric vacuum spectroscopic analysis apparatus (Quantvac) and a fluorescent X-ray analysis apparatus (VXQ). The analytical center is arranged in the office for converter plant. At the 1 st floor, an instrumental analysis room, a sample prepared room and a water analysis room is arranged. At the 2nd floor, two wet chemical analysis room, a fuel analysis room and a gas (in steel) analysis room is arranged. Also, the analytical center is connected to the converter plant, the blast furnace plant and the raw material testing center by the air shooter. The molten steel sample at the converter plant is shooted by the air shooter and is prepared automatically by the automatic sample preparater. Analytical results from Quantvac and VXQ is reported automatically by Quantac 502 as input of the process computer at the converter plant. Then, a, new type fluorescent X-ray analysis apparatus is made by Shimadzu Co., Ltd., is named VXQ-P, is attached the three program scanner and the two pulse height analyser, and is used analysis of iron ores.

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