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

Tetsu-to-Hagané Vol. 56 (1970), No. 6

  • Analysis of Sintering Process by the Mathematical Model

    pp. 661-670

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    A mathematical model of sintering process has been developed, in which considerations have been given to the combustion of coke, drying process of solid, the composition of lime stone and the meltingand solidifying process of iron ore. Variations of physical properties of gas and solid particles with the change of temperature have been taken into consideration.
    The partial differential equations gave numerical values, at various depths in the bed and at various times, of the temperature of solid particles and gas, the radius of coke and lime stone particles, the concentration of O2 and CO2 gas, the combustion velocity, the decomposition rate of lime stone, the moisture content of solid and the melting rate of iron ore. Typical results are illustrated.
  • Kinetics of Re-oxidation of the Sponge-Iron Powders

    pp. 671-682

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    Kinetic studies of the re-oxidation of the sponge-iron powders reduced in the temperature range 400 to 800°C from ferric oxides and Brazilian iron-ores have been carried out at various partial pressures of oxygen in the temperature range 300 to 800°C.
    The characteristics of the sponge-irons during oxidation have been determined by means of four methods (gravimetric, microscopic examinations, X-ray diffraction and surface area measurements). Following results were obtained.
    1) Oxidation of sponge-irons proceeds very rapidly by exposure to oxidizing atmosphere and then proceeds slowly. The latter obeys logarithmic law.
    2) As those sponge-irons are oxidized, their specific surface areas increase and then decrease gradually.
    3) The structure of the oxide layers are examined by X-ray diffraction; generally, magnetite is observed as a main component, accompanying small amounts of hematite.
    4) The early rapid re-oxidation is regarded as gaseous diffusion control and latter slow oxidation obeys the logarithmic oxidation law.
  • Study on Classification Accuracy of Pneumatic Sieve

    pp. 683-694

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    The classification method by pneumatic sieve has been developed to eliminate fines in ores charged into blast furnaces. When particles are supplied into air stream upward, smaller particles float up and larger one sink down. In this method, the apparent specific weight, the drag ccefficient of the particles, and the interference of moving particles in the air stream (especially between floating-up and sinking-down particles) affect the classification accuracy.
    In this paper, the above effects are experimentally and theoretically discussed. Conclus: ons are as follows;
    (1) The classification by pneumatic sieve is available with the difference of floating velocity of particles, even if apparent specific weight and drag coefficient scatter in some extent.
    (2) The scattering of apparent specific weight and drag coefficient affects the classification accuracy significantly for the particles of diameter nearly equal to the floating particle diameter Ds and negligibly for the particles of diameter less than half of Ds.
    (3) For the classification of particles in the same particle size distribution, the weight ratio in each size range of floating-up particles to supplied one decreases logarithmically with increasing mixing ratio M.
  • Rate of Oxidation of Silicon in Liquid Iron by Oxidizing Gas

    pp. 695-707

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    For the purpose of investigating the transfer rate of silicon in steelmaking process, oxidation rate of silicon in liquid iron was measured by blowing oxidizing gas onto the surface of Fe-Si alloys melted in magnesia crucible, and relations among the rates of oxidation of silicon, carbon and manganese were examined.
    It was found that oxidation rate of silicon in liquid iron was strongly influenced by the nature of slag formed on the surface of melt during run.
    In the system containing carbon, preferential oxidation of carbon was observed because CO is thermodynamically more stable than SiO2 under experimental conditions which are high temperature and low pressure of cabon monoxide.
    In the system containing manganese, silicon and manganese were oxidized simultaneously and the rate of oxidation of silicon increased with increase of flow rate of oxidizing gas. In this case it was supposed that the rate of reaction was controlled by the diffusion of oxidizing gas in the gas phase.
  • A Few Phenomena on the Occurrence of Large Inclusion in Bottom Part of Low Carbon Rimming Steel Ingots

    pp. 708-715

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    In the rimming steel ingots, large inclusions exist characteristically in the bottom part of ingots. The formation of large inclusions is related to the formation of “mushy zone” which grows up from bottom of molten steel in mold during the period of rimming action.“Mushy zone” can be observed macro-scopically at the cross-section of solidified ingot.
    The result of investigation of tested ingots under the various conditions indicates that amount of large inclusions in “mushy zone” increases with increase of height of “mushy zone”. Rimming time and height of ingot have an important influence on the growth of“mushy zone” or amount of large inclusions. It is observed that when rimming time becomes longer or ingot becomes higher, both height of “mushy zone” and amount of large inclusions increase.
  • Mechanism of Formation of Tetragonal Chromite

    pp. 716-726

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    In order to investigate the formation mechanism of the tetragonal chromite formed in molten Fe-Cr alloys, the authors have studied the influence of oxygen partial pressure and temperature on the axial ratio of the tetragonal chromite formed from the solid solutions between Fe2O3 and Cr2O3 in an atmospheres of various CO2-H2 mixtures or H2 gas.
    The results obtained are summarized as follows:
    1) The oxide coexisting with molten Fe-Cr alloy at 1600°C varies from cubic, via tetragonal chromite, to Cr2O3 in accordance with oxygen partial pressure. When the mixing ratio of CO2-H2 is 1/16 or 1/18, the following three phases equilibrate. They are tetragonal chromite (c/a=0.95), sesquioxide and molten Fe-Cr alloy.
    2) Single phase region of chromite becomes enlarged with temperature rise and the chromium ion in chromite increases. Tetragonal chromite having axial ratio c/a=0.90 was obtained with H2 reduction at 1850°C.
    3) The following equations were derived to lattice parameters of tetragonal chromite. a=a0/γ·{(1+2γ2)/3} 1/2 andc=a0 {(1+2γ2)/3} 1/2, where γ is tetragonality (c/a) and a0 is 8.37Å
    4) The determination of Cr2+ was tried with chemical means, but it was unadequate to confirm quantitatively.
  • Study on Phase Diagram of Fe-Cr-O System

    pp. 727-733

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    To study the defect structure in tetragonal chromite, its density, thermogravimetic, property, electric resistance and thermo e. m. f. were measured.
    Furthermore the influence of nitrogen or carbon on the formation of tetragonal chromite was studied.
    The results obtained are as follows:
    1) The effect of nitrogen or carbon on the formation of the tetragonal chromite was not determined.
    2) Results from thermogravimetric studies have shown good agreement with those from X-ray studies.
    3) Isothermal phase diagram of Fe-Cr-O system at 1 600°C was established. The relationshp between the chromium content of Fe-Cr melt and the oxide phase equilibrated was determined. below 1% Cr-cubic chromite, 1-7%Cr-c/a=1-0.95 above 7% Cr-Cr2O3
    4) From single phase region of chromite, the chemical composition of chromite having axial ratio c/a=0.95 was determined as (Fe0.26·Cr0.74) 3.04O4.
    5) Defect structures in cuLic and tetragonal chromites were confirmed.
  • An Origin of the Recrystallized Grains with Preferred Orientations in Cold Rolled Fe-3% Si Alloy

    pp. 734-750

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    The origin of the preferred recrystallized texture (011)[100] in cold rolled (111)[211] single crystals of Fe-3% Si was studied by observing changes in microstructures while heating foil specimens inside a 500kV electron microscope, and by determining the statistical distribution in orientations of small recrystallizing grains.
    The formation and the growth of subgrains are found to be a continuous process, in which the size of cells or subgrains increases gradually through ‘cooperative rearrangement’ of the subgrain boundaries; in other words, a composite process of boundary decomposition, combination and migration.
    The subgrain growth is enhanced in the regions of heavily curved lattice, where the (011)[100]-oriented cell groups are embeded. The (011)[100] grains grow appreciably larger than other grains in the later stages of rearrangement, and extensively according to the rapid migration of the high angle boundaries in the final stage.
    The predominance of the (011)[100] orientation in the recrystallized textures is the result of the (011)[100] subgrains to be far larger in number than that of the other recrystallizing grains. The preferred formation of the (011)[100]-oriented cell groups and subgrains was discussed, as proposed by CAHN, on the basis of the accumulated dislocations belonging to a predominant slip system in the rolling deformation.
  • Relation between Austenitizing Time and Mechanical Properties of High-Speed Steel

    pp. 751-759

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    In the earlier paper dealing with the underhardening of high-speed steel of 6-5-4-2 type, the effects of the austenitizing temperature and the holding time at the temperature on the mechanical properties were reported. And then the time was constant, that is, 45 sec.
    The present work was undertaken to determine the effects of heating temperatures and times of wider ranges than those of the previous work, e. g. the austenitizing temperatures were 1160°C and 1200°C for press tools and 1240°C for cutting tools, and the immersing times were 10-3000 sec and tempering temperatures were 200-625°C.
    The results obtained are as follows:
    (1) If underhardening is employed for press tools (1160°C for quenching and 300°C for tempering), tne longer the immersing time the better the bend strength.
    (2) In case of cutting tools, a good abrasive resistant property is obtained when the steel is tempered at 550°C, and a high bend strength is associated with the hardness values of Hv 800-850.
    (3) If better toughness rather than red hardness is required for tools, the tempering temperature should be as high as 600°C. By this tempering the range of bend strength over 400 kg is very wide.
    (4) When quenched hardness are about Hv 800, microstructure is consisted of residual carbides and the mixture of martensite and austenite. And this structure is obtained when immersing time is over 300 sec at 1160°C, 100 sec at 1200°C and 30 sec at 1240°C.
    (5) The higher the temperature and the longer the time of immersing, the larger the austenite grains grow. And particularly, when austenitizing temperature is higher, the effects of immersing time on austenite grain-size are remarkable.
    (6) When the austenitizing temperature is low or immersing time is short, the grain-boundary disappears by the low tempering. But in case of the high temperature and long immersing time, the grain-boundary disappears by the tempering at about 500-525°C.
  • Effect of Additions of Ti, Nb, V and Ti, Nb, B on Creep-Rupture Strength of High-Mn Austenitic Steel

    pp. 760-771

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    The effects of further addition of V or B to 18% Cr-6%Ni-8% Mn steel with small amounts of Ti and Nb, which has been found to have high creep-rupture strength and to be very economical, on creep-rupture strength are investigated.
    As a result, it was found that the addition of V in the range of 0.3 to 0.5% is effective to raise the creep-rupture strength at relatively low temperatures (600 to 650°C) for shorter times and the addi. tion of B up to 0.05% is effective to raise the creep-rupture strength at relatively high temperatures (650 to 750°C) for longer times. The effect of V is considered to be mainly due to solutionhardening, and the element rather accelerates the coalescence of carbide at high temperatures. The effect of B is considered to be depressing the precipita;ion and especially the coalescence of carbide.
    These steels have to be improved further for practical applications, i. e. both steels have considerable amount of delta ferrite resulting in poor hot workability, especially this is further pronounced in the boron bearing steel due to the existence of boride within the composition range of this work.
    The resistance to high-temperature oxidation was also investigated for those steels in air and in gasturbine atmosphere with blast furnace gas as fuel.
  • Effect of Precipitation Phases on the Mechanical Properties of 25Cr-2ONi Heat-Resistant Cast Steel

    pp. 772-783

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    Effects of precipitation phases on the mechanical properties at room temperature and on the creep rupture strength at 800°C of 25Cr-20Ni heat-resistant cast steel containing carbonranging from 0.06 to 0.4% were investigated. The results obtained were summarized as follows:
    (1) With increasing the aging time at 800°C, massive σ-phase of angular type whichexisted in the as-cast specimen with 0.06% of carbon changed to the shape of globular type, and the widmanstatten type appeared in the grain. Changes of the amount and the shape of the σ-phase hadan important influence upon the creep rupture strength and the ductility.
    (2) Both eutectic carbides of M7C3 and M23C6 which existed on the grain boundaries of the as-cast specimen with 0.2% of carbon began the in situ transformation to σ-phase after the aging for 300 hr and substituted completely the σ-phase for the carbides after the aging for 5 000 hr. The structural unstability due to the in situ transformation of carbides to σ-phase deterioratedr emarkably the creep rupture strength and the elongation.
    (3) The eutectic carbides in as-cast specimen with 0.4% of carbon were identified mainly to M23C6, the shape and the amount of which were not changeable even after long period of aging. After the aging for 1000 hr, secondary carbides were observed in the grain and the coalescence of these carbides decreased the creep rupture strength.
  • Relation between Hydrogen Embrittlement Behavior and Stress Corrosion Cracking of Austenitic Stainless Steel under Anodic and Cathodic Polarization

    pp. 784-795

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    In order to study the behavior of hydrogen embrittlement under anodic and cathodic polarization of austenitic stainless steels, were measured the change in ductility and amount of adsorbed hydrogenin the 18Cr-8Ni and 25Cr-20Ni stainless steels in H2SO4, HCl, NaCl and MgCl2 solutions.
    The main results obtained are as follows:
    (1) Hydrogen absorption and embrittlement occurs in chloride solution under anodic polarizationbut not in H2SO4 solution.
    (2) This hydrogen adsorption was closely connected with the operation of local corrosion cell sassociated with pits on the surface of the steel.
    (3) It is significant that the pitting and the associated hydrogen adsorption in these steels play animportant role for stress corrosion cracking. Therefore impressed anodic current can reduce the stresscorrosion cracking time.
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  • Metallographic Analysis of Microarnount of Boron in Boron Treated Steel

    pp. 796-806

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    This paper is a part of the general investigation of new mefallographic analyses for steel. A simple and reliable method is described for the metallographic analysis of microamount of boron in boron treated steel, by a new electrolytic extraction method using NaCl-EDTA solution as an electrolyte.
    The procedure is as follows:
    1. Separation of boron compound from steel.
    (a) Cover the steel sample with close-texture filter paper as a diaphragm, connected as an anode, is dissolved into 100 to 150ml of 1% NaCl-5% EDTA electrolyte (pH 6-7) at a current density of 50mA/cm2 for 2 to 4 hr. Remove the anode, and residue is collected into the filter paper. Transfer the paper and residue to a quartz beaker, and 20ml of HNO3 (1: 2) and boil for 5min.
    (b) Filter and wash with hot water. Add 12ml of H2SO4 (1: 1) and 6ml of H3PO4 (1: 1) to the filterate and evaporate to copious fumes. Dissolve the salt with 50ml of water, cool, dilute to 250ml, and determine boron as carbide continue in accordance with section 2.
    (c) Add 12ml of H2SO4 (1: 1) and 10ml of H2O2 to the electrolyte and boil for 30min, cool, dilute to 250ml, and determine boron as solid solution continue in accordance with section 2.(d) Transfer the paper and residue (Paragraph (b)) to a quartz beaker, add 20ml of HCI (1: 1) and boil for 10min.
    (e) Filter and wash with hot water. Add 1 ml of HNO3 (conc.), 6ml of H2SO4 (1: 1) and 4 ml of H8FO4 (1: 1) to the filterate and evaporate to copious fumes. Dissolve the salt with 10ml of water, cool, dilute to 100ml, and determine boron as oxide continue in accordance with section 2.
    (f) Transfer the paper and residue (Paragraph (e)) to a platinum crucible, and ingnite. at 500°C. Add 1g of Na2CO2 and heat gradually until fusion is complete. Cool, take up the melt in 6 ml of H2SO4 (1: 1), and dilute to 100ml, and determine boron as nitride continue in accordance with section 2.
    2. Determination of boron compound. Transfer 25 in/ of each of the solution of section 1.(b), (c), (e), and (f) to.separatory funnel. Add 10ml of water and 5ml of HF (5%) and let stand for 1hr. Add 20ml of water, 2ml of methylene blue solution (0.001M) and 25ml of dichlorocthane, and shake for 1min. Let stand for 5 min to allow the layers to separate. Filter the dichlorosthane solution through a dry filter paper into a dry absorption cell. Measure the absorbance against blank solution at 660μ.
  • Installation of Sub-lance for LD Converter

    pp. 807-812

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    Water-cooled type sub-lance 12.8 in in length and 216 mm in outer diameter is installed in No 1 LD furnace of No 2 steel making plant in Tobata Area Works, in order to catch the condition of LD process. It is inserted into LD vessel through the upper-hood at an incline of 74° with a speed of 2-60 m/min by means of manual or automatical remote control. Measurements can be performed within 75-450 sec with expendable sensors set in the head of sub-lance.
    Three types of sensors with a single function are prepared and applied to process analysis as follows:
    1) Level sensor: to measure the change of bath level depending on lining life and that of foaming slag level during blowing.
    2) Temperature sensor: to measure the change of bath temperature during blowing.
    3) Sampler: to take a sample from metal bath during blowing. Sub-lance is effective in an LD process control and process analysis.
  • Spectrophotometric Determination of Microamount of Boron in Steel by Solvent Extraction with Tetrafluoroborate-Methylene Blue Complex

    pp. 813-818

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    A simple spectrophotometric method is described for the determination of microamount of boron invarious steels by solvent extraction with tetrafluoroborate-methyleneblue complex. The procedure is asfollows:
    Dissolve 1g of the sample in 20m1 of HNO3 (1: 1) or 20 ml of aqua regia, add 15 ml of H2SO4 (1: 1) and 15m1 of H2PO4 (1: 1), evaporate to fumes of H2S04, cool, and dilute to 250ml withwater. Transfer 25 ml of the solution to separatory funnel, add 10 ml of water and 5 ml of HF (5%) and let stand for I hr. Add 20 ml of water, 2 ml of methyleneblue solution (0.001M) and 25 ml ofdichloroethane, and shake for 1 min. Let stand for 5 min to allow the layers to separate. Filter thedichloroethane solution through a dry filter paper in to a dry absorption cell. Measure the absorbanceagainst blank solution at 660mμ. The procedure needs less time than any other methods reported in the past literature.

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