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

Tetsu-to-Hagané Vol. 77 (1991), No. 10

  • Neural Network Models and Its Applications to Iron and Steel Making Processes

    Yoshihisa OTSUKA, Masami KONISHI

    pp. 1539-1543

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Problems of Bainitic Transformation and Microstructures in Low Carbon Steels

    Toru ARAKI, Masato ENOMOTO, Koji SHIBATA

    pp. 1544-1550

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  • Report of Domestic Marine Transportation Subcommittee

    Masanori YOSHIZAKI

    pp. 1551-1560

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  • Estimation of Void Fraction and Shape Factor in Moving Bed of Sinter and Coke

    Morimasa ICHIDA, Youichi ISOZAKI, Kenji TAMURA

    pp. 1561-1568

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    Abstract

    The influence of size distribution of charged materials in blast furnace on void fraction and shape factor was analyzed by using a experimental apparatus in which void fraction and pressure drop under the countercurrent moving bed can be measured. The relation between the void fraction and the particle diameter in uniform-sized coke and sinter is not simple, but the minimum values of the void fraction exist at a certain particle diameter. The minimum values of the void fraction in coke and sinter composed of two component particles are obtained at the range of 0.3 to 0.5 in fractional volume of fine particle. The estimation equations of the shape factor of coke and sinter are obtained so that the measured values of the pressure drop can agree with the calculated value of the pressure drop by Ergun equation. According to these equations, the shape factors of coke and sinter increase from 0.4 to 1.0 with increasing the particle diameters of coke and sinter. The estimation equation of the void fraction of sinter applicable in the actual blast furnace operation was proposed by correcting the estimation equation of the void fraction in randomly packed bed of multi-component particles, proposed by Suzuki, based on the measured values of the void fraction in the moving bed of sinter.

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    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Kinetics of Reduction Step of Wustite to Iron in Gaseous Reduction of Quaternary Calcium Ferrite

    Takayuki MAEDA, Yoichi ONO

    pp. 1569-1576

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    Abstract

    As a fundamental study for clarifying the reduction phenomena of sintered ore in a blast furnace, quaternary calcium ferrite was synthesized from chemical reagents of Fe2O3, CaCO3, SiO2, and Al2O3 and the kinetic behavior at the final stage of reduction of the quaternary calcium ferrite with CO and H2 gas was studied.
    The results obtained are summarized as follows:
    (1) Reduction rate increased with an increase in temperature both in CO and H2 reductions. The increase of reduction rate with temperature was not very large above 900°C but it was remarkably large between 800°C and 900°C.
    (2) Reduction at 900°C and above proceeded topochemically both in macro- and microstructures. At 800°C, the reduction did not proceed topochemically but rather homogeneously.
    (3) Reduction data at 900°C and above were analyzed based on the unreacted-core model. Reduction curves calculated by using the rate parameters obtained by the analysis agreed with the observed data very well. Temperature dependencies of the chemical reaction rate constant kc and the effective diffusivity in the product layer De were given by following equations:
    kcCO = exp (13.28-164.9×103/RT ) (m/s) (1 1731 273 K)
    DeCO = exp (-7.16-32.07×103/RT ) (m2/ s) (1 1731 273 K)
    kcH2= exp (3.62-55.83×103/RT ) (m/s) (1 1731 273 K)
    DeH2= exp (-3.61-53.91×103/RT) (m2/s) (1 1731 273 K)

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    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Kinetics of Water Gas Shift Reaction with the Catalysts of Metallic Iron and Nickel

    Fengman SHEN, Reijiro TAKAHASHI, Jun-ichiro YAGI

    pp. 1577-1584

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    Abstract

    An attempt was made to clarify the reaction mechanism and to determine the rate parameters for water gas shift reaction with solid metal as catalyst. For the reaction, the influence of gaseous adsorption on the surface of metal catalyst played an important role. In the present work, both lumpy iron and spherical nickel were used as catalysts and the rate of water gas shift reaction was observed at pressure range of 0.13 to 1.01 MPa. Adsorption of gas species was experimentally found to surpress the reaction. The rate equation of water gas shift reaction was derived on the basis of the Temkin's adsorption theory as follows:
    -rCO2=kapp(pCO2pH2-pCOpH2O/K)/pmCO2pnH2
    The parameters of kapp, m and n in the above equation were determined from the results of experiments. Calculated values based on the rate equation agreed well with observed data.
    The order of catalytic activity of various catalysts at 873 K in the basis of unit area and unit time was found as follows:
    Lumpy iron>Spherical nickel>Reduced iron pellet (reduced at 1 273 K by hydrogen)

  • Simulation Model of the Gas-Liquid Flows in the Packed Bed

    Jiabing WANG, Reijiro TAKAHASHI, Jun-ichiro YAGI

    pp. 1585-1592

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    Abstract

    A mathematical model was presented to describe the countercurrent flows of gas and liquid through packed beds for analyzing flow phenomena in a blast furnace.
    For the gas flow, the vectorial form of Ergun's equation was used as equation of motion. For the liquid flow in the packed bed, flowing region was obtained by a dispersion-probability model using a flow network system for the dispersed flow. Liquid flow vector in the flowing region was computed from the Darcy's equation that was derived for the continuous liquid flow.
    A series of experiments was conducted by a two dimensional cold model for measuring the liquid flow region, liquid distribution at the receivers and gas pressure distribution in the packed beds. The experimental data were simulated well by the mathematical model presented in this paper. In addition, the model estimated the dry zone formed in front of gas inlet.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Mathematical Two-dimensional Model of the Blast Furnace Process

    Mamoru KUWABARA, Shinji TAKANE, Kunio SEKIDO, Iwao MUCHI

    pp. 1593-1600

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    Abstract

    A mathematical two-dimensional model is developed for analyzing inner circumstances of blast furnace at steady state operation. This model is consisted of a set of partial differential equations representing simultaneous processes of gas and burden flows, heat transfer and mass transfer with chemical rate processes. Derivation of governing equations, evaluation of transport parameters and a finite difference scheme for stable and effective computation of the large scale model are shown in this paper.
    On the basis of a thermodynamic consideration of Si-O-C system, the mechanism of SiO formation in the dropping zone of blast furnace is considered to change from an equilibrium of SiO2-C to that of SiC-C at higher temperature where SiC becomes stable. The evolved gaseous SiO is kinetically reduced by dissolved and saturated carbon in hot metal.
    The inner circumstances of a blast furnace with pulverized coal injection are numerically analyzed using the two-dimensional model, and the characteristics of distributed process variables are examined in comparison with those at all coke operation.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Analysis of Oxygen Blast Furnace Process Based on a Mathematical Simulation Model

    Hideyuki YAMAOKA, Yasuo KAMEI

    pp. 1601-1608

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    Abstract

    Theoretical study was made to search an effective use of oxygen in the blast furnace with a one-dimensional blast furnace mathematical model and following results were obtained.
    1) The straight use of oxygen in the blast will result in the increase of the fuel rate because of the lack of heat at the furnace shaft caused by the excessive increase of the flame temperature.
    2) The use of oxygen with the combined use of the pulverized coal in large quantities is reasonable to restrain the excessive increase of the flame temperature and both the low fuel rate and the high productivity will be achieved without any other measures such as the hot gas injection into the furnace shaft.

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    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Maximum Injection Rate of Fine Ore through Tuyeres into Blast Furnace

    Kazuyoshi YAMAGUCHI, Hiromitsu UENO, Masaaki NAITO, Kenji TAMURA

    pp. 1609-1616

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    Abstract

    In order to obtain the maximum fine ore injection rate, an experimental apparatus capable of simulating the heat transfer and reaction in the lower part of the balst furnace was built. This apparatus is 0.90 m3 in inner volume, is a 90° sector in cross section, is one-fifth of the actual blast furnace in height and is equipped with one tuyere.
    As a result of the fine ore injection through the lance which was inserted through the blow pipe, the maximum fine ore injection rates at which the desired deadman temperature can be maintained were experimentally determined as shown below. The maximum fine ore injection rate in the actual blast furnace is expected to be higher than those measured here.
    ·The injection of the 0% prereduced fine ore alone is difficult.
    ·70 g/Nm3 for injection of the 0% prereduced fine ore mixed with the same amount of pulverized coal.
    ·175 g/Nm3 for injection of the 60% prereduced fine ore alone.
    ·115 g/Nm3 for injection of the 60% prereduced fine ore mixed with the same amount of pulverized coal.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Influence of Ore to Coke Ratio Distribution on Descending and Melting Behavior of Burden in the Blast Furnace

    Morimasa ICHIDA, Kazuhiro NISHIHARA, Kenji TAMURA, Masayasu SUGATA, Hajime ONO

    pp. 1617-1624

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    Abstract

    The influence of ore/coke distribution on the descending and melting behaviors of burden was analyzed by using a three-dimensional semicircular warm model of the blast furnace under conditions set as similar as possible to the physical phenomena in the furnace. If the ore/coke in wall region is locally increased, the descending velocity increases and the gas flow velocity decreases in that region. An increase of +0.1 in the heat-flow ratio in the wall region of bosh results in a decrease of about 5°C (80°C in the value converted into that of the actual blast furnace based on the Stanton number) in the wall temperature of bosh. At the all coke operation, as the wall temperature in the lower part of the furnace tends to decrease, the ore/coke near the wall should be preferably decreased by the charging of ore closer to the furnace center. At the high-rate coal injection operation, as the melting capacity near the wall is large, the ore/coke in the wall region should be preferably increased and the ore/coke in the center region should be preferably decreased by the charging of ore farther from the furnace center.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Reduction of Silicon in Hot Metal by Iron Ore and Flux Injection through Blast Furnace Tuyere

    Kanji TAKEDA, Yoshitaka SAWA, Seiji TAGUCHI, Nobuhiro TAKASHIMA, Toshiyuki MATSUMOTO, Hiroshi OBATA

    pp. 1625-1632

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    Abstract

    A Multi-Purpose Injection (MPI) System was installed at Chiba No. 5 blast furnace and a test operation on the injection of iron ores and fluxes was conducted twenty one days for the purpose of lowering silicon content in hot metal. The results obtained from the trial are summarized as follows:
    1. Reduction of silicon content of 0.08% in hot metal was obtained by the mixed powder injection of iron ore and flux powder of 5.0 kg-CaO/t. It was suggested that the major factor inducing the silicon reduction was the absorption of SiO(g) by the injected powder. That was made on the basis of sampling examination by a sideways tuyere probe.
    2. Significant reduction of silicon content was not observed during the iron ore powder injection up to 50.4 kg/t with constant coke rate. On the other hand, increases of (FeO) and [S] indicated that the oxygen potential in a hearth became higher by the iron ore powder injection.

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  • Mechanism of Hanging Caused by Dust in a Shaft Furnace

    Hideyuki YAMAOKA

    pp. 1633-1640

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    Abstract

    The mechanism of hanging caused by the dust in reducing gas in the reduction shaft furnace was investigated. Through experimental studies using a rectangler model and theoretical studies using a two dimensional mathematical simulation model, it was clarified that the dust in reducing gas sticked on the packed particles to form a dust blockade zone in front of tuyered and when the dust concentration of reducing gas was high or the descending velocity of packed bed was low, the dust blockade zone was expanded and the gas pressure drop was increased to cause hanging.

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  • Experiment of Phosphorus and Oxygen Distribution between CaO-SiO2 MgO-FetO Slag and Liquid Steel and Estimation of Phosphorus Content at End Point of Top and Bottom Blowing Converter

    Tsutomu USUI, Kenzo YAMADA, Yoshihiko KAWAI, Shigeru INOUE, Hiroaki ISHIKAWA, Yoichi NIMURA

    pp. 1641-1648

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    Abstract

    The phosphorus and oxygen distribution between CaO-SiO2-FetO slag and molten steel has been obtained in the temperature range from 1 600 to 1 700°C. They can be expressed by the following equations.
    log[(%P2O5)/{[%P]2(%FetO)5}]=11.20 log {(%CaO)+0.3(%MgO)-0.05(%FetO)} +29 600/T-36.25 (i)
    log(γFetO) =0.0257(%SiO2)-0.300 (ii)
    It has become clear that phosphorus and oxygen distribution between slag and molten steel at end point of 250t top and bottom blowing converter has attained equilibrium by investigating the data at end point on the basis of equations (i) and (ii). Solving the phosphorus distribution equilibrium and the mass balance equations has made it possible to estimate phosphorus content at end point with high accuracy.

  • Characteristics of Electric Power and Heating of Molten Steel of AC Plasma Torch for Arc Heating of Molten Steel in Tundish

    Hideaki FUJIMOTO, Tadashi SAITO, Motoyoshi SHIMIZU, Norio KIYOKAWA, Hideki IRITANI, Seiji NISHI

    pp. 1649-1655

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    Abstract

    The single A. C. plasma arc heating system was adopted in the new No. 4 continuous caster at Kakogawa works in 1989 to keep molten steel temperature constant during casting. By using this system, the effect of atmosphere on plasma arc voltage and the heating characteristics of molten steel were investigated. The obtained results are as follows:
    Plasma arc voltage in the case of using molten steel is lower than that of using carbon block because of existence of metallic fume. Plasma arc voltage is affected by the gas composition more than the dust quantity in the tundish and it increases with increasing the content of gas molecules such as O2 and N2 gas in the Ar atmosphere. It is possible to keep molten steel temperature constant in the tundish by the suitable plasma arc heating condition.

  • Production of High Purity Silicon by Carbothermic Reduction of Silica Using AC-arc Furnace with Heated Shaft

    Yasuhiko SAKAGUCHI, Makoto FUKAI, Fukuo ARATANI, Masato ISHIZAKI, Tetsuro KAWAHARA, Mitsugi YOSHIYAGAWA

    pp. 1656-1663

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    Abstract

    To produce inexpensive solar-grade silicon of high purity, a AC-arc furnace has been developed based on a thermodynamic consideration of carbothermic reduction of silica to metallic silicon. The furnace is featured by a closed type shaft and a hearth with arc electrodes and feeding nozzles. The carbon pellets as a reducing agent are fed from the top of the shaft, whereas silica powder is transferred to the hottest arc spot in the hearth. The resulting species of SiO and SiC, generated through the reactions of SiO2 + C →SiO + CO and SiO + 2C →SiC + CO, react in the lower part of the shaft to yield silicon, SiO+ SiC →2Si + CO. Melting silicon is accumulated in the hearth and pulled out from the tapping hole.
    The productivity has been about 2 kg/h and the silicon yield has been found to be typically 83%. Analyses have shown that the impurities in the silicon were below 0.1 ppmw for B, 12 ppmw for Fe and below 5 ppmw for the other elements. Single-crystalline solar cells fabricated starting from this silicon after purifications of decarburization and unidirectional solidification have recorded a conversion efficiency of 16.5%. This value was equivalent to that of solar cells made from semiconductor-grade silicon.

  • Fluid Flow in Ladle and Its Effect on Decarburization Rate in RH Degasser

    Yoshiei KATO, Hakaru NAKATO, Tetsuya FUJII, Shigeru OHMIYA, Seiji TAKATORI

    pp. 1664-1671

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    Abstract

    Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate at RH degasser.
    The results of hydrodynamic calculation on fluid flow in ladle was proved to be reasonable compared with results in cold model experiments. Decarburization reaction model coupled with fluid flow in ladle made it clear that decarburization reaction rate obtained from the model is higher than that for perfect mixing flow and lower than that for plug flow. The model enabled us to predict the concentration distribution of carbon in ladle during decarburization treatment. The maximum value found in the recirculating flow zone becomes about twice the minimum one which is obtained in the region just below the down-leg. Dead zone is not recognized, which disturbs the decarburization rate in the process. It was also made clear that shape of ladle does not have any significant effect on the decarburization rate.

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  • Temperature Measurement during Rapid Solidification of 18Cr-8Ni Stainless Steel and Its Initial Solidification Structure

    Hideo MIZUKAMI, Toshio SUZUKI, Takateru UMEDA

    pp. 1672-1679

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    Abstract

    A new measurement system using a silicon photo-diode was developed to investigate the precise thermal history during the initial solidification of stainless steel. From the measured cooling curve, it was confirmed there existed large undercooling before nucleation. Maximum undercooling obtained was 260 K. The undercooling increased with the cooling rate of a sample and has a strong linear dependence on the cooling rate. In the vicinity of the sample surface, the initial solidification layer was formed, which had cellular structure of metastable austenitic phase. Effect of undercooling on the micro and macro structure was also investigated quantitatively.

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  • Forging Method for Consolidating Loose Structure in Steel Ingot with V Shaped Dies

    Kunio ISOBE, Hidetami NOGUCHT, Kazunori KATO

    pp. 1680-1687

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    Abstract

    The moire techinque is used to measure the two and three dimentional deformation of round billets in forging with 135°V dies. Each billet is made by piling up 0.75 mm thin white plasticine sheets painted with black ink. From the observation of moire fringes an Octagonal Forging Method (OFM), characterized by sequential billet rotation through 0° 90° 135° 225° in the cross section, is proposed to consolidate the loose structure in the wide area of ingot center. Strain distributions for various cross sections in a billet are observed by the moire method. No deformation takes place in the center of the billet near the die edges. A plasticine ingot is forged according to the OFM by axially shifting the ingot by the full die-width or 1/4 of the width. A comparison of axial strain distribution is made between two ingots thus obtained. A 3%Cr steel shaft by the full die-width shifting method with the OFM has loose structure remaining at the center ; the locations of the loose structure correspond to the small axial strain regions. Loose structure in another 3%Cr ingot is consolidated by the 1/4 die-width shifiting method with OFM.

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  • Behavior of Under-film Corrosion on Zn and Zn-Fe Alloy Coating in Salt Spray Environment

    Kimitaka HAYASHI, Yoichi ITO, Yasuhiko MIYOSHI

    pp. 1688-1694

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    Abstract

    The observation and analysis have been carried out at under-film corrosion tip of Zn and Zn-Fe alloy coated steel sheets after salt spray test.
    It has been attempted to investigate the coating corrosion mechanism with electrochemical method and to elucidate the correlation between the durability of coating against chlorine penetration and the composition of Zn-Fe alloy coating.
    As a result, following five conclusions have been obtained.
    (1) Corrosion of coated steel sheets proceeds by coating-precedence corrosion mechanism.
    (2) Initial corrosion product of coating is chloride of zinc.
    (3) Durability of coating against chlorine penetration is mainly due to coating itself corrosion resistance.
    (4) Coating corrosion under paint proceeds by charge transfer controlled corrosion mechanism.
    (5) Coating corrosion is mainly due to contribution of corrosion current by way of micro circuit between coating and iron substrate.

  • Theoretical Investigation of Under-film Corrosion on Zn, Zn-Fe Alloy Coated Steel Sheets

    Kimitaka HAYASHI, Yoichi ITO, Yasuhiko MIYOSHI

    pp. 1695-1701

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    Abstract

    For the purpose of the theoretical explanation on Cl- penetration behavior of Zn and Zn-Fe alloy coating investigated phenomenologically, the modeling of coating corrosion at under-film corrosion tip has been attempted and the balance of corrosion current by way of two micro circuits was formulated.
    The coating corrosion distance (Cl- penetration distance) and the effective length of the iron substrate contributing the formation of corrosion circuit between coating and iron substrate, the distribution ratio of corrosion current by way of circuit on coating to total coating corrosion current were required quantitatively.
    As a result, it made clear that the physical shap of coating corrosion circuit was defferent between atmospheric exposure and salt spray environments.

  • Graphite Pollusion Mechanism at the Surface of Steel Sheet on Annealing

    Takayuki NAKAMURA, Motoo SATO

    pp. 1702-1709

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    Abstract

    Graphite can occur on the steel surface when the cold rolled steel sheets are batch-annealed under non-oxidizing atmosphere. The mechanism of graphite formation was studied by examining the influence of annealing atmosphere and temperature on graphitization reaction and the main results are summarized as follows. (1) Oxygen present on the steel surface plays the most important role and is indispensable to the graphite formation. (2) CO gas generated by the reaction with the solute carbon in steel and the oxygen in oxide film on the surface is decomposed into graphite and CO2 gas. (3) The graphite formed in a carburizing atmosphere with some extent of CO gas shows the same morphology of the graphite formed in non-oxidized atmosphere, and CO gas in an annealing atmosphere requires the critical partial pressure, 0.1 atm, for the graphite formation on steel sheet. (4) The dependency of oxide film thickness on crystallographic orientation of iron may be responsible for the orientation dependence of graphite formation.

  • Effect of Reduction of Cold Rolling on Secondary Recrystallization of Grain-oriented Electrical Steel Produced by Single-stage Cold Rolling Process

    Shozaburo NAKASHIMA, Kunihide TAKASHIMA, Jiro HARASE

    pp. 1710-1716

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    Abstract

    Previouly, authors reported the effect of the reduction in cold rolling which is an important factor for secondary recrystallization of the grain-oriented electrical steel produced by the single-stage cold rolling process by varying final thickness.
    Then, the effect of the reduction was overlapped with that of final thickness. This time, a study has been made concerning with the effect of the reduction on secondary recrystallization by varying the thickness of hot-bands, i.e., by keeping final thickness in the same level. The following are conclusions.
    (1) With the increase in the reduction, at first, the size of the secondary grains gets larger, then, fine grains begin to appear among large secondary grains, and finally, fine grains occupy all part of the specimen.
    This phenomenon is considered to be attributed to the decrease in the nuclei of (110) [001] orientation accompanied by the increase in the reduction.
    (2)With the increase in the reduction, the orientations of secondary grains concentrate on the ideal (110) [001] orientation.
    This phenomenon is considered to be attributed to the increase in the intensity of the ∑9 coincident orientation with the ideal (110)[001] orientation in the primary matrix.

  • Effect of Inhibitor on Secondary Recrystallization of Grain-oriented Electrical Steel Produced by Single-stage Cold Rolling Process

    Shozaburo NAKASHIMA, Kunihide TAKASHIMA, Jiro HARASE

    pp. 1717-1724

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    Abstract

    A study has been made on the effect of inhibitors on the secondary recrystallization of the grain-oriented electrical steel produced by the single-stage cold rolling process.
    (1)The specimen with MnS doesn't secondary-recrystallize at all. One with AlN partially does. Another with MnS and AlN completely does.
    (2) For secondary recrystallization of Goss texture, the specimen with MnS and AlN has such following advantageous features as (a), (b) and (c) as compared with the specimen with MnS, and as (b) and (c) as compared with the specimen with AlN.
    (a) Strong effect of inhibition on the boundary migration of primary grains during the heating period of final annealing.
    (b) Small average size of primary grains.
    (c) Strong densities of {110} and {111} poles in primary texture. That is, probably, abundant Goss nuclei and the texture easy to be consumed by Goss oriented grains.

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    1. Development of a Simulation Testing Machine for Evaluating the Lubricity of Lubricant in Cold Sheet Rolling Tetsu-to-Hagané Vol.74(1988), No.4
    2. Characteristics of Ni-Sn-Zn Alloy Coated Steel Sheet by Thermal Diffusion Method Tetsu-to-Hagané Vol.77(1991), No.7
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  • Influence of Solution Treatment under Unrecrystallized Austenite (Unrecrystallized Solution Treatment) on Strength and Toughness of 18% Ni Maraging Steel with Various Strength Level

    Takuya YASUNO, Kazuhiko KURIBAYASHI, Ryo HORIUCHI, Masahisa OTSUKA

    pp. 1725-1732

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    Abstract

    In 18% Ni maraging steel whose strength level is from 2.0 GPa up to 2.4 GPa, the relation between plane strain fracture toughness, KIC, and tensile strength, σB. is experimentally given by
    KIC∝σB n n 4.
    Crack growth of the present alloy is controlled by micro-cleavage and their subsequent ductile coalescence. Increase of the strength level brings about increase of areal fraction of micro-cleavages and the resultant decrease of KIC. Solution treatment under the condition of unrecrystallized austenite (unrecrystallized solution treatment) results in strengthening and toughening due to remarkable refinement of martensite structure, particularly the block dimension. In the alloy whose strength level is beyond 2.4 GPa, however, unrecrystallized solution treatment dose not cause toughening. The reason behind is that the critical grain size which is necessary for ductile fracture has to become much smaller than that which is realized in usual unrecrystallized solution treatment.

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    Readers Who Read This Article Also Read

    1. Development of a Simulation Testing Machine for Evaluating the Lubricity of Lubricant in Cold Sheet Rolling Tetsu-to-Hagané Vol.74(1988), No.4
    2. Characteristics of Ni-Sn-Zn Alloy Coated Steel Sheet by Thermal Diffusion Method Tetsu-to-Hagané Vol.77(1991), No.7
    3. Structural Analysis of Black Nickel Deposits on Electrogalvanized Steel Sheet Tetsu-to-Hagané Vol.77(1991), No.7
  • © 1991 The Iron and Steel Institute of Japan

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