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

Tetsu-to-Hagané Vol. 63 (1977), No. 7

  • 偶想

    pp. 1069-1070

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  • Kinetics of the Oxidation of Graphite by the Impinging Jet of Gas

    pp. 1071-1080

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    A study has been made of the oxidation rate of graphite by the impinging jet of CO2-CO mixtures, in order to analyze the mass-transfer characteristics in the gas phase in the reactor used for kinetic studies on the refining reactions between gas and molten metal.
    The results obtained are as follows:
    1) The rate of oxidation at 1500°C is cantrolled by the mass transfer in the gas phase. Average Sherwood numbers Sh (=kGd/D) are eorrelated by the eqnttion,
    Sh=n (rs/d) -1.5 (duρ/μ) 0.66 (μ/ρD) 0.5 (n=0.32±0.06),
    where kG is the mass-transfer coefficient for gas phase, d the inside diameter of nozzle, rs the radius of graphite specimen, u the velocity, ρ the density, μ the viscosity, and D the diffusion coefficient of gas. The properties of gas and u are calculated at the reaction temperature under atmospheric pressure, based on the composition and flow rate of the gas entering the reactor. Average Sherwood numbers for the decarburization of liquid iron estimated from published data are roughly consistent with those given by the above equation.
    2) The chemical reaction rate (-rA) of oxidation of graphite in carbon dioxide at temperatures from 1000°C to 1300°C is expressed by the equation,
    -rA=k1pSA (k1=117. 5exp (-43800/RT)),
    where k1 is the rate constant of the reaction (CO2+σ→CO+O·σ, σ=active site, O·σ=adsorbed oxygen), pSA the partial pressure of CO2 at the surface of graphite, R the gas constant, and T the reaction temperature.
  • The Chemical Reaction Rate of the Solusion Loss of Coke

    pp. 1081-1089

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    The chemical reaction rate of the solution loss with carbon dioxide was measured for conventional metallurgical coke and formed coke. The data for the rate obtained by the authors and other investigators were analyzed with several rate equations for the gasification of carbonaceous materials. The values of the apparent activation energy of the reaction obtained from these data were between 50 and 70 kcal/mol with the rate equations proposed by GADSBY, ERGUN, and TURKDOGAN-VINTERS. Furthermore, it was found that the values of the kinetic parameters were most uniform for all of these data with the Ergun equation, where the values of the apparent activation energy of the gasification and the enthalpy of the so called oxygen-exchange reaction were between 60 and 70 kcal/mol and between 14 and 17 kcal/mol respectively.
    In the presence of any neutral gas, the Ergun equation was of lower precision, because of only one gas composition term, Pco2/Pco in it. On the other hand, even in the presence of neutral gases, the rate could be expressed with a great precision by means of the Gadsby equation or the Turkdogan-Vinters equation; the latter was not so much precise as the former.
  • Heat and Mass Transfer in the Reduction of Single Hematite Pellet by Hydrogen

    pp. 1090-1098

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    The weight-loss and the variations in temperature at the center and the surface of a spherical hematite pellet were measured during H2 gas reduction in the bulk gas temperature range of 800°-1050°C.
    Two step temperature drop in the center of a pellet was observed in the reduction. It was proved by X ray diffraction that the first step mainly corresponds to the reduction of Fe2O3 to FexO, and the second step corresponds to the reduction of FexO to Fe. The surface temperature did not agree with the center temperature during the reduction.
    Applying the isothermal model and the non isothermal semi-unsteady model to the measured values, the applicability of the models was investigated. The reduction curves, which were calculated by both models, agreed with the measured values closely. The temperature variation predicted by non isothermal semi-unsteady model agreed with the measured value except the first step.
  • Step-wise Reduction of Hematite Pellets with CO-CO2 Gas Mixtures

    pp. 1099-1107

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    A series of reduction experiments was made in which hematite pellets were reduced stop-wise from Fe2O3 to Fe3O4, Fe3O4 to FexO, and finally FexO to Fe by CO-CO2 mixtures of appropriate compositions in the temperature range from 800 to 1050°C. The hematite pellets were made of pyrite cinder and the porosity was approximately 13%. Experimental data for each reduction step were analyzed in terms of the mixedcontrol kinetics based on the isothermal unreacted-core model.
    The results obtained are summarized as follows:
    (1) Rate constants for the reduction steps of Fe2O3 to Fe3O4, Fe3O4 to FexO, and FexO to Fe are expressed, respectively, by following equations:
    kcm=exp (7.768-18.92×103/RT) (cm/sec)
    kcw=exp (12.18-28.80×103/RT) (cm/m)
    kcFe=exp (12.70-29.91×103/RT) (cm/sec)
    (2) Labyrinth factors of the reduction product layers of Fe3O4, FexO, and Fe are expressed, respectively. by following equations:
    log10ξm-0.382×10-2T-5.352 (-)
    log10ξw=0.159×10-2T-2.467 (-)
    log10ξFe-0.124×10-2T-1.734 (T≥1 173K) (-)
    log10ξFe-0.102×10-1T-12.25 (T<1 173K) (-)
    (3) Reduction curves calculated for each reduction step by using the rate parameters based on the unreacted-core model are in satisfactory agreement with experiments.
    x

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  • Microsegregation in Low Chromium Steel Castings

    pp. 1108-1115

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    In order to elucidate the relationship between inhomogeneity of hardness and microsegregation of alloying elements in low chromium hypereutectoid steel castings, the distribution of chromium and carbon and the microhardness in both dendrite-arm and interdendritic regions were measured in iron-carbonchromium alloys containing 2-3% Cr. The effects of several other alloying elements such as silicon and nickel, which raise the carbon activity in solid state, on the segregation of chromium and carbon were also examined.
    The results obtained are summarized as follows;
    1) Segregation ratio of chromium is independent of chromium content up to 3% and increases with an increase of carbon content up to 1.5% above which eutectic appears.
    2) The difference of hardness between dendrite-arm and interdendritic regions is caused by the concentration difference of carbon between the both regions and is independent of the concentration difference of chromium.
    3) Carbon enrichment into interdendritic region is accompanied by the segregation of chromium because chromium gathers carbon into its rich region at the temperatures below the Acm line in the phase diagram. A small addition of silicon or nickel has no effect to prevent carbon enrichment.
  • Effects of Hot-rolling Conditions on Austenite Grain Size and Mechanical Properties of Hot-rolled Coil for High Test Line Pipe

    pp. 1116-1125

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    Effects of processing variables on the properties of high-strength, high-toughness hot rolled coils for high-test linepipe have been studied. Through laboratory and trial production tests using low C-high Mn-Nb-V and low C-high Mn-Nb-Mo steels, it has been confirmed that by the combination of lowering the slab reheating temperature to 1140-1170 at which some amount of Nb-carbonitrides is undisolved, and rough rolling of more than 85% reduction, an austenite grain size after rough rolling is refined to the ASTM 8. These conditions are essential to obtain final products with fine grained ferrite structure free from bainite and accordingly low ductile to brittle transition temperature, especially when the total reduction during finish rolling is limited to less than 50% due to a heavy thickness of the products.
    By controlling coiling temperature below 600°C, the yield strength is increased without impairing the transition temperature.
  • Effect of Mo on De-embrittling Behavior of Temper Embrittled Low Alloy Steels

    pp. 1126-1133

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    The effect of Mo content on de-embrittling behavior of 3.5% Ni-Cr-Mo-V steels was studied. Charpy specimens temper embrittled were rapidly heated to three defferent temperatures above the embrittling range and held for several seconds followed by quenching in water, using a high frequency heating device.
    The main conclusions obtained are as follows:
    (1) De-embrittlement behavior is rate-controlled by the diffusion process of embrittling species from prior austenite grain boundary to matrix and the diffusion rate is minimized by 0.25% Mo addition. Either decreasing or increasing Mo content leads to the increasing diffusion rate of embrittling species.
    (2) The activation energy for diffusion, 40kcal/mol, is independent on Mo content.
    (3) The variation of D with Mo content is in good agreement with the change of embrittling tendency with Mo content.
  • Delayed Fracture Crack Growth Characteristics of High Strength Steels

    pp. 1134-1143

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    The kinetirs of subcritical crack growth in distilled water under sustained loading for a JIS SNCM 8 steel (AISI 4340) tempered at 250°C (D125) and 430°C (D143), and for an SNCM 23 steel (AISI 4320) tempered at 200°C (D 220) were investigated in connection with their crack morphology. It was observed that the threshold value of stress intensity factor (KISCC) was not clearly influenced by temperature but the critical stress intensity factor for terminal fracture increased with increasing temperature for D125 and D143. It was shown that this increase was attributed to the microbranching of crack in those steels in which the crack path was intergranular. The crack growth rate was found to be linearly dependent on K in the range studied for D125 and D220, while approximately constant for D143. In all the cases the crack growth rate increased with temperature, indicating activation energies of about 9000 cal/mol and 8500 cal/mol for D143 and D220 respectively, but a strong K dependence of activation energy was found in the case of D125. It was indicated, however, that a single value of about 9000 cal/mol could be obtained even for D125 by the compensation of the effect of microbranching on crack growth rate.
  • Influence of the Precipitation of the Primary Carblde or Ferrite on the Incubation Period for Bainitic Transformation

    pp. 1144-1149

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    In this investigation, the change in incubation period for isothermal bainitic transformation was observed with precipitation of primary carbide or ferrite from the austenite before the transformation in hypereutectoid steel JIS (SUJ 2) or hypo-eutectoid steel JIS (SNCM 8), respectively. The main results are as follows:
    (1) The incubation period for upper bainitic transformation is remarkably shortened with the precipitation of the primary carbide, while that for pearlitic transformation is slightly affected.
    (2) The incubation period for upper bainitic transformation is also remarkably shortened as the content of carbon in austenite is decreased.
    (3) The incubation period for upper bainitic transformation is prolonged with the precipitation of the primary ferrite.
    (4) The incubation period for lower bainitic transformation is shortened with the percipitation of the primary ferrite.
  • The Effects of Some Factors on the Creep Behavior of Type 304 Stainless Steel

    pp. 1150-1159

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    The effects of some factors on the creep behavior of type 304 stainless steel have been studied, and relationships between the strength and the structures in the steel have been discussed. Main results obtained were as follows:
    (1) Greep strength and creep rupture strength at 550, 600, and 650°C increased with cold working rate up to 20%, but creep rupture elongation decreased. These facts were explained by the strengthening of matrix by dislocations which acted as precipitation sites of carbides during creep.
    (2) The steel was aged for up to 3000h at 550-700°C. Carbides precipitated on grain boundary and in the neighborhood of grain boundary. With long time or high temperature aging creep strength and creep rupture strength decreased, but creep rupture elongation increased.
    (3) Creep strength at 600°C was independent of the grain size. Initiation of crack was accelerated with growth of grains, and therefore the creep rupture strength and elongation became lower.
    (4) Creep strength of type 304 stainless steel stemed from uniformly distributed fine carbieds (Cr, Fe) 23C6 which precipitated on dislocations during creep.
    x

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  • Reaction Mechanism of the Sheet Galvanizing

    pp. 1160-1169

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    The relation between the changes of the alloy layer structures and diffusion paths, for galvanized steel sheets, has been investigated and kinetics of the alloy layer growth and iron dissolution are discussed.
    Any type of the alloy layer structures corresponds to one of the diffusion paths on the Fe-Zn-Al ternary phase diagram. The growth of the inhibited alloy layer follows the reciprocal logarithmic low. The outburst structure, where the δ layer is destroyed and penetrated by liquid zinc, grows linearly with time. The growth of the alloy layer containing the thick compact δ layer follows the parabolic law. The inhited alloy layer transforms to the outburst structure by an autocatalytic reaction. When immersion time is short, the alloy layer is considered to be in a metastable state and the solubility of iron at the solid-liquid interface presumably rises above the equilibrium solubility. Therefore, the rate of iron dissolution increases and iron can dissolve in the iron saturated bath. When the alloy layer contains the outburst structure, the δ particles spall off into the bath, which constitutes the mechanism of iron transfer to the bath. Except for the above cases, iron dissolves in proportion to the concentration difference between the equilibrium solubility and iron in the bath.
  • On the Surface Analysis of Steel Sheet by Fluorescent X-ray

    pp. 1170-1176

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    A quantitative analysis of sticking materials on steel sheet surface was made possible by fluorescent X-ray according to a following method.
    1. Preparation of standard samples:
    A known quantity of standard solution of element to be analyzed was placed on steel sheet in area where X-ray irradiated and then dried. The quantity of the placed element divided by the area was called “sticking density”.
    2. Drawing of calibration curves:
    Differences of X-ray counting rates after and before placing standard solution were plotted against sticking densities and calibration curves were drawn.
    3. Precisions and lower limits of determination:
    For example, standard deviation was 0.0148μg/cmcm2 for Na at 0.566μg/cmcm2 and 0.0048μg/cmcm2 for Cl at 0.252μg/cmcm2.
    Lower limit was 0.121μg/cmcm2 for Na and 0.038μg/cmcm2 for Cl.
    Conclusively, determination of sticking soil-materials on steel sheet surface which caused to rust initiation and films produced by chemical treatments were made possible without establishment of a chemical analysis method.
  • Effects of Deformation Rate and Temperature on Mechanical Properties of Temper-embrittled Nickel-Chromium Steels

    pp. 1177-1183

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    Temper embrittled nickel-chromium steels were subjected to the impact and static tensile tests and Charpy test in the temperature rangefrom ambient temperature down to that of liquid nitrogen, in order to investigate the effect of deformation rate on yield and tensile strengths and the variation of ductile brittle transition temperature with carbon content and austenite grain size.
    The variation of yield and tensile strengths with decrease of temperature was found to be significantly different between temper embrittled and unembrittled specimens. In temper embrittled specimens, the ducile-brittle transition phenomena similar to Charpy test was observed in the impact tensile tests and the strength of the specimens intergranulally fractured in a brittle manner was constant irrespective of austenite grain size and deformation rates.
    The relationship between the transition temperature and lnd-1/2 (d: austenite grain size) was linear regardless of deformation mode and rate. The slope of these lines was estimated to be 125°C/cm1/2, which is larger than that of mild steel. This result suggests that the ductile-brittle transition phenomena of temper embrittled steels are significantly depend on austenite grain size.
  • Effect of Heat Treatment on Fatigue Strength of Gas-Chromized Cr-Mo Steel

    pp. 1184-1190

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    For the purpose of clarifying the effect of heat treatments on the fatigue strength of gas-chromized Cr-Mo steel, three kinds of samples of Cr-Mo steel SCM22, that is, one annealed, quenched and tempered, diffusion treatment after gas-chromizing with CrCl2, and the other gas-chromized, quenched and tempered after a preliminary carburizing, have been subjected to a rotary bending test in the ambient atomosphere, and the results are as follows:
    (1) Annealing after gas-chromizing provides a fatigue strength lower than that without gas-chromizing.
    (2) Quenching and tempering after gas-chromizing provides a fatigue strength lower than that without gaschromizing.
    (3) The lower fatigue strength of chromized samples is considered to be due to decarburized zone under the Cr diffusion layer.
    (4) Therefore, through the diffusion treatment followed by the gas-chromizing, fatigue strength of the steel is improved.
    (5) Furthermore, it has been confirmed that the gas-chromizing after carburizing have increased fatigue strength of the steel.
  • Problems in the Utilization of Solar Energy

    pp. 1191-1199

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  • 部会報告

    pp. 1200-1206

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  • 第92回講演大会討論会報告

    pp. 1207-1211

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  • Report of 5th International Conference on Vacuum Metallurgy and Electroslag Remelting Processes

    pp. 1212-1214

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  • 抄録

    pp. 1216-1225

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