Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 72 (1986), No. 7

  • A Concept of Life and Remaining Life Prediction of High Temperature Structural Materials Based on the Characteristics of Creep-Fatigue Crack Propagation

    pp. 711-719

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  • Defect Chemistry of Iron Oxides and Its Relevance to the Reduction of Iron Ores Blast Furnace (2)

    pp. 720-731

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  • Properties Required for Axis and Wheel of Railway Rolling Stocks

    pp. 732-739

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  • Patent Specification

    pp. 740-746

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  • Effects of Purification on Fracture Toughness of Steels

    pp. 747-758

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  • Countercurrent Reduction of Iron Ore Particles by Fluidized Rotary Bed with Drum Type Reactors

    pp. 759-766

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    Fine iron ore particles were countercurrently reduced with hydrogen gas at 750°C by fluidized rotary bed in order to pursue the potentiality of the fluidized bed process in direct reduction processes.
    As the fluidized rotary bed is established only by balancing centrifugal force applied to the ore particles with gravity, it is independent of gas flow rate. Therefore, countercurrent operation of ore and gas can be easily obtained.
    In this experiment, three kinds of reactor (i.e. drum type reactor, conical type reactor, L/D reactor) were used for the purpose of obtainning basic data. Gas utilization coefficient attained with these reactors increases with the increase of stage number or L/D value and exceeds equilibrium value (Fe/FeO) even if in high fractional reduction, which means countercurrent reduction should be established.
    Thus, for the purpose of evaluation of this effect, mixing behavior of ore particles was studied by impulse response method in the cold state. Obtained internal age distribution curve has a tendency of shifting from complete mixing flow to plug flow with the increase of the stage number or L/D value, which results coincide with the estimation inferred from the countercurrent reduction test.
  • Analysis of Fluidized Rotary Bed in Countercurrent Reduction by Three-Interface Model

    pp. 767-774

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    Countercurrent reduction results by fluidized rotary bed have shown that gas utilization increased with the increase of the stage number or L/D value, which meant the countercurrent reduction should be established.
    However, since the mean residence time of are measured was not equal and the countercurrent effect was different in each reactor, both the mean residence time factor and the countercurrent factor affect simultaneously the fractional reduction.
    Thus, in this paper, in order to investigate only the effect of countercurrent on the fractional reduction, a single fluidized-bed-model including gas and are flow in the bed was developed with three-interface model and numerical computation was conducted for the three-staged reduction.
    Under the assumption that gas flow is plug flow and are is complete mixing flow in a one-staged bed, fractional reductions computed from this model were in good agreement with observed one in each reactor.
    Therefore the effect of countercurrent on the fractional reduction was estimated separately by this model.
  • Experimental Study on the Relation between Microstructures of Constituent Minerals and Pores and Reducibility of Sinter

    pp. 775-782

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    Effects of the microstructures of constituent minerals and pores on the reducibility of sinter were investigated by using six kinds of sinter having different basicity.
    1) The reducibility of small particle sinters (0.8 mm in dia.) which contain few macro-pores increases with an increase in basicity and has a good correlation with the microstructure of the sinters. Sinters which are mainly composed of hematite and calcium ferrite are reduced much faster than sinters mainly composed of magnetite and slag.
    2) The reducibility of sinters of spherical form (12 mm in dia.) is not necessarily correlated with the basicity but is definitely affected by the porosity of the sinters, especially by the content of macro-pores.
    3) It is concluded from these findings that the intrinsic reducibility of a sinter is determined by the microstructures of constituent minerals and micro-pores but that the macro-pores which supply reducing gas to each mineral grain also play an important role in determining the overall reducibility of the sinter.
  • Influence of Coke Layer Collapse Phenomenon on Burden Distribution at the Top of Blast Furnace

    pp. 783-790

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    The phenomenon of coke layer-collapse occurs when ore is dumped onto the inclined coke bed. The coke layer-collapse causes to change the distribution of ore and coke layer thickness in the radial direction. Therefore, the effects of charging condition and distribution of gas flow and burden descending velocity on the coke layer-collapse have been studied by using a reduced-size experimental apparatus in which the conditions of gas flow and burden descent have been simulated to those of actual furnace top.
    The experimental results show that the magnitude of coke layer-collapse is mainly dominated by the charging mode, and the state of coke stacking in the central region after the collapse is also influenced by gas flow and descending velocity distribution. The changes in inclination angle of coke layer and coke movement accompanied by the collapse have been investigated. It is confirmed from these investigations, that the scale of coke layer-collapse depends on the stability of inclined coke layer. On the base of these findings, a mathematical model for quantitative evaluation of coke layer-collapse is developed by introducing the theory of soil mechanics. The calculated results by the model consist with experimental results for coke layer-collapse.
  • Reexamination of the High Temperature Region of Fe-W Binary Alloy Phase Diagram

    pp. 791-798

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    High temperature region of Fe-W binary alloy phase diagram was reexamined by ion intensity thermal analysis with a Knudsen cell-mass spectrometer combination and metallographic method. Temperature of two invariant reactions, Fe(α) Fe3W2(ε) and Fe3W2(ε)=L+(W) and composition of the decomposing phases were determined through the arrest temperature and the duration of the arrest appearing on the heating curves of the ion intensity. Identification and composition determination of the equilibrating phases were also carried out by metallographic examination of diffusion couples and heat treated samples.
    Obtained results agreed well with some phase diagrams in the literatures. FeW (σ) phase which was claimed to exist in a phase diagram in a literature was not detected in the experimental temperature range. This coincides with the behavior of the activity curves of Fe-W alloys reported by the authors previously.
    The results of this study prove the ion intensity thermal analysis to be useful for the study of high temperature transformations including liquid phase.
  • Deformation and Recrystallization Behavior of Ferritic Stainless Steel in High Speed Hot Rolling

    pp. 799-806

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    The recrystallization behavior of ferritic stainless steel in high speed hot rolling has been investigated in relation to the strain distribution through the thickness of the rolled strip. The strip of which the size was 2×20×430 mm was rolled at the temperatures from 900°C to 1050°C and at the rolling speed of 20 m/s with or without lubrication. The rolled specimen was quenched in water at the interval of 25 ms after rolling. The redundant shear strain caused by friction forms severely sheared region beneath the surface with the thickness of about 100μm. The maximum equivalent strain εmax in severely sheared region reaches about 4 times of compressive strain and εmax in rolling without lubrication, is always larger than that in lubricated rolling.
    Extremely fine recrystallized grains are formed in severely sheared region when εmax exceed a critical value, which is dependent on ZENER-HOLLOMON parameter Zmax in severely sheared region and independent of lubrication condition. The size of the recrystallized grain is also strongly dependent on Zmax.
    From these results and optical micrographs, it is concluded that the recrystallized grains observed in this study are statically recrystallized ones.
  • Saw-toothed Chip Formation and Chattering Vibration on the Machining of Bearing Steel in Supercooled Austenitic State

    pp. 807-814

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    A new machining process, called auscutting, has been developed, in which the cutting operation is performed in supercooled austenitic state during quenching. In auscutting, the saw-toothed chip is formed and the chattering vibration occurs under some cutting conditions. In this paper, the relation between the chattering vibration and the periodic chip formation is investigated. The formation mechanism of the saw-toothed chip is considered by observing the micro structure of the surface of chips.
    The results obtained are summarized as follows :
    (1) The frequency of the chip formation is varied with cutting conditions. It increases with the increase of cutting speed, but decreases with the increase of depth of cut and feed.
    (2) The micro slips occur continuously in the case of flow type chips. The cracks generate on the chip surface without the micro slips in the case of saw-toothed chips, when the shear strain exceeds a critical value.
  • Workability and Static Recrystallization of Powder-Consolidated Nickel-Base Superalloy Mod. IN-100

    pp. 815-822

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    There is a limit to rolling of Ni-base superalloy IN-100 at the temperature range room temperature1 250°C because of about 60% γ' volume fraction.
    In a series of our experiments, however, it was shown that powder-consolidated Mod. IN-100 by hot isostatic pressing could be rolled at the temperature range 850950°C. Tests were carried out with powder-consolidated Mod. IN-100 to make clear quantitatively the effects of rolling reduction, annealing temperature and annealing time on the recrystallization. Furthermore, it was shown that Mod. IN-100 as powder-consolidated was possible to become superplastic and its total elongation exceeded 300% over a suitable range of temperature and strain rate.
  • A Kinetics Model for Carbide Precipitation during Over-aging in Continuous Annealing of Low-carbon, Cold-rolled Sheet Steels

    pp. 823-830

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    Rapid-cooling and over-aging treatment just after recrystallization annealing is necessary to continuous annealing for low-carbon, cold-rolled sheet steels to prevent carbon aging of the products. In this paper, a theoretical model for carbide precipitation kinetics during this stage has been derived. The model involves two rate processes, the one being precipitation to ferrite grain boundaries, and the other within grains. As the latter one, the model expresses nucleation and growth, and besides, heterogeneous nucleation on manganese sulfides.
    This model has only one adjusting parameter which was decided experimentally. Nevertheless, one can calculate decay of solute carbon in various cases including such cases that temperature varies.
    In order to prove this theory available, an experiment of quench aging using commercially produced. low-carbon steel was conducted. Results of theoretical calculation have good agreement with the experimental results, although the theoretical precipitation rate is slightly slower at early stage, and slightly faster at late stage than the experimental value. Arrhenius plotting of the experimental data showing no simple linearity against the inverse of temperature, represents the phenomenon complicated.
    Differences between the present theory and the previous ones were discussed.
  • Theoretical Analysis of Grain Boundary Carbide Precipitation in Stainless Steels

    pp. 831-838

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    It has been well-known that grain boundary carbide precipitation in ferritic stainless steels is faster than that in austenitic ones. However, there were few theoretical studies for this problem compared with that of austenitic ones. The aim of this study is to formulate the thermodynamic data such as activities of Cr and as the formation energies of carbides from many references and to compose a carbide precipitation model based on local equilibrium and diffusion control.
    Amounts and compositions of precipitated carbides and Cr contents near grain boundaries were calculated from model and were in good agreement with the experimental data. TTS (Time-Temperature-Sensitization) diagrams were evaluated by calculating Cr content near the grain boundaries and the amounts of total precipitates. The sensitization of a 0.01%C ferritic stainless steel became 105 times as rapid as that of a 0.03%C austenitic ones.
  • Effect of Precipitation Behaviour of Intermetallic Compounds on Strength and Toughness of Maraging Steels

    pp. 839-846

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    Precipitation behaviour of intermetallic compounds is one of the important factors which control the strength and toughness of maraging steels. However, systematic investigations on the precipitation behaviour have hardly carried out.
    In the present paper, the effect of alloy series (Ni-Co-Ti, Ni-Co-Mo and Ni-Co-Mo-Ti steels) with the variation of nickel content on the strength and toughness was studied. Precipitation behaviour of intermetallic compounds was identified by non-aqueous electrolyte extraction method and transmission electron microscopy. Further, the relation between fracture pattern and the precipitation behaviour was investigated in the alloy series with various toughness levels. Results are summerized as follows:
    1) Titanium containing steels showed the marked decrease in toughness due to the grain boundary and lath boundary precipitates of η-Ni3Ti.
    2) Molybdenum containing steels showed the highest toughness level with wide range of nickel contents due to the finely dispersed precipitates of σ-FeMo in the grain.
    3) Molybdenum and titanium containing steels including 18% nickel commercial steels showed the highest tensile strength level due to the multi-precipitations of η-Ni3Ti, σ-FeMo and Ni3Mo. It was ascertained that the addition of molybdenum and the increase in nickel content suppressed the grain boundary and lath boundary precipitates of η-Ni3Ti and resulted in the highest toughness level.
  • Stress Corrosion Cracking of Mild Steel in Coal Gas Liquid

    pp. 847-854

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    Field reproduction of intergranular stress corrosion cracking (IGSCC) through two year exposure test in coal gas transport lines using U-bend specimens and laboratory reproduction of IGSCC were carried out in order to clarify the effects of environmental factors such as electrode potential, pH and temperature on crack initiation and propagation.
    1) IGSCC of mild steel was reproduced by field exposure test in coal gas transport line. Cracks initiated at corrosion pits within crevices.
    2) The critical depth of corrosion pits for IGSCC initiation was estimated about 70 μm by the application of the extreme value analysis.
    3) The possible cracking region was assessed based on the high-and low potential sweep rates polarization curves and stability of the corrosion products as indicated by the potential/pH diagram.
    4) Degradation of mild steel in the coal gas liquid was classified into four regions:
    I) HE region (TGSCC): less noble than -1 000 mV vs S.C.E.
    II) SCC region(IGSCC): -700- 500 mV vs S.C.E.
    III) Fissure region (TG):-550-500mV vs S.C.E.
    IV) General corrosion region : more noble than- 500 mV vs S.C.E.
  • Effect of Hardness of Steels and Welds on Liquid Metal Embrittlement Cracking in Molten Zinc

    pp. 855-861

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    Liquid metal embrittlement cracking (LMEC) of steels and welds in hot dip galvanizing process was studied. Commercial weldable structural steels were exposed to Y-Groove cracking test and sustained load test in molten zinc, and the effect of metallugical properties on LMEC sensitivity and fracture stress were investigated.
    Results obtained are summarized as follows.
    (1) In both tests the welds suffered from intergranular fracture in grain coarsed region of heat affected zone in molten zinc. This behavior corresponds to LMEC of welded steel structures.
    (2) LMEC sensitivity of steels and welds, which is expressed by cracking percentage in Y-Groove Cracking Test or liquid zinc embrittlement fracture ratio in Sustained Load Test, is influenced by hardness.
    (3) LMEC fracture stress is affected by hardness and grain size of steels and welds.
  • Calculation of the Equilibrium Phase Diagram of the Ni-Cr-W Ternary System

    pp. 862-869

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    A computer calculation was carried out to construct an equilibrium phase diagram of a Ni-Cr-W ternary system between 800 and 1700°C, on the basis of the experimentally determined phase equilibria between 1000 and 1200°C. The method developed by Kaufman and his collaborators was employed in the present calculation. Only sub-regular solution parameters of the three binary systems were used to describe the excess free energy of ternary solution phases such as liquid and three terminal solid solutions: nickel-rich fcc γ, chromium-rich bcc α1 and tungsten-rich bcc α2 phase. No ternary term was added to the excess free energy expression. The sub-regular solution parameters of fcc solid solution in the Cr-W binary system were determined to be gfccCr-W=hfccCr-W=9 000 cal/g-at. A line compound approximation was employed to describe the free energy of intermetallic compounds such as σ phase and β phase (Ni4W). The previously reported line compound parameter of σ phase in the Ni-Cr binary system was revised in addition to the determination of the σ phase parameter in the Ni-W binary system.
  • Comparison between the Calculated and the Experimentally Determined Phase Diagrams in the Ni-Cr-W Ternary System

    pp. 870-877

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    A calculated equilibrium phase diagram of the Ni-Cr-W ternary system was critically compared with experimentally determined phase diagrams. Although some of the parameters for the phase diagram calculation were determined from the phase equilibria between 1000 and 1200°C, the calculation was proved to form a good estimate of the phase equilibria between 800 and 1 600°C. Several predicted reactions from the calculation were confirmed by experiments. They were a ternary eutectoid reaction:σ-γ+α12, and two eutectic reactions: L→γ+σ and L→γ+α1, where L indicates liquid and γ, α1and α2 stand for nickel-rich fcc, chromium-rich bcc and tungsten-rich bcc terminal solid solution phase, respectively.
  • 良い英文を書くために

    pp. 878-879

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  • 抄録

    pp. 886-887

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  • 今こそ基礎研究を

    pp. 888-888

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