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

Tetsu-to-Hagané Vol. 72 (1986), No. 3

  • Report of Symposium on “Physical Chemistry and Process Engineering of Steelmaking Reactions”

    pp. 347-352

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  • Defect Chemistry of Iron Oxides and Its Relevance to the Reduction of Iron Ores in Blast Furnace

    pp. 353-360

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  • Present and Future of the Research on High Purity Iron

    pp. 361-367

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  • Recent Status of Cold Plasma Utilization

    pp. 368-372

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  • Current and Future in Diffusion Welding

    pp. 373-379

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  • Mathematical Modelling for Process of Direct Reduction of Iron Ore by Rotary Kiln

    pp. 380-387

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    A mathematical model for the process of direct reduction of iron ore (DRI Process) by rotary kiln has been developed to predict the axial distribution of process variables for Case 1 (i.e., the case with the feedings of auxiliary air and carbonaceous materials along the axis of the kiln) and for Case 2 (i.e., the case without these feedings).
    Direct reduction of hematite by solid carbon, combustion of coal or coke in the solid bed, combustion of heavy oil in the freeboard which is fed from burner and combustion of CO evolved from the bed are taken into account together with the heat and mass transfer processes.
    Applicability of the model has been verified by comparison of the calculated results of fractional reduction or solid-bed temperature with the experimental results obtained by the other investigators. The model has been applied to investigate the effects of the flow-rate ratio of solid to gas and that of carbon to ore on the axial distribution of process variables.
  • Analysis of Retardation Phenomenon in Iron Ore Reduction by Three-Interface Model with Solid-State Diffusion Step

    pp. 388-395

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    In order to investigate the retardation phenomenon in iron ore reduction, fine ore particles were reduced with Hydrogen gas in the temperature range from 650°C to 850°C by microbalance technique. Many unreacted wüstite particles, of which diameter is 0.58 μm-0.76 μm, surrounded by dense iron were micrographically observed in a sponge iron. Three-interface model combined in series with solid-state diffusion step can simulate very well reduction curve involving retardation period. Permeability of oxygen obtained by parameter-fitting method is in the range of 5.3×10-14g/cm s-1.6×10-12 g/cm s at 650°C-850°C, which results coincide with previously reported data within a range of one order.
  • Reduction Kinetics of Synthetic Chromite Pellet with Hydrogen

    pp. 396-402

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    Experiments have been made of the reduction of synthetic FeCr2O4 pellet with hydrogen in a temperature range from 800°C to 1 300°C. The reduction of FeO component preceded that of Cr2O3, and it proceeded topochemically under the formation of relatively clear interface between reduced shell (γ-Fe+Cr2O3) and unreacted core. In the reduction stage of Cr2O3 component, the reaction interface was considerably widely. diffused. Kinetic analysis based on an unreacted core model was conducted with the reduction stage of FeO component, and the rate constant of chemical reaction kr and the intraparticle diffusivity De were evaluated. The activation energy of the chemical reaction was about 30 kcal/mol. The temperature-dependency of De was very strong, especially at temperatures above 1 200°C.
  • Flow Characteristics of Gas and Fine Particles in Packed Bed

    pp. 403-410

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    A cold model experiment and a theoretical study concerning the two phase flow of gas and solid in a packed bed were performed and the following results were obtained.
    1) Pressure drop and powder hold-up increased with the decrease in gas velosity when gas velocity was below a certain value.
    2) A theoretical model to predict the pressure drop and the powder hold-up was developed under the assumption that the interaction force between gas and powders was expressed by the Ergun type gas flow resistance.
    3) On the basis of this model, the aggravation of gas flow resistance of the blast furnace under the conditions of reduced production rate was explained to be caused by the accumulation of powders in the lower part, above tuyere level, of the furnace.
  • Effects of Various Factors on the Local Corrosion of Blust Furnace Trough Material at the Slag-Metal Interface

    pp. 411-418

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    An investigation has been made on local corrosion rate of clay-bonded SiC specimen at the CaO-Al2O3-SiO2 slag-liquid iron alloy interface. The local corrosion rate increases linearly with increasing dipping time. The corrosion rate is negligible small in the melt saturated with carbon and increases markedly with decreasing carbon concentration. After reaching maximum, it decreases slightly with further decreasing the carbon concentration. The corrosion rate increases with increasing temperature and number of revolution of the specimen. Aluminum addition to the metal increases markedly the corrosion rate, while silicon addition decreases it. The local corrosion does not proceed in carbon-saturated iron, but proceeds rapidly by an addition of aluminum to the metal or by rotating the specimen. The corrosion rate increases remarkably with decrease in SiO2 concentration in the lower carbon concentration range of the metal. These behaviors of the corrosion rate are explained by the mechanism that the local corrosion is caused by the active motion of a thin slag film between specimen and metal phase induced by Marangoni effect and by CO bubbles evolved at slag film-metal interface. The main rate determining step is estimated to be the removing process of the following corroded products, that is, carbon particles in the slag film produced by oxidation of SiC in near the saturated carbon concentration and the clay dissolved from specimen into the film in the lower carbon concentration range.
  • Rate of Nitrogen Desorption from Molten Iron by Ar Gas Injection

    pp. 419-425

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    A study was made on the rate of nitrogen desorption from molten iron by argon gas injection. Argon was injected into the melt through an submerged alumina nozzle of 0.1cm in I.D. and 0.3cm in O.D. The immersion depth of the nozzle was 4.65.2cm. The gas flow rate was 7496 Ncm3/min. The oxygen contents in the melt were varied from 0.004 to 0.066%. During the experiment, the bubble formation time was measured by using a pressure pulse technique.
    The measured desorption rates are compared with those calculated by a mixed control model considering mass transfers in both liquid and gas phases and chemical reaction at the bubble-metal interface. Nitrogen desorption during bubble formation is taken into account in the model. From the comparison between calculation and experiment, the chemical reaction rate constant was obtained. It is shown that the chemical reaction rate constant decreases with increasing [%O] + [%S]/2. The rate constant obtained in the present study agrees well with that in the previous study of nitrogen absorption in molten iron. It was confirmed that both nitrogen absorption and desorption in molten iron could be explained by the mixed control model.
  • Effect of Densities of Gas and Liquid on Behavior of Injected Gas in the Initial Jet Formation Zone

    pp. 426-433

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    Studies have been made on physical interactions between injected gas and liquid exclusively in the initial jet formation zone. Helium or nitrogen gas was injected into the water bath through an orifice of 0.2-0.4cm in diameter located at the bottom. The jet behavior was observed directly by using a high speed cinecamera. Pressure at the orifice exit was measured by a pressure transducer.
    The bubbling-jetting transition was found to occur, irrespective of the densities of gas and liquid, when the linear velocity of gas reached the sonic velocity at the orifice exit. The transition occurred more abruptly with increasing the density ratio of gas to liquid. The bubbling behavior was characterized quantitatively by analyzing linkage and severance of gas jets. Densities of gas and liquid were found to have a large effect on the bubbling behavior. On the basis of the observation of the jet expansion at the orifice exit and continuity of bubbles, apparently different views on gas jet characteristics advanced by previous investigators could be reconciled. It was confirmed that the submerged gas jet attaining a sonic flow at the orifice exit forms a supersonic jet inside the liquid phase by the pressure measurements.
  • The Development of Technology for Decarburization of Pre-refined Hot Metal in BOF

    pp. 434-441

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    A method by combination of soft-blow with oxygen bottom blowing (CS-OB method) which is suitable for decarburization of desiliconized, dephoshorized and desulphurrized (pre-refined) hot metal in BOF has been developed. Its blowing condition had to be decided to increase the Fe yield. The Fe yield in the decarburization of pre-refined hot metal was mainly affected by spitting and Fe oxidation since the decarburization was carried out with small amount of slag. The CS-OB method was characterized by the combination of extremely soft top blowing with bottom gas stirring to decrease both spitting and Fe oxidation at the same time.
    The most suitable condition found in the 0.5t/ch lab. test and the 100t/ch BOF test was L/L0=0.10.2, the bottom gas flow rate=0.20.25 Nm3/t·min.
    Oxygen used for the post combustion of CO gas in the furnace increased by soft blowing in the CS-OB method. Heat efficiency of the post combustion was estimated about 90% in the 100t/ch BOF test.
    x

    Readers Who Read This Article Also Read

    1. Theoretical Study on Gas Flow and Heat and Mass Transfer in a Converter Tetsu-to-Hagané Vol.75(1989), No.3
    2. A Model Study on Jet Penetration and Slopping in the LD Converter Tetsu-to-Hagané Vol.58(1972), No.1
  • Relationship between Characteristics of Hollow Shells and Plug Shapes in Press Roll Piercing

    pp. 442-449

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    Influence of plug shape on surface properties of hollow shell and on plug life was investigated on a press roll piercing (PRP) test mill by piercing test billets with artificial defect. Tool shape had an effect on tool life. Plugs with a sharp head (C type) had a poorer life than those with a head of egg bottom shape (N type). Hollow shells pierced by N type plug showed good surface qualities on outer and inner surface. Stable loads in piercing process were observed by using N type plug. However, mandrel thrust load by N type plug was larger than that by sharp head plugs. As far as porosity defects in a CC-billet were concerned, it was observed that the larger the radius of curvature of plug tip became, the more reduction in defects was attained due to forging effect. Additionally, the relationship between metal flow and plug shape in PRP process was explained by experimental results.
  • Surface Behavior and Temperature of Plug in Piercing of Seamless Steel Pipe

    pp. 450-457

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    Prediction of tool temperature is very important to improve its life, since tool life is strongly influenced by increase in temperature of tool surface in piercing and rolling process of seamless steel pipes. The temperature of plugs under some piercing conditions of cross roll and press roll piercers was calculated. Actual temperature of plugs were measured and compared with the calculated results to confirm the validity of calculation. In addition, thin layer of actual plug surface after piercing campaign was extracted by solvent method and structure of the thin layer was observed by using an electron microscope. It was clarified that temperature of plug surface becames over 1 200°C in piercing and that a metallic surface plugs were unsuitable for a piercer. Black scale film on plug surface showed a good protective effect against heat conduction. Temperature of a plug treated with scale film became from 700°C to 800°C in piercing. The black scale film on plug surface under piercing condition was enriched in SiO2 and it was presumed that the surface of plug was covered with a thin layer of melted scale, namely, scale lubricant. An amorphous thin layer was confirmed on the surface of a plug after piercing campaign through observation by electron microscope and electron diffraction patterns of the extracted thin layer.
  • Effect of Combined Addition of Niobium and Boron on Thermomechanically Processed Steel

    pp. 458-465

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    In the thermomechanical control process (TMCP) with accelerated cooling, the effect of the combined addition of boron with a grain-refining element, niobium, vanadium or titanium, on the mechanical properties and microstructures of low-carbon steels was studied. It was found that although the single addition of boron has little effect on the steel properties, the combined niobium-boron addition conspicuously improves the strength and toughness balance. In the case of the single addition of boron, coarse Fe23(CB)6 precipitates at γ-grain boundaries after rolling, and the γ-α transformation suppressing effect by boron is remarkably weakened. Niobium addition to boron steel has the effect of suppressing the precipitation of Fe23(CB)6 and strongly retards the γ-α transformation, and hence produces a fine-grained bainitic structure. Titanium has the same effect as that of niobium, but vanadium does not. The strengthening and toughening mechanism of steels by the combined niobium-boron addition was also discussed by examining the effect of alloying elements on the recrystallization stop temperature of γ during rolling, γ-α transformation behavior and so on.
  • Effect of Composition and Processing Variables on Thermomechanically Processed Niobium-Boron Steel

    pp. 466-473

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    In the thermomechanical control process (TMCP) with accelerated cooling, the effect of composition and processing variables on the mechanical properties and microstructure of niobium-boron steel was studied. It was clarified that in order to achieve a good strength and toughness balance by the combined addition of niobium and boron, it is necessary to lower the carbon content, to dissolve niobium during slab-reheating and to controlled-roll with sufficient reduction in the non-recrystallization region γ. With these conditions, a fine-grained bainitic structure is obtained. The change of the mechanical properties and microstructure of niobium-boron steel with composition and processing variables can be explained in terms of the behavior of boron and the amount of niobium in solution. The strength and toughness controlling factors of niobium-boron steel were also discussed.
  • The Effect of Stress on Degradation of 1Cr-1Mo-1/4V Steel at Elevated Temperatures

    pp. 474-481

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    The creep tests for the specimens aged and stress-aged in the temperature range from 550 to 700°C have been carried out at 550°C-28 kgf/mm2 to determine quantitatively the degree of degradation of a 1Cr-1Mo-1/4V steel. The decrease in creep resistance due to aging has been discussed in terms of two microstructural changes: (i) a homogeneous change; the coarsening of intragranular carbides, and (ii) a heterogeneous change; the formation of subgrains or ferrite grains along prior austenite grain boundaries.
    When the stress-aged specimens were compared with the specimens aged without stress at the same hardness level, the creep resistance of the former was substantially lower than that of the latter and the amount of subgrains or ferrite grains for the former was significantly greater than that for the latter. The decrease in the creep resistance was proportional to the increase in the width of recovered area, which was defined as a parameter representing the amount of subgrains or ferrite grains along the prior austenite grain boundaries.
    The loss of the creep resistance during elevated temperature exposure is caused not by the homogeneous microstructural change of the carbide coarsening, but by the marked local recovery along the prior austenite grain boundaries.
  • Dynamic Recrystallization in High Temperature Torsional Deformation of Low Carbon Steel and Vanadium-Microalloyed Steel

    pp. 482-488

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    Low carbon steel and vanadium-microalloyed steel were deformed by torsion in the temperature range from 900° to 1 200°C and the strain rate range about 10-3 to 10s-1.
    A characteristic type of deformation with dynamic recrystallization, which has either single or multiple peaks in the stress-strain curve, was observed in both steels under all the experimental conditions. The dynamic recrystallization behavior was analyzed with a special emphasis on the transition from multiple to single peak deformation. The size of the dynamically recrystallized grain was also measured. It was able to be presented as a function of ZENER-HOLLOMON parameter, Z, and it did not exhibit any dependences on the initial grain size.
    The condition for transition of the deformation behavior was investigated in detail from the following two view points (i) effect of the relative magnitude of the critical strains for recrystallization on the transition behavior, and (ii) effect of the initial grain size on the transition.
    x

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    1. Dynamic Recrystallization of Austenite in 18-8 Stainless Steel and 18 Ni Maraging Steel and Its Related Phenomena Tetsu-to-Hagané Vol.66(1980), No.12
  • Effect of Ti and Si on Precipitation Hardening of Martensitic Stainless Steel

    pp. 489-496

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    The effects of Ti and Si on the age-hardening response and ductility after aging were studied for low C, N-14Cr-7Ni martensitic stainless steel, and the main results obtained are as follows:
    (1) The age-hardening response of steels containing Ti singly is dependent on the logarithm of effective Ti contents ([Ti]) and the effect of [Ti] is almost the same as that in Fe-18Ni alloy.
    (2) While the age-hardening response of steels containing Si alone is small, that of steels containing Ti in the presence of more than 2 at% Si is very large. In this case, the effects of [Ti] and Si on the equal age-hardening response are dependent on the value of ln[Ti]6Si7. This can be explained by the solubility of G phase (Ni16Ti6Si7) in matrix.
    (3) In the steels containing both Ti and Si, the age-hardening rate is controlled by the super saturation of G phase.
    (4) A higher ductility of steels can be attained at higher strength level by combined additions of Ti and Si than by single addition of Ti. This is explained by the fact that in the latter steels δ phases (Ni3Ti) precipitate easily along grain boundaries and intergranular fractures occur at lower stress level.
  • 良い英文を書くために

    pp. 519-521

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  • “ですね症候群”

    pp. 521-521

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  • 抄録

    pp. 531-534

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