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

Tetsu-to-Hagané Vol. 73 (1987), No. 8

  • The Recent Trend of Research and Development on High Temperature Gas-cooled Reactor

    pp. 917-922

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  • Comparison of Japanese and Western Refractory Technologies for Steelmaking Based on the IISI Report

    pp. 923-930

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  • Microwave Melting Method

    pp. 931-935

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  • Advancement of Control for Marine Biofouling

    pp. 936-946

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  • Oxygen in Silicon

    pp. 947-955

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  • Mineral Forming and Its Composition Model for Iron Ore Sinter

    pp. 956-963

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    The minerals and their composition of iron ore fluxed sinter are important factors on sinter qualities as the constituent of the matrix. The present work was carried out to predict the produced sinter mineral composition (hematite, magnetite, calcium ferrite and slag) prior to sintering with the use of material imformation. On the composition of sinter minerals, hematite and magnetite are determined with the iron oxide form and coke content in mix, and calcium ferrite and slag are influenced by SiO2 and Al2O3 in mix. The model prediction was in relatively good agreement with the observed values by quantitative X-ray diffraction analysis.
  • Strength Controlling Factors and Their Model for Iron Ore Sinter

    pp. 964-971

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    Strength is the basic characteristic of sinter manufactured by the agglomeration process. A fundamental study was carried out for the analysis of the controlling factors of sinter strength and a quantitative prediction model for sinter strength was developed. Sinter strength was described in terms of the porosity, the mineral composition and the melting ratio of sinter on the basis of the strength model of the porous materials. The calculated strength by the model was in relatively good agreement with the observed one on the various sinter.
  • Reduction Rate of Wustite Pellets with CO-H2 Gas Mixtures

    pp. 972-979

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    A mathematical model for the kinetics of reduction of porous wustite pellets with CO-H2 gas mixtures was developed on the basis of the unreacted-core model. In this model, (1) the water-gas shift reaction with reduced iron as catalyst was taken into consideration, and (2) the diffusion rates of gases through the gasfilm and the product iron layer were evaluated using the Stefan-Maxwell equations for multi-component gas diffusion. Porous wustite pellets were reduced with CO-H2 gas mixtures(5Nl/min) at 900°C, and experimental data obtained were analyzed by the model. The results were as follows:
    (1) The effect of the water-gas shift reaction on the reduction kinetics was negligibly small.
    (2) Relation between the reduction rate and bulk gas composition showed negative deviation from linearity. It was due to the dominant contribution of diffusional resistances through the product layer to the overall reaction rate.
    (3) The values of rate parameters in the model varied with bulk gas composition. When bulk gas composition was constant, however, the effects of the changes of gas composition within the pellet during reduction on the values of the parameters were negligibly small, and therefore the values can be treated as constants.
  • Reduction Behavior in Cohesive Layer of Blast Furnace

    pp. 980-987

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    Behavior of gas flow, heat transfer and reduction of iron ore in a cohesive layer is investigated by the non-steady mathematical model and experiments.
    It was found that
    1) reduction of iron ore in a cohesive layer is affected by the gas flow resistance through the cohesive layer,
    2) with the increase of the gas flow resistance through the cohesive layer, rate controlling step of heat transfer and reduction in a cohesive layer is switched over from the convection to the diffusion,
    3) the reduction of iron ore in a cohesive layer proceeded from the surface to the center of the cohesive layer.
  • Phosphorus Distribution between MgO-saturated Na2O-FetO-SiO2-P2O5 Melts or CaO-saturated FetO-SiO2-P2O5 Melts and Molten Iron

    pp. 988-995

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    In order to meet the recent demand for low phosphorus steels, highly basic slags must be used to increase the refining efficiency. The purpose of this study is to obtain the information of the thermo-dynamic property of phosphorus in basic slag melts.
    In this study, the equilibrium distribution ratio of phosphorus (LP) between MgO-saturated Na2O(-CaO)-FetO-SiO2-P2O5 slags and molten iron was measured as a function of temperature, slag composition and pertial pressure of oxygen. As a result, the CaO equivalent of Na2O in basicity was found to be 2.3 in terms of mole fraction.
    Since CaO-saturated FetO-SiO2-P2O5 slags are also expected to have great capacity of dephosphorization, the distribution ratio of phosphorus between slags and molten iron was measured at 1600°C together with the influence of additional Na2O or MgO on the phosphorus distribution. As expected, both components did slightly enhance dephosphorization within the concentration range used in this study.
  • Cooling Characteristics of Steel Sheet by Water Film in Hot Strip Mill

    pp. 996-1003

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    For an examination of cooling characteristics of hot steel sheets cooled by water films, tests were conducted on a model cooling apparatus and an actual run-out table in the hot strip mill at Kobe Steel's Kakogawa Works and led to the following conclusions:
    (1) Cooling capacity along a “stagnation line” created by the water film is nearly constant at a water flow rate of 0.3 to 0.9m3/min·m.
    (2) Cooling capacity of “stagnation region” is reduced by “mixing region” that exists near the water film.
    (3) At a steel temperature range of 750-800°C, the effects of nozzle height and slit gap on cooling capacity are negligible.
    (4) Cooling tests of high temperature steel (730-860°C) on the run-out table demonstrate no difference in cooling capacity between this method, which uses water films, and the conventional one which uses water bars.
  • Effects of Zinc Phosphating on Anti-cratering Properties of Steel Sheets in Electrodeposition Coatings

    pp. 1004-1009

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    Effects of zinc phosphating on the cratering phenomena during cathodic electrodeposition coating were studied. Cold rolled(CR), electrogalvanized(EG), double-layer zinc-iron electroplated (Zn-Fe) and galvannealed sheet(GA) were used as test materials. The voltage applied between the anode and the cathode in a plating solution was increased at a constant rate from zero to a certain value (200 to 400 V), and then kept constant. Two peaks were observed in the change of the current with time in the coating process. The peak current ratio, iB (second peak)/ iA(first peak), correlated to the crater density. Phosphate treatment increased the crater density and brought about a high peak current ratio. This tendency was the most remarkable on GA. For all kinds of steel sheets both the value of iA and iA/V(voltage) were decreased by phosphating. The electric resistance calculated from the current-time relation did not depend on the materials.
  • Characteristics of HAZ Microstructure in Ti-B Treated Steel for Large Heat Input Welding

    pp. 1010-1017

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    Recently the needs for 50 kgf/mm2 tensile strength steels with good HAZ toughness under the welding condition of large heat input have been increasing. A new type of 50 kgf/mm2 tensile strength steel containing small amounts of Ti and B was developed for this purpose.
    The steel is charactarized by the microstructure in the HAZ which consists mainly of the intragranular ferrite plates(IFP) without the high carbon martensite islands and the small amount of the grain boundary allotriomorphs.
    The toughness of IFP is very good due to its fine ferrite grain. Complex precipitates of TiN-MnS-Fe23(CB)6 act as nuclei of IFP and B addition suppresses the growth of grain boundary allotriomorphs. The authors suppose a mechanism that a carbon depleted zone formed around Fe23(CB)6 assists ferrite nucleation as the reason why IFP is produced effectively by these complex precipitates.
  • Effects of Metallurgical Factors on Toughness of Flash Welded Joint of Sheet Steel

    pp. 1018-1025

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    The effects of metallurgical factors such as elongated inclusions, microstructure, and hardness across the welded interface on the toughness of flash welded joint were studied.
    As upset distance increased, microstructure changed from bainitic ferrite to fine polygonal ferrite, and Charpy impact properties such as vTre and vEs of welded joint deteriorated remarkably. This deterioration was mainly caused by the elongated inclusions which were affected by the inclusions in base metal and upset distance. The effects of microstructure, hardness and (200) texture at the welded joint on the toughness were smaller than the effect of inclusion.
    It was concluded that the decrease of inclusion in base metal and the decrease of hardness of welded joint by the control of upset distance were essential for the improvement of toughness of welded joint.
  • A Kinetic Model for Phase Transformations of Low Carbon Steels during Continuous Cooling

    pp. 1026-1033

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    A calculation model for predicting the progress of transformations of low carbon steels during continuous cooling and the microstructure after cooling has been developed. In this model, the progress of tranformations is assumed as follows. The transformation from austenite to ferrite starts at the equilibrium temperature, Ae3. The ferrite transformation follows 'nucleation and growth' model at the early stage and then follows 'site saturation' model at the later stage. The carbon content of the untransformed austenite increases with the progress of ferrite transformation. The pearlite transformation starts when the carbon content of the austenite reaches the extrapolated Acm line in the equilibrium diagram. The bainite transformation starts when the temperature reaches the bainite-start temperature, Bs, which is experimentally determined. Besides, the effect of chemical composition on the transformation kinetics are taken into consideration by using the theoretically calculated nucleation rate and growth rate.
    Excellent agreements are obtained between the calculated and experimental results for the effect of compositions (C, Mn, Si) on the transformation kinetics, the continuous cooling transformation diagrams and the microstructure after cooling.
  • Effects of W on Mechanical Properties and Microstructure of a Highstrength 9% Cr Heat Resisting Steel

    pp. 1034-1040

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    The change of mechanical properties and microstructure has been investigated by substituting W for a part of Mo in a 9% chromium heat-resisting steel.
    Substituting W for a part of Mo has little effect on tensile and impact properties at room temperature as well as creep rupture strength at under 600°C, but shows benefitial effects on long-term creep rupture strength at above 650°C. This is related to the fact that the substitution reduces the coarsening tendecy of precipitates and inhibits the formation of M6C which is considered detrimental to elevated temperature strength.
  • Effects of Surface Finishing Conditions and Alloying Elements on the Structure of an Iron Molybdenum Boride Base Hard Alloy

    pp. 1041-1048

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    A recently developed iron molybdenum boride base hard alloy has good mechanical properties, excellent wear and corrosion resistance. This hard alloy produced by liquid phase sintering consists of a hard phase composed mainly of a Mo2FeB2 type complex boride and an iron base, stainless steel-like binder phase.
    In the present investigation, both the effects of surface finishing condition on the binder phase and the effects of alloying elements on the structure and alloy partitioning were studied by X-ray diffractometry, Auger analysis, transmission electron microscopy, etc.
    Results indicate that the binder phase of the alloy becomes martensitic or austenitic depending on the alloy composition and sintering conditions, and that sometimes the martensitic transformation of the austenite in the binder phase is induced by surface grinding.
    This hard alloy contains the Fe2B or M6C (M : metal) phases depending on the composition in addition to the Mo2FeB2 type complex boride and an iron base binder phase.
    A martensitic binder of the alloy seems to give higher transverse rupture strength and hardness than an austenitic binder.
  • Effect of Nb and Ti on Resistance to Cold-work Embrittlement of Extra-low-carbon High Strength Cold-rolled Steel Sheet Containing Phosphorus

    pp. 1049-1056

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    The present work deals with the resistance to deep drawing-induced brittleness. The materials used in this study are 4045 kgf/mm2 grade extra-low-carbon high strength steel sheets containing P and Si as strengthening elements.
    Though the resistance to the brittleness is improved by B addition in any steel, it is more remarkable in Nb and Ti containing steel than in Nb or Ti containing one.
    The difference of the effects of B between Nb and Ti containing steel and Nb containing one is attributable to the difference of existing state of B. In Nb and Ti containing steel, B exists as solute atom because N is precipitated as TiN, thus acting to inhibit the segregation of P to grain boundaries. Solute B also en0hances the grain boundary strength by itself. On the other hand, solute B content is quite small because a considerable portion of B precipitates as BN in Nb containing steel.
    The reason why Nb and Ti containing steel is superior to Ti containing steel in resistance to the brittleness is that a small amount of solute C coexists with B only in the former. Solute C also inhibits the segregation of P to grain boundaries and enhances the grain boundary strength.
  • Application of the dj Matrix Effect Correction to X-ray Fluorescence Analysis of Electrolytic Plating Solutions

    pp. 1057-1060

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    The dj technique, the matrix-effect correction technique, which has been published as the JIS method for iron and steel analysis by XRF (JIS G-1256), was applied to analysis of electrolytic Zn-Fe alloy-plating solutions.
    The feature of this technique is that an estimated binary calibration curve is prepared for Fe i-component binary alloy system. The assumed calibration curve to analize i-component can be universally applied free from any matrix effect of sample. H2O-Metal binary solution system, however, cannot be prepared due to insolubility of metal in water.
    Then, the analytical measurements have been made on a variety of H2O-Metal-SO4 ternary system solutions to obtain an assumed calibration curve for H2O-Metal binary solution.
    dj values for each component coexisting in the electrolytic plating solution could be calculated by multiple regression analysis.
    In an attempt to analize Zn concentration in H2O-Zn-Fe-K-SO4-NH4 multi-component solutions, the present method showed good agreement with the chemical method within 0.45 g/l (σ) over the range of 430 g/l Zn.

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