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

Tetsu-to-Hagané Vol. 66 (1980), No. 9

  • Factors Influencing Properties of Dry Quenched Coke

    pp. 1277-1286

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    In order to determine the factors responsible for the improved properties of coke quenched by the USSR type of dry quencher, study was made by conducting quenching and reheating-cooling tests on the coke produced in a 1/4 t-test oven and commercial ovens.
    The tests showed that the following three factors are influential in property improvement while heat preservation in a pre-chamber is not related with property improvement:
    1) As to chemical effect, unlike in wet quenching, water gas reaction does not occur in dry quenching, resulting in improvement of surface properties of coke.
    2) As to heat effect, dry quenching lessens residual stress in coke lumps, resulting in improvement of internal properties of the coke.
    3) As to mechanical abrasion effect, the structure of dry quencher serves to remove fragile parts from the coke.
    Internal structure models of both dry-quenched and wet-quenched coke are illustrated in the paper.
  • The Behaviour of Softening and Melting of Hematite Pellet and Sinter during Heating in a Reducing Atmosphere

    pp. 1287-1296

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    Softening and melting characteristics of some pellets and sinter during heating in a CO gas stream were examined by using an X-ray TV apparatus. The effect of load applied to the burden on its behaviour was also examined.
    The results are as follows:
    1) In the case of experiments without load, the reduction of iron oxide was nearly completed at the temperature lower than the melting point of wustite and the separation of slag from the metallic shell was not observed until the reduced iron began to melt. When some residual iron oxide existed at temperature higher than the melting point of wustite, the flowing out of molten slag was observed at relatively low temperatures, depending upon the reduction degree.
    2) Under load, the temperature at which the permeation of slag into the metallic shell and its flowing out of the pellet began was lowered and strongly depended upon the properties of the formed slags.
    3) The EPMA analysis showed that the slag formed in Hirohata pellet at 1 360°C contained a small amount of iron oxide but that in Robe River pellet at 1 168°C contained much iron oxide of about 50%. Such a high content of iron oxide lead to the formation of slag of low melting point and brought about the lowering of dripping temperature of Robe River pellet.
  • High Temperature Reduction and Softening Properties of Lime-fluxed Pellets

    pp. 1297-1306

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    This paper describes the effect of basicity, SiO2 contents and indurated temperature on high temperature properties of pellets. The high temperature properties of sampled pellets were evaluated by means of high temperature reduction test and softening test under load using 5 pellets and one pellet respectively.
    These properties depend on the forming temperature and amount of the 1st-liquid with low m.p. which is formed during the reaction between slag components and wustite. Therefore, it is effective for improving high temperature properties, that the generation of liquidus phase with higher m.p. in indurated pellets and that the increase of T. Fe-contents in pellets. In the case of lime-fluxed pellets, pellets with a mixed bonding structure, that is hematite+calcium ferrite+high basicity silica slag (and, or dicalcium silicate), show better high temperature reduction properties and softening properties.
  • Cold Model Study on the Mixing Rates of Slag and Metal Bath in Q-BOP

    pp. 1307-1316

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    Synopsis:
    Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in Q-BOP with a particular emphasis on the comparison with those of LD.
    Complete mixing time of molten steel determined by a tracer dispersion technique is, respectively, 23 to 26 sec for Q-BOP, and 100 to 200 sec for LD. This indicates that the stirring intensity in Q-BOP is remarkably larger than that of LD when compared with the same flow rate of gas. A simple relationship obtained between the mixing time, τ (sec), the flow rate of gas, Q(Nl/min) and the number of tuyeres, N is τ=41.80 (Q/N)-0.33, from which it is clear that the flow rate of gas per tuyere should be increased to realize the better mixing. Mass transfer capacity coefficient between slag and metal designated by the product of the mass transfer coefficient and the interfacial area, kBa, is given by kBa=3.49 × 10-5 Q3 for Q-BOP and by kBa=-1.53 × 10-5 Q3 for LD, respectively. Through these results, it can safely be concluded that the mass partition between slag and metal in Q-BOP is more closely linked to the thermodynamic equilibrium than that of LD.
  • Removal of Phosphorus from LD Converter Slag by Floating of Dicalcium Silicate during Solidification

    pp. 1317-1326

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    Mineralogical study of LD converter slag was carried out by means of microscopic and EPMA examinations and phosphorus was found to exist only in dicalcium silicate as solid solution. This led to the study of separation of dicalcium silicate from LD converter slag in order to remove phosphorus.
    When liquid slag was solidified slowly, most dicalcium silicate particles accumulated in the top part of the melt and fewer in the bottom. The phenomena can be interpreted as follows: on solidification, dicalcium silicate is crystallized primarily and floats up owing to the difference of density between dicalcium silicate and residual liquid. Using this phenomena enabled us to separate LD converter slag into two layers, top and bottom in a vessel. As a result of slow cooling, CaO, SiO2 and P2O5 were enriched in the top, and FeO, Fe2O3 and MnO, were in the bottom.
    Dicalcium silicate was found to be apt to separate more efficiently with higher total iron content in slag, and at higher start temperature of cooling, close to liquidus temperature.
    The efficiency of separation was improved by blowing oxygen into the molten slag before cooling.
  • Heat Transfer Coefficient in Patenting Process with Hot Water

    pp. 1327-1332

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    Heat transfer coefficients were investigated in hot water patenting process in which austenitized steel wire rods are immersed in hot water containing 0.5% polyvinyl alcohol and subjected to cooling by film boiling, and following results are obtained. (temperature in the center of steel wire rods; 900650°C, rod diameter; d=515 mmφ)
    (1) Heat transfer coefficient α is a function of rod diameter d, and following relation is obtained.α=kd-0.25 (k : constant)
    (2) α values for eutectoid steel rods having 5, 10, and 15 mm diameters are 300, 260, and 230 kcal/m2. h·deg respectively when water temperature is boiling point.
    (3) α increases greatly under sub-cool condition, i. e. by about 50% at 80°C in comparison with that at boiling temperature.
  • Effect of Rare Earth Metals Addition on the High Temperature Oxidation of 19Cr-13Ni-3Si Steels

    pp. 1333-1342

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    Effect of addition of rare earth metals (REM) up to 0.06% to Fe-19Cr-13Ni-3Si alloys containing 0.002 to 0.008% sulfur on their oxidation behavior at temperatures from 1 000 to 1 200°C in air has been investigated by thermogravimetry, metallography, X-ray diffraction, EPMA, and chemical analysis.
    (1) Good correlation between the oxidation resistance and the REM/S is found. With an increase of the REM/S, the oxidation resistance is improved under both cyclic and continuous oxidizing conditions.
    (2) In case of the low REM/S, the oxidation resistance decreases because of early formation of Fe rich oxide and Si internal oxide grows markedly into substrate.
    (3) In case of the high REM/S, REM concentrate in the inner scales and the continuous layer of Si oxide is formed beneath Cr2O3 layer, and consequently the protective scale is retained much longer.
    (4) Effect of REM on the improvement of the oxidation resistance seems that REM concentrate in Cr2O3 scales and make Cr2O3 scales more protective. REM in solution except fixed REM to sulfide are effective.
  • On the Diffusion of Ternary Electrodeposited Layers of Fe-Ni-Cr and Fe-Cr-Ni

    pp. 1343-1350

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    The study of diffusion coating on iron has been carried out.. The object of this study is how the surface laver of iron can be converted into an Fe-Ni-Cr alloy such as austenitic stainless steel.
    The diffusion process chosen for this experiment was solid state process, which was carried out by prep· aration of ternary metal layers by means of electrodeposition in an order nickel-chromium or chromiumnickel on substrate, followed by heat treatment in the temperature range from 600°C to 1000°C. In the previous paper, data on the diffusion couples consisting of Fe-Cr, Fe-Ni or Cr-Ni, were given. On the basis of these information and thickness of the interface layer in the ternary layers, the time to associate together three elements and the thickness of the diffusion layers consisting of the three elements were pre sumed.
    The time to associate was in accord with that assumed, but the thickness of the diffusion layers were greater than the expected value. The thickness and composition of the diffusion layers were determined by optical microscopy and electron probe micro analysis. One of the reasons that the latter results were shown, is considered that nickel dissolving iron or chromium has penetrated rapidly into grainboundaries.
  • Study of the Method of Controlling the Precipitation Behaviour of MnS and AlN in Unique Manufacturing Process of Grain Oriented 3% Silicon Steel

    pp. 1351-1360

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    1) The solubility product of AlN in austenite is several times as large as that in ferrite. It is, therefore, necessary to make uniform distribution of austenite phase in a steel to secure uniform distribution of precipitated AlN in the ferrite matrix.
    The microstructure of a thin plate casting of 3% silicon steel is very fine and the distribution of austenite phase is rather uniform compared with the hot rolled plate of the same steel.
    On the basis of the above findings, an unique manufacturing process of grain oriented silicon steel is proposed, which makes it possible to eliminate conventional high-temperature slab reheating. By direct casting of thin plate, the uniform distribution of AlN precipitates can be secured.
    2) The precipitation of MnS below the Curie temperature is observed to be smaller in quantity than that expected from an extrapolation of the precipitation in the higher temperature range.
    3) The unique manufacturing process proposed here can greatly save energy consumption comparing with the conventional process.
  • Effect of Austenitic Grain Size and Cold Rolling Prior to Aging on Strain Rate Sensitivity of Tensile Properties of 245 kg/mm2 Grade Maraging Steel

    pp. 1361-1366

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    An investigation has been made to clarify the effects of austenitic grain size and cold rolling prior to aging on the strain rate sensitivity in the tensile properties of a 245 kg/mm2 grade maraging steel. Austenitic grain size numbers were varied from ASTM NO. 4 to NO. 12. The temperature range in aging was from 475°C to 525°C. For the purpose of clarifying the effect of cold rolling on the strain rate sensitivity in tensile properties, fine grained (ASTM NO. 1112) plates and coarse grained (ASTM NO. 45) plates were cold rolled to 60% reduction in thickness and then aged at 475°C and 500°C. The cross head speeds in a tensile test were 1 mm/min and 0.005 mm/min.
    In aged specimens, it is found that the strain rate sensitivity in elongation is increased with increasing their austenitic grain size. This fact is considered to be due to the enhancement of stress concentrations piled up at grain boundaries in coarse grained specimens in plastic deformation.
    In cold rolled and aged specimens whose initial grain size is fine (ASTM NO. 1112), its strain rate sensitivity in elongation is higher than that of specimens with the same grain size aged without cold rolling. On the other hand, in cold rolled and aged specimens whose initial grain size is coarse (ASTM NO. 45), its strain rate sensitivity in elongation is lower than that of specimens with the same grain size aged without cold rolling.
  • The Microstructure and Toughness of Steels Corresponding to the Chemical Composition of the Segregated Zone of the Plate

    pp. 1367-1374

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    The microstructure and toughness of steels corresponding to the chemical composition of the segregated zone in the plate by continuous casting process or in the ingot by non-continuous process were investigated by means of microstructural observations and notch tensile tests to clarify the degree of embrittlement of the segregated zone.
    The nil-ductility transition temperature (NDTT) in notch tensile tests of the martensite-bainite duplex structure due to the high manganese and high phosphorus contents is above +200°C, while that of the ferrite-pearlite structure containing low manganese contents with even high phosphorus contents is below -100°C. Therefore, the embrittlement caused by the independent increase of phosphorus content is comparatively small, whereas the one caused by the formation of low-temperature transformed structure due to the increase of both manganese and phosphorus contents is large. Here the embrittlement becomes small by tempering at 650°C even when the low-temperature transformed structure is formed. The fracture mode is transferred from cleavage to intergranular with the increase of phophorus content, which bring about lower fracture strength.
  • Effect of Chromium on Creep Rupture Strength and Microstructure of 10Cr-2Mo-V-Nb Heat Resisting Steel

    pp. 1375-1384

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    The effect of chromium content on high temperature properties of ferritic heat resisting steel containing Mo, V and Nb was studied. The amount of chromium content was varied from 3% to 15% in order to obtain the optimum value. The tempering hardness and tensile strength were measured and the creep rupture tests were carried out in the temperature range from 550°C to 700°C. The microstructure was observed by transmission electron microscope.
    The results indicated that the low chromium steels had a good tempering resistance in shorter term tempering, but had a tendency to soften remarkably after longer term tempering. As increasing the chromium content up to 8%, the tensile strength increased but the ductility decreased. It was observed in transmission electron microscopy that the coalescence of precipitates was accelerated, but the recovery of matrix was markedly retarded with increase in chromium content.
    It was concluded that the optimum chromium content obtained from creep rupture tests and so on, was 10% at the temperature of 600°C.
  • A Compositional Analysis of the Solution within the Crevice on the Stainless Steels

    pp. 1385-1394

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    A compositional analysis of the solution within the crevice during the nucleation and growth of crevice corrosion in the chloride environments on the stainless steels was pertormed on the electrochemical simulation.
    The experimental results are following:
    (1) Charge passed during electrolysis was in the linear relationship with the concentration of metallic ions in the crevice. No selective dissolution for the alloying elements was observed during electrolysis.
    (2) Chloride ion concentration in the crevice solution has a linear relationship with the metallic ion concentration dissolved into the crevice. Ratio of chloride ion concentration to metallic ion concentration depends on the chloride ion concentration in the environment out of the crevice.
    (3) pH of the crevice solution was dependent on the ratio of chloride ion concentration to metallic ion concentration of the crevice solution and charge passed into the crevice during electrolysis.
  • Application of High-frequency Inductively Coupled Plasma Emission Spectrometry to Analysis of Iron Ores

    pp. 1395-1400

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    Synopsis:
    An application of Inductively Coupled Plasma-Optical Emission Spectrometry to iron are analysis was studied. Sample was easily fused with mixed flux (Na2CO3+Na2B4O7 :1 + 1). Fused sample was dissolved with HNO3 to prevent silica gelation. It was able to determine simultaneously SiO2, Al2O3, CaO, MgO, TiO2, Mn, P, Cu, Zn, V, and As, by this method, which needed two minutes for analysis of one sample solution. However, in the case of trace analysis, high relative ratio of background to the signal of analytical element caused decrease of analytical precision, and the analytical results of some elements were necessary to be corrected by Fe amount.
    Good precision was obtained by this method compared with conventional method of chemical analysis.
  • Influences of Non-metallic Inclusions on Emission Spectrometric Analysis of Steels

    pp. 1401-1405

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    On emission spectrometric analysis of steels, the behavior of non-metallic inclusions was investigated. The spectrum intensity of determinable elements was influenced in complicated manners by inclusions. Experiments were carried out concerning the considerable influence of Al2O3 inclusions on C and additionally those of SiO2 on C and Al2O3 on P as similar pattern.
    Obtained results were following:
    1) The influence of Al on C was caused not by contents of Al on composition of inclusions themselves, but by existing condition of Al2O3 inclusions.
    2) The influence of inclusions was attributable to the abnormal emission caused by preferential discharges, and similar behavior was also shown on SiO2 inclusions to C and Al2O3 inclusions to P.
    3) Because of influence of inclusions mentioned above, calibration curves could not be unified and the influences might not be reduced without the classification of calibration curves.
  • Thermodynamics of liquid Fe-C-O System

    pp. 1406-1422

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  • Surface Hardening of Steel by Nitriding Method

    pp. 1423-1434

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  • 誌上討論

    pp. 1435-1436

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  • 良い英文を書くために

    pp. 1437-1440

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  • 抄録

    pp. 1444-1450

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