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

Tetsu-to-Hagané Vol. 70 (1984), No. 3

  • Current and Future Problems in Coal Liquefaction Plant Materials

    pp. 299-304

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  • High Alloy Powders (I)

    pp. 305-316

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  • Reversibilities in Martensitic Transformation and Its Reverse Transformation

    pp. 317-326

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  • Accuracy of Extrapolation for Creep-rupture Strength and Standardization of Extrapolation Methods

    pp. 327-335

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  • Effects of Measuring Method on the Effective Thermal Diffusivity of Packed Coal Column during Carbonization

    pp. 336-342

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    The effective thermal diffusivity(κeff) of pulverized coal is measured by two different methods;one is "continuous heating method", and the other is "modified periodic heating method" in which the continuous heating is overlaid with periodic heating. Results with each method are similar in the temperature lower than about 750K. Above 750K, the temperature dependency on κeff is different at each method. The estimation is made on the measurement errors based on the temperature dependency of thermal properties, the heating rate and the endothermic reaction by numerical calculation. It is found that κeff is measured with high accuracy by modified periodic heating method. κeff is characterized in three temperature regions between 400 and 1 100K; in the first region, κeff is constant, in the second, κeff increases rapidly with temperature and in the third, κeff increases slowly.
  • Evaluation of Coke Strength and Reactivity Based on the Analysis of Coke Property Distribution across the Oven Width

    pp. 343-350

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    Previous researches on coke strength and reactivity have been performed without consideration of coke property distribution across the coke oven width. However, the importance and decisive effect of the coke property distribution across the coke oven width was confirmed both by experiments and by the analysis of measured results.
    The coke produced by a 250 kg electric test coke oven was devided into 10 sections across the oven width and the various coke property distributions were measured as well as coke strength and reactivity of whole samples.
    Based on the analysis of measured coke properties, it is found that coke strength can be basically evaluated by the porous material strength formula based on porosity and inherent strength. Furthermore it is found that weight loss by reaction of coke can be evaluated from porosity and the degree of graphitization, while coke strength after reaction with CO2 gas can be evaluated from porosity, inherent strength, and the degree of graphitization.
  • Investigation of Bonding Pattern of Coal Particles and Factors for Determination of Coke Properties during Carbonization

    pp. 351-357

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    The coking mechanism is considered as a process that the pulverized coal is changed into a lump of porous carbon structure after it is softened and melted with thermally decomposition by heating. From this point of view, the following items are investigated.
    (1) A bonding pattern for lumping the pulverized coal and a mechanism for the distribution of coke porosity across the oven width.
    (2) Analysis of affecting factors of an inherent strength and grafitization which are important for the evaluation of coke qualities.
  • Development of the Carbonization Simulation Model with Consideration of Coking Mechanism

    pp. 358-365

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    A simulation model which enables the estimation of the carbonizing condition in a coke oven in view of both coke qualities and heat transfer, is proposed. The validity of the model is confirmed through both laboratory-scale and actual-scale coke ovens. The features of the model are described as follows;
    (1) Density variation in the coal and coke zones across the oven width during carbonization is consecutively calculated and used as an input value for coke quality estimation and heat transfer calculation.
    (2) Porosity, micro-strength, and graphitization during carbonization are consecutively calculated and used as input values for the estimation of coke strength and reactivity. Coke strength is estimated with consideration of the effect of structual defect which may be caused by the incomplete bonding of coal particles.
  • Effects of Na2O and BaO Additions on Phosphorus Distribution between MgO-saturated CaO-FetO-SiO2-P2O5 Slags and Liquid Iron

    pp. 366-373

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    Experiments have been made to study the effect of Na2O(7-13 wt%) and BaO (4 wt%) additions on the phosphorus distribution between liquid iron and MgO-saturated CaO-FetO-SiO2-P2O5 (≤1 wt%) slags at 1550°C. The effect of Na2O or BaO on the logarithms of the equilibrium quotient, kp=(%P2O5)/ ([%P]2 ·(%FetO)5), was found to be 1.2 and 0.9 times as large as that of CaO on weight percent basis, respectively. The values for log kp can be expressed as log kp= 0.145[ (%CaO) +0.3 (%MgO)-0.5 (%P2O5)+1.2 (%Na2O)+0.9 (%BaO) ] +22810/T-20.506
    The effect of Na20 or BaO on the activity coefficients of P2O5 was also studied by the TURKDOGAN and PEARSON'S treatment. The following expression for the logγP2O5is obtained for the Na2O- or BaO-containing slags.
    logγP2O5=-1.02(23NCaO+17NMgO+8NFetO-26NP2O5+33NNa2O+42NBaO)-22990/T+9.490
  • Heat Conductivity of New Refractories for Iron and Steelmaking

    pp. 374-379

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    The heat conductivity has been measured on commercial new refractories containing large quantities of amorphous carbon and crystalline graphite. The hot wire technique was used with a thin wire of molybdenum. The thin surface layer of the sample was decarburized by oxidation in order to produce an electrically insulating layer.
    The heat conductivities have shown large temperature dependency and decreased with increase of temperature. The heat conductivity seemed very much affected by large contents of amorphous carbon and crystalline graphite.
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    2. Model Study of Gas-liquid Momentum Transfer to Design Optimum Tuyere Dimension for Bottom and Top/Bottom Blown Converters Tetsu-to-Hagané Vol.70(1984), No.3
  • Model Study of Gas-liquid Momentum Transfer to Design Optimum Tuyere Dimension for Bottom and Top/Bottom Blown Converters

    pp. 380-387

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    Cold and hot model experiments on the gas-liquid momentum transfer have been carried out to optimize the relationship among gas flow rate (Q), diameter (d), and number (N) of tuyeres through which gas is blown into the steel melt. Cylindrical and converter-type vessels were used for cold model experiments, and 5t test converter in hot metal experiments. Particular attention has been paid to investigating the leakage of liquid into submerged tuyeres, swelling of bath surface, spitting and drilling of gas jet through bath.
    Critical condition for the occurrence of leakage of liquid into the tuyere is given by constant Froude number, calculated from the critical cold and hot model data with temperature correction. The semiempirical equation for the swelling of bath surface is derived that involves energy dissipation rate and bath depth. A multiple regression analysis of the amount of spitting observed in cold model experiment has been done to find the influence of operational variables. A momentum balance between the dynamic pressure of the gas jet and the ferrostatic pressure of the bath has been examined to predict the drilling of gas jet through the bath.
    From above observation, a region on Q/N vs. d coordinates where neither leakage of liquid nor drilling of gas jet occurs has been determined and also a method has been given to optimize the relationship among Q, N, and d for satisfactory bottom blowing operation.
  • Relation between Hot Rolling Conditions and Mechanical Properties of Heavy Plates Produced from Thin Continuously-cast Slabs

    pp. 388-395

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    Continuously-cast slabs with thickness of 80, 100, 150 and 210 mm have been hot rolled to heavy plates of 31 mm in thickness after the austenitization at 1000 °C, and the effect of reduction ratio on mechanical properties of plates has been evaluated. It is demonstrated that center porosities are annihilated by hot rolling even with smaller reduction ratio than usual under the conditions that high rolling shape factor is employed for individual rolling pass. Increase in reduction ratio deteriorates the toughness of material in the short-transverse direction whereas it has no adverse effects in the longitudinal direction. Statistical analysis shows that scattering of data on absorbed energy measured by Charpy test has no positive relations with reduction ratio. As far as weldability is concerned, increase in reduction ratio markedly increases susceptibility of plates to cracking which occurs in the heat affected zone after submerged arc welding with heat input of 200 kJ/cm was applied. It is confirmed that the rolling conditions made up of high rolling shape factor and low reduction ratio, together with refinement of initial austenite grain, are appropriate for continuously cast slabs in order to improve the properties of plate which are affected by solidification structure.
  • Effect of Morphological Change of Fine Carbide Precipitates on the Ductility of Continuously Annealed Mild Steel Sheet

    pp. 396-403

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    Fundamental effects of fine carbides which precipitate during primary cooling and over-aging on the ductility of continuously annealed steel sheets have been studied based on the tensile tests, microstructural observation and quantitative analysis of carbides' size and distribution.
    The results obtained are summarized as follows:
    (1) Strength and ductility of continuously annealed steel sheets are affected by the amount of C in solution as following equations.
    Δ(Uniform-El)≅-0.09%·Δ(Q-1×104)
    Δ(Total-El)≅-0.3%·Δ(Q-1×104)
    ΔTS≅+0.06 kgf/mm2·Δ(Q-1×104) at Q-1<30×10-4
    ΔTS≅+0.18 kgf/mm2·Δ(Q-1×104) at Q-1≥30×10-4
    Q-1 : Internal friction due to C in solution.
    (2) New method for quantitative analysis of fine carbides in continuously annealed steel sheets is established.
    (3) Considering not only the contribution of fine carbides on shortening of mean free path for the precipitation of C in solution during over-aging but the improvement of post-uniform ductility due to the reduction of grain boundary carbides, the existence of moderate amount of fine carbides in ferrite matrix with the mean diameter of carbides ranging from 0.5 μm to 1.0 μm is most desirable for the mechanical properties of continuously annealed steel sheets.
  • Dimension Control of Workpieces on the Machining of Bearing Steel in Supercooled Austenite

    pp. 404-411

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    On machining of bearing steel in supercooled austenite, the dimensions of a workpiece change due to the thermal contraction and the martensitic transformation in the cooling process after cutting.
    In order to obtain the precise dimensions of the workpiece at room temperature, it is necessary to predict the dimension changes and to adjust the tool paths to compensate for them in the machining process of the steel in supercooled austenite. A method to predict the dimension change was estabished. A dimension control system for an NC machine tool was designed and its performance was proved by experiments.
    The obtained results are summarized as follows;
    (1) The thermal contraction rate of supercooled austenite of bearing steel SUJ3 is 2.2×10-5/ °C.
    (2) The final dimension (L) of a workpiece is expressed by the following equation in terms of the temperature (T°C) of the workpiece during cutting and the machined dimension (l) of supercooled austenite. L=l(1.0077-2.2×10-5×T)
    (3) In the case when the tool wear rate is small, the final dimension is controled precisely by means of the developed dimension control system which makes the compensation of the machining dimension for the dimension change predicted at each temperature of workpieces on the basis of the thermal contraction rate of supercooled austenite.
  • Grain Refinement of Ferrite-pearlite Structure of Low Carbon Steel through the Controlled Rolling Process

    pp. 412-419

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    A 0.1%C-1.35%Mn-0.03%Nb steel was hot rolled in 1 pass up to 83% reduction in thickness at a temperature between 790 and 1050 °C and deformation of austenite was examined metallographically in detail. It was found that annealing twins were formed abundantly in the austenite during heating before rolling, or during recrystallization which occurred during rolling when the rolling temperature was high. Rolling at a temperature below the recrystallization temperature of austenite resulted in severe deformation of these annealing twins. At the same time, heavy local deformation was introduced into the regions near the boundaries of these annealing twins, and also into the regions near austenite grain boundaries. Such local deformation was found to enhance the formation of ferrite nuclei in these regions during ferrite-pearlite transformation. It was suggested that this effect was most essential in the grain refinement of control-rolled steel.
  • Effects of Microstructure on Crack Growth due to Hydrogen Embrittlement in Mild Steels

    pp. 420-427

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    Since the crack growth due to hydrogen embrittlement in mild steels is accompanied with a considerable plastic deformation, the application of the linear elastic fracture mechanics to this problem is not suitable. Therefore J-integral/crack extention R-curve was applied, in order to examine the effects of microstructure on crack growth due to hydrogen embrittlement in mild steels.
    The results obtained are as follows;
    (1) With increasing hydrogen content, criticalJ-integral (Jcr) for the initiation of crack due to hydrogen embrittlement decreases slightly, but the marked decrease of the slope of R-curve was recognized.
    (2) In ferritic-pearlitic steels, the crack extended parallel to the rolling plane is much larger than that normal to it, but such a difference is quite small in tempered bainitic steels.
    (3) These results can be explained in terms of the banded structure comprising ferrite and pearlite layers. It was confirmed that both the effects of elongated MnS and texture on a crack growth are quite small.
  • Precipitation ofM23C6 and σ-phase in δ/γDuplex Stainless Steels

    pp. 428-435

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    Precipitation of M23C6 and σ-phase during isothermal aging of δ/γ duplex stainless steels has been studied mainly by means of transmission electron microscopy coupled with energy dispersive X-rayanalysis. M23C6 particles form either at γ/γ or atγ/δ boundaries. The particles are crystalographically related to either one of the γ grains atγ/γ boundaries or the γ grain atγ/δ boundaries. The M23C6 particles nucleating atγ/δ interface boundaries grow into the untransformed δ-ferrite as an M23C6/newγ eutectoid structure. The habit plane is the{111} γ//{111}M23C6, which is most parallel to the edgewise growth direction. Since C atoms formingM23C6 are supplied from theγ behind the eutectoid structure, the reaction will finally stop after entire consumption of C atoms. Thenσ-phase particles nucleate on theδ/newγ interface boundary in Nenno orientation relationship with the new γ, and grow into theδ-ferrite as aσ/δ cellular structure with the (001)σ //(111)γ habit plane. In some cases, impingements between σ andγ grains nucleating separately occur, and result in a tangled eutectoid structure without any specific orientation relationship. Since the partition of alloying elements betweenγ andδ-ferrite phases accelerates precipitation of both M23C6 and σ-phase, the solution treatment in theδ-ferrite single phase region largely retards these reactions.
  • Effect of Organic Molecules Coated on Steel Surface upon Paint Adhesion

    pp. 436-441

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    An investigation was made of the relationship between paint adhesion and the various organic compounds coated on the surface of cold rolled steel, tin-free steel (T.F.S.), and electro galvanizedsteel. The effect of the number of double bounds in aliphatic acids, functional groups in aliphatic compounds and Inductive Effect of substituted groups in aromatic molecules were discussed on the basis of the results.
    It was found that;
    (1) Unsaturated linoleic acid (double bond =2) and linolenic acid (double bond =3) improve the paint adhesion, whereas saturated stearic acid and unsaturated oleic acid (double bond = 1) arerather harmful.
    (2) Aliphatic molecules should have two functional groups to improve paint adhesion. -COOH and -NH2 are most desirable.
    (3) Effect of aromatic compounds are largely influenced by absolute values of substituent constants (Hammett's σ value). This shows that Electron Inductive Effect must be considered in the case of aromatic molecules.
  • Critical Oxygen Concentration for the Formation of CO Macroblowholes during Constant Rate Solidification of Iron

    pp. 442-444

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    The iron containing 0.050.15%C was solidified unidirectionally at a constant rate of 5 mm/min to obtain the critical oxygen concentration for CO macroblowhole formation. This concentration is represented not by a curved line but by a band. At 0.05 %C a large scatter is shown in the critical oxygen concentration. Additionally experiments were done for the ceasing of growth of CO blowholes. It is clarified that the critical oxygen concentration of blowhole formation is higher than that of blowhole growth ceasing.
  • 高炉スラグの用途別利用推移/産業災害の推移を見て

    pp. 460-460,472

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  • 抄録

    pp. 461-463

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