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

Tetsu-to-Hagané Vol. 50 (1964), No. 2

  • 技術革新時代におもう

    pp. 149-150

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  • Speed of Carbon Deposition in Ore Reduction

    pp. 151-159

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    PURPOSE: In ore reduction by CO at low temperature, the reaction of carbon deposition occurs violently.In a blast furnace, carbon deposit sometimes caused hanging.To clarify the kinetics of carbon deposition, this experiment was done in a stationary bed.
    METHOD: In a standard state, next factors were chosen; ore-self-fluxing sinter, size-2.5mm-5mm, weight-50g, CO flow-1Nl/min, temperature-550°C, and these factors were changed one by one. A 41mm inner diameter porcelain combustion tube was used as a reduction tube.The furnace temperature was regulated automatically.Weight of deposited carbon and reduction degree were calculated by gas volume change and CO2 concentration change through reaction bed.
    RESULTS: With a certain timelag, carbon deposit occurred at a constant speed of deposition.
    The lower the temperature the higher the speed of carbon deposition, and the lower the temperature below 450°C, the delay time of carbon deposit rapidly increases. At the higher temperature the furnace pressure rose by the smaller amount of carbon deposit.
    Carbon deposit occurred in a very thin layer.
    Ore size little influenced the carbon deposit.
    While the CO flow was not large, the speed of carbon deposition was proportional to the flow, but when the CO flow grew larger, it fell down from the proportional value.
    In reduction by N2+CO gas, the speed of carbon deposition was proportional to the CO concentration and the delay time grew long.
    In reduction by CO+CO2 gas, the speed of carbon deposition was proportional to (46-CO2%) and the delay time grew extremly long.
    When some ballast was mixed in the ore, the speed did not change. But the furnace pressure rose slightly later.The furnace diameter did not influence on the speed of carbon deposition, but the furnace pressure rose by the carbon deposit proportional to the cross secton of furnace.
    When heating at constant speed, carbon deposited under 760°C and dissolved over 760°C. Thereby the reduction degree improved very much;about 2g of carbon deposit was used by direct reduction, this was equivalent to about 25% reduction degree.(Received 13 July 1963)
  • On the Rate of Fluidized-Bed Reduction of Iron Ore.

    pp. 159-165

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    Authors presented the following empirical equation on the rate of reducing reaction. dW/d t=-K (W0-w)
    where W0 is oxygen volume combined with iron in are (g/cm3), w is oxygen volume combined with iron in are after reduction for some time (g/cm3), W is oxygen volume removed per unit time with reduction (g/min), K is reaction rate constant, and t is time (min), so that W is equal to W for t=0.
    Authors have studied on the fluidized bed reduction of iron are powder by hydrogen gasunder atmospheric or increased pressure with a laboratory scale apparatus.
    On the basis of the above equation, the mechanism of fluidized reduction was discussed.
    The results are as follows.
    1) For fluidized bed reduction under atmospheric pressure at less than 500°C, the reduction rate is considered to be controlled by its reaction rate. Meanwhile it is controlled by diffusion rate over 600°C. In the intermediate temperature region, the reduction is affected by both these rates.
    2) The reduction under increased pressure is controlled by the reaction rate near 400°C, while it is controlled by the diffusion rate over 5000°C.
    3) The effect of gas film on the surface of particles becomes important with a decreasing flow rate, especially below 20l/min for 50mm ∅; bed.
  • Influence of the Ingot Size on Segregation of S in Rimmed Steel Slab Ingots

    pp. 166-173

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    Recent advance of steelmaking, especially application of LD process has made it necessary to use an enlarged rimmed slab ingot. Under this circumstance, it became important to select the dimensions of the ingot so that the segregating zone may be as small as possible and high yield of slabbing may be ensured.
    Authors investigated the effect of dimensions of ingot on the segregation, used several experimental molds with varied thickness, height, ratio of width to thickness and weight, in Muroran Iron Works, Fuji Iron & Steel Co. Ltd.
    The obtained results were as follows.
    (1) The effect of three factors representing the design of ingot on sulphur-segregation seems to be greater in the following order;thickness, height and width.
    (2) Increase in the thickness of ingot tends to reduce the degree of max. segregation, change the location of max.segregating zone (segregating ratio is over 4).
    In the case of track-time being less than 3 hrs, two peaks of segregation appear as the thickness of ingot exceeds 800mm.
    (3) When the height of ingot is increased, the location of max. segregation is changed to top-side and the range of high segregating zone is reduced.
    (4) The high segregation of rimmed steel ingot consists of two kinds of segregation, one with the location charged to bottom-side and one with the location not changed by the dimensions of ingot.And as these segregations are overlapped, the peak appears only one, besides double peaks do as the segregation is separated.
  • Effects of Niobium on Steel

    pp. 174-182

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    As a part of the study of special chemical elements in steel, we have investigated the effects of niobium upon the properties of steel. The following are the results of test;
    1. Niobium added to steel refines remarkably the cast structure and austenite structure of steel. An adequate and yet minimum quantity of niobium necessary for the refining control of austenite--grains in steel is 0.03 to 004%.
    2. With an addition of niobium, the coarsening temperature of austenite-grains will rise. For example, in the case of 0.03 to 004% niobium addition, the coarsening temperature rises by approximately 160°C and reaches 1050°C.
    3.The deoxidation power of niobium is comparatively small and it does not show any substantial deoxidation effect upon the molten steel used for this test and other molten steels containing silicon.It is, however, considerably greater than manganese and accordingly, it is supposed that niobium may combine with oxygen which becomes super-saturated with a lowering of the temperature during the process of solidification of steel to precipitate nonmetallic inclusions consisting of various niobium oxides. But, being extremely minute and very small in quantity, such oxides do not exert a great influence on the cleanliness value of steel material as determined by JIS method. The affinity of niobium for carbon and nitrogen is so great that niobium may easily combine with these chemical elements to form carbides and nitrides.
    4. The refining phenomenon of austenite-grains is due to the existence of niobium carbides and nitrides in steel material, and the elevation of the coarsening temperature of austenite-grains is the outcome of their growth being restrained by these compounds.
    It is due to the existence of various oxides containing niobium precipitated in the molten steel or during the process of solidification that the cast structure of steel becomes refined.
    5. By an addition of niobium, the yield point and Charpy impact value of steel material are remarkably improved and the ratio of yield point to tensile strength increases.
    x

    Readers Who Read This Article Also Read

    1. Study on Low-Chromium Heat Resisting Steels for Inlet Values Tetsu-to-Hagané Vol.50(1964), No.1
    2. 特許記事 Tetsu-to-Hagané Vol.49(1963), No.11
    3. 共同研究会製銑部会報告書 Tetsu-to-Hagané Vol.49(1963), No.9
  • On the Quenching and Tempering of a Low Cr-Mo Cast Steel

    pp. 182-187

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    Changes in internal friction at room temperature of a low Cr-Mo alloy steel which has excellent resistance to tempering and low tendency to tempering brittleness were investigated together with changes in mechanical properties and micro-structures.
    Internal friction was measured in terms of free decay of transversal resonance vibration which was caused in a specimen by the electro magnetic method.
    Experimental results are as follows:
    (1) Excellent toughness and smallest value of strain amplitude independent internal friction are observed with specimen tempered at about 700°C after quenching. This is probably due to uniform distribution of fine carbides and pinning-down effects of dislocations.
    (2) A martensite structure has not strain amplitude dependent internal friction.
  • Spectrophotometric Determination of Manganese in Iron and Steel by Decomposition with Perchloric Acid.

    pp. 188-195

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    As a spectrophotometric method of manganese in iron and steel the (NH4)2S2O8 method has been mainly adopted.In this method, the sample is decomposed by a mixture of nitric acid, sulphuric acid and, phosphoric acid.
    The authors studied the (NH4) 2S2O8 method using perchloric acidic solution which decomposed the sample. It is said that conversion of Mn+2 into Mn+7 by only perchloric acidic solution is commonly unstable.
    After studying all kinds of method, authors found this method to be good as far as the amount of perchloric acid in this colored solution is 2 to 10ml.
    The features of this method are as follows:
    (1) The sample solution is easily converted into Mn+7 from Mn+2 by heating in the boiling bath for only 2 to 3 minutes.
    (2) Sufficient addition of color reagent is AgNO3 solution (0.5%) 10ml.and (NH4)2S2O8 solution (15%) 10ml.and a color develops rapidly.
    (3) Color of Mn+7 is stable for a day.
    (4) The sample containing a large amount of nickel, chromium and cobalt can easily be determined, too.
  • Beneficiation of Lateritic Iron Ores.

    pp. 196-204

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  • Methoden und Ergebnisse einer verfeinerten Konstitutionsforschung

    pp. 205-215

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  • 純酸素転炉による高炭素鋼の溶製について

    pp. 216-248

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  • 抄録

    pp. 249-251

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    x

    Readers Who Read This Article Also Read

    1. Study on Low-Chromium Heat Resisting Steels for Inlet Values Tetsu-to-Hagané Vol.50(1964), No.1
    2. 特許記事 Tetsu-to-Hagané Vol.49(1963), No.11
    3. 共同研究会製銑部会報告書 Tetsu-to-Hagané Vol.49(1963), No.9
  • 参考文献

    pp. 252-254

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  • 鉄鋼ニューズ

    pp. 258-259

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