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

Tetsu-to-Hagané Vol. 42 (1956), No. 6

  • ON THE MAGNETIZING ROASTING OF THE Ni-Cr IRON ORE IN SOUTH ASIA DISTRICT BY FLUIDIZED BED

    pp. 461-466

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    Studies have been carried out on the method to utilize iron ore containning nickel and chromium. The authors reported already on the magnetizing roasting of Oeyama iron ore by hydrogen (Rep. Mech. Laboratory, MITI, vol. 8, 1954, 211). Recently a new type of the roasting equipment has become available. This is the fluidized-bed reactor. This roaster has many points of excellence compared with the ordinary roasting furnace. By this method, it is feasible to roast the fine ores in the stabilized condition, and this roaster is mainly applied to industry for the oxidizing roasting of sulphide ore.
    The authors trially manufactured the fluidizing roaster for magnetizing roasting of iron ores by charcoal gas. This is the report on magnetizing roasting of laterite in South Asia district by fluidized bed. These results were as follows:
    (1) Fluidizing roaster was very effective for magnetizing roasting of fine iron ore.
    (2) On the over flow products:
    Iron recovery was about 90% in A ore and 85% in B ore.
    Iron content of the magnetic concentrates was about 60% in A ore and 50% in B ore.
    Nickel recovery was almost equal to that of iron.
    Nickel content of the magnetic concentrates was 1.10% in A ore and 0.75% in B ore on the average.
    The magnetic seperation of chromium in ores was not good.
    Minimum chromium content of concentrates was 1.0% in A ore and 2.1% in B ore.
    (3) On the cyclone dusts:
    Iron recovery was about 75% in both ores.
    Iron content of the cyclone dusts was almost equal to the concentrates of over flow products.
    Nickel content was 1.0% in A ore and 0.18% in B ore on the average.
    Chromium content of concentrates was about 1.03% in A ore and 2.43% in B ore.
  • STUDY ON BLOWHOLES IN IRON AND STEEL (V)

    pp. 467-475

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    Blowholes in iron and steel are presumably due to CO, H2, N2 gases. In killed steel, so far as deoxidation is done fully, the pressure of CO gas in molten steel is very low and H2, N2 gases may become a cause of blowholes. It was explained in Report IV (Tetsu-to-Hagané, May 1956, Vol. 42, pp. 391-397) that when the H2 content was less than 8×10-4% H2, hydro- gen was not the main cause to blowhole formation if the molten steel was deoxidized fully. But in steel castings or large killed ingots, blowholes often grow in killed steel even if hydrogen content is 3-5×10-4%. Accordingly, to make clear the cause of blowhole formation in steel castings or large killed ingots, some experiments were done as follows.
    1) The same molten steel was cast in steel mold and sand molds. These patterns were all of the same size and form. Sand molds were heated at 100°C×2h, 300°C×2h, 700°C×2h before casting. These cast samples were cut and analysed with a vacuum cutting apparatus and the results obtained were as follows.
    a) It was made clear that moisture of sand molds was decomposed and became a cause of blowhole formation and in this pattern, heating temperature of sand molds at 100°C×2h was not sufficieat because of high hydrogen content in the sample.
    b) When sand molds were left long from molding to casting, the moisture absorbed by sand molds from atmosphere was decomposed in casting and became a cause of blowhole for- mation.
    2) Cylinders of 50φ×200mm were taken from the center of a 12 ton killed ingot, and analysed with a vacuum cutting apparatus, and the discharged gas was measured at room temperature. The results were as follows.
    a) Discharged gas at room temperature was mostly composed of hydrogen and the diffu- sion constant of hydrogen was of the order of 10-7.
    b) The hydrogen content in the center of large ingots was calculated from the diffusion constaat as well as the results analysed with a vacuum cutting apparatus. The results obta-ined showed 12-15×10-4% H2, and these pressure in δ-iron was higher than 1 atm. and was possible to become a cause of blowhole formation.
  • A STUDY ON THE METHOD FOR REVEALING THE AUSTENITE GRAIN SIZE IN STEEL

    pp. 476-481

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    In the present investigation, the authors developed the new method for revealing the austenite grain boundaries in the steels. The new method contained the special polishing and the proper etching of the specimens which were hardened and tempered to the brittle sorbitic structure.
    The results obtained in this investigation are summarized as follows:
    (1) When the specimens are rapidly cooled and tempered in 550°C, the austenite grain boundaries can be revealed with the etchant (Fe Cl3-HCl alcohol solution).
    (2) The grain boundaries are revealed by the dark field illumination in details rather than by bright field illumination.
    (3) The actual austenite grain sizes are more easily estimated by the new method, and the results coincide with the grain sizes obtained by the carburizing method under the same austenitizing conditions.
  • SOME ASPECTS OF GRAIN GROWTH CHARACTERISTICS OF AUSTENITE IN COARSE-GRAINED STEELS

    pp. 482-489

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    Following the previous report, (Kawai and V. Masuko, Tetsu-to-Hagane, vol. 41, 1955 p. 435) similarly from the view point of grain-growth characteristics of austenite, the author observed experimentally some practical problems concerning the grain size control in coarse-grained steels for high-pressure and high-temperature piping service.
    Results obtained are summarized as follows:
    (1) A finished product has uniform coarse grains of No. 3-No. 4 in McQuaid-Ehn Grain Size Number which are by No. 1-No. 3 less than a ladle sample. And the difference of grain
    size between a finished product and a ladle sample increases by increasing forging ratio.
    (2) The grain growth characteristics of austenite is of the so-called "gradual coarsening" type having no abrupt coarsening stage, and the coarsening temperature is lower in a fini-shed product than in a ladle sample.
    (3) In the melting of these steels, as the reducing proceeds, austenite grains become finer and the coarsening temperature rises. And by the addition of Al, austenite grains become still more finer and the coarsening temperature rises higher, but as the time passes on, the coarsening temperature falls. Moreover, the grain-refining effect of Cr additions is also observed.
    (4) Austenite grain size and the coarsening temperature have a close connection with the acid-soluble Al in steel as in the case of fine-grained steels in the previons report.
    As to Al2O3 in steel, however, the clear relation is not observed.
    (5) The reason for the difference of grain size between a finished product and a ladle sample is considered to be mainly the diminution of acid-soluble Al in steel, but, especially in the case of low-content level of it, the difference of forging ratio and the distribution state of carbides are also considerably concerned.
    (6) The relative relation of grain growth characteristics of austenite among fine-grained steel, coarse-grained steel and duplex-grained steel was clarified.
  • STUDY ON THE TOUGHNESS IMPROVEMENT BY ADDITION OF THE SMALL AMOUNT OF FERRO-TITANIUM IN STRUCTURAL STEEL (I)

    pp. 490-495

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    Titanium added in steels easily combines with sulphur and forms the stable TiS in steels. On the one hand, sulphur in alloy steels has been considered a harmful element and we have made efforts to control sulphur in steels as low as possible in steel-making process. To prevent toughness decrease caused by much sulphur in alloy steels, the auther planed to utilize small amount addition of ferro-Ti in alloy steels. Then effects of small amount addition of ferro-Ti in various kinds of structural alloy steels were examined, with both experimental small ingots and practical ingots. The following conclusions were obtained:
    1. As for the alloy element that increases toughness, titanium is more effective than molybdenum and vanadium in alloy steel.
    2. It seems especially effective to decrease brittleness in manganese-containing steel by titanium addition.
    3. Effect of a little addition of ferro-Ti in alloy steels are not so effective in steels that contains such elements, as Cr, Mo, V, etc which forms carbides easily in steels, while especially effective in steels that contains such elements, as Ni, Mn, etc which are soluble into ferrite in steels,
    4. Any steels added with small amount of ferro-Ti has very fine anstenite grains.
    5. This treatments are not effective for plain carbon steels but extremely effective for Ni-Cr-Mo structural steels.
  • STUDY ON THE HIGH SPEED TOOLS (XVII)

    pp. 495-498

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    Following the 16th report (Tetsu to Hagane Vol. 39 (1953), p. 1177), the influence of austenitizing temperatures varying from 1260° to 1350°C on the behaviour in austempering at the intermediate region (200°-400°C) and subsequent tempering was studied by micrography and hardness test with a high speed steel containing 0.65% C, 15.92% W, 4.30% Cr, 0.76% V and 2.64% Co.
    The results obtained were summarized as follows:
    In any case, at the intermediate range the isothermal transformation of austenite, such as γ→lower-bainite+γ'(austenite of higher concentration), occurred. In responset to its progress the quantity and stability of retained austenite γ' increased. Hence the more the formation of lower-bainite in austempering proceeded, the secondary hardening in subsequent tempering occurred in the larger amount and at the higher temperature. As the austenitizing temperature rose, the transformation at the intermediate range was delayed, and consequently the above-mentioned effects of austempering on the secondary hardening also became less.
  • STUDIES ON MECHANICAL PROPERTIES OF S816 AT ELEVATED TEMPERATURE (I)

    pp. 498-502

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    The authors studied the effect of solution-treatment temperature and aging on the creep rupture characteristics at 732°C and 26.6kg/mm2. The results are as follows:
    (1) Creep resistance increased by increasing solution-treatment temperature from 1150°C to 1250°C, because the carbide dissolves in matrix by high-temperature solution-treatment and fine carbides precipitated during high-temperature creep-rupture test. But creep-rupture life decreased by solution treatment at 1250°C if abnormal grain growth occurred by this treatment.
    (2) Creep ductility was not evidently affected by solution-treatment temperature, but it decreased by solution-treatment at 1250°C by the fact that the precipitation increased and that the grain size became coarser.
    (3) Creep resistance decreased by aging when the specimens were solution-treated below 1225°C, but the difference of creep resistance between the specimen aged and not aged, disappeared when they were solution treated at 1250°C. Precipitation hardening in the specimens solution treated at 1250°C was greater than the specimen solution treated at lower temperature, so the effect of aging before creep-rupture test had no effect on precipitation hardening during creep-rupture test, so creep resistance was not affected by aging. But precipitation hardening during creep rupture test decreased by aging before creep-rupture test in the specimens solution-treated at lower temperature, because preeipitation hardening was small originally at that condition, so creep-resistance decreased by aging.
    (4) Creep ductility was not evidently affected by aging, but ductility of as solution-treated specimens were inferior to the ductility of the specimens of as solution-trbated and aged, because precipitation hardening was greater in the former cases than the latter cases. These difference of ductility was more evident at the higher-temperature solution-treated specimens than the lower-temperature solution-treated specimens.
  • USE OF RARE EARTH ELMENTS IN STEEL MAKING-A REVIEW-

    pp. 503-517

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    In steel making, much attention is paid to the use of rare-earth elements on account of their very interesting and remarkable effects. Up to the present, investigations of the rareearth addition to steel has been very few and no practical application is found in Japan, while it has been already put into experimental practice in the shops under production conditions in the United States.
    In this article, the outline of the use of rare-earth elements in steel making is described based on several studies in U.S.A. and its addition is principally recommended for 3 kinds of steel as follows:
    (1) cast steel,
    (2) forged and rolled steel, and
    (3) stainless or other high alloy steel.
  • 抄録

    pp. 518-524

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