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

Tetsu-to-Hagané Vol. 64 (1978), No. 3

  • 鉄鋼技術情報センターに望む

    pp. 365-366

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  • Kinetics of Reaction between Iron Oxide Slags and Solid Carbon

    pp. 367-375

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    Rates and mechanism of redcution of molten iron oxide slags with solid carbon in the temperature range from 1400°C to 1600°C have been studied. The volume of evolved CO gas as a product has been indicated on a gas flow meter, and recorded photographically. For FeO-10wt%SiO2 slag, the reduction is controlled by chemical reaction in the range where solid SiO2 does not precipitate and is controlled by FeO transport process after the range where solid SiO2 pecipitates. For FeO-CaO slag, the temperature dependency on reaction rates is negligibly small, and the product is very porous. The reaction takes place in the form of a chain of reaction consisting in reduction by CO gas and the Boudouard reaction.
  • The Kinetics of the Reduction of FeO in CaO-SiO2 Slag with Solid Carbon

    pp. 376-384

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    The rate of FeO reduction in CaO-SiO2 slag with a graphite crucible as a reductant has been determined. The testing temperature is ranged from 1400°C to 1600°C and basicity (CaO/SiO2) is ranged from 0.5 to 2.0. The reduction rate is independent on the FeO concentration in molten slag in the range of reduction degree 30% to 80%. It is found that the reduction takes place in the form of indirect reduction in which CO as reductant is consummed and regenerated by solid carbon and controlling step is the gasfication reaction. The reaction model is developed and applied to the simulation for the change of reduction degree. The CaO increases the reduction rate. This effect can be best interpreted by the foaming mechanism.
  • Melting Rates of Directly Reduced Iron Pellets into Iron Melt

    pp. 385-393

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    Effect of composition and density of pellets made of reduced iron powders as well as temperature and carbon content of iron melt on their melting rate into iron melt has been investigated. The following results are obtained:
    (1) Considering the oxygen content required to increase the melting rate, a favorable reduction degree of pellets having less than 5% gangue may be 95-98% and that of those having 5-10% gangue may be 90-95%.
    (2) In case that a slag with high melting point is formed at the melting interface of pellets, the melting rate extremely decreases.
    (3) The less the gangue content and the lower the melting point of slag made from the gangue, the greater the melting rate of pellets.
    (4) The melting rate of pellets decreases as the carbon content of iron melt decreases and is nearly proportional to the temperature of iron melt in the range from 1400 to 1600°C.
  • Rate of Desulfurization of Oxygen Containing Steel Bath and Falling Steel Droplets

    pp. 394-401

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    In order to clarify the influences of some factors on the desulfurization rates of molten steel by the slag, were performed experimental studies. The results obtained are summarized as follows:
    (1) When steels containing various oxygen contents were desulfurized the rate constants decreased with the increase of initial oxygen. At the same time, oxygen decreased with time, but the rate constants were independent of the initial content. The influence of surface active oxygen on the desulfurization rate constants was explained by the decrease in the efficient reaction area due to the absorption of oxygen at the interface and by the increase in its area due to the decrease of oxygen with the reaction time.
    (2) When the molten steel droplets fell down into the slag bath, desulfurization occurred very fast and the rate constants were 7-25 times larger than those of quiescent reaction.
  • Dephosphorization of Ferrochrome with Ca-CaF2 Flux

    pp. 402-410

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    The purpose of the present experiment was to give a new method for the production of low phosphorus ferrochrome base alloys to be added for making stainless steels with an extremely low phosphorus level. Ferrochrome base alloys containing Ni (10, 20, 25, and 30%) and C (0.03, 1, 1.5, 3, and 6%) were remelted in an ESR furnace of a small scale under an inert atmosphere. Ca-CaF2 flux was used as an electro-flux. The experimental results are summarized as follows.
    (1) Chemical analyses of remelted alloys showed that S, O, and P were simultaneously removed.
    (2) Carbon was found to be transferred from carbon-ferrochrome to the flux according to the reaction (Ca) +2C= (CaC2).
    (3) The remelting condition of alloys was determined by the melting point, Ca content of the flux, and the electric power.
    (4) The 1-3%C and 25-30%Ni alloys were smoothly remelted. The degree of phosphorus removal was high (>about 75%). The observed values of the distribution ratio of phosphorus between the molten flux and the liquid alloys were found to be close to those predicted from the relation obtained in our earlier work, Lp=4 (%Ca) (%Ca) 2.
    As for the ferrochrome and stainless steel making processes, the present dephosphorizing method can be applied to the commercial production of low phosphorus ferrochrome with about 3%C or 25-30%Ni.
  • Unusual Structure Related to the Segregation in Continuously Casting and Ingot Making Steels

    pp. 411-419

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    An unusual structure existing in the segregated position of the continuously casting plate or of the ingot steelmaking plate has been studied by metallurgical observations and EPMA analysis. The unusual structure is martensite or bainite transformed at low-temperatures. The occurrence of such transformed structure is closely related to the segregation of solute elements and mainly attributable to the segregation of manganese and phosphorus. The unusual structure consists of both martensite and bainite structure in the high strength steels of 50kg/mmmm2 tensile strength class containing high manganese contents, while only bainite structure in the steels of 40kg/mmmm2 class containing lower manganese contents. The appearance of this unusual structure has good relation to the segregated pattern obtained by micro-etching.
  • Effects of Nitrogen and Drawing Schedule on the Tensile Properties of High Carbon Steel Wire

    pp. 420-429

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    This paper describes the effects of free nitrogen (nitrogen not bound to nitride forming elements) and drawing schedule mainly on the tensile properties of patented and cold drawn high carbon steel wires. The results obtained are as follows.
    The deleterious effect of nitrogen upon the reduction of area at tensile fracture, which is apparent in the as-patented steels, gradually diminishes with the reduction by drawing and becomes negligibly small above about 60 to 70% reduction. The tensile properties of the heavily cold drawn wires are determined not by the free nitrogen level but rather by the wire drawing condition. The important role of the drawing condition on the wire strength properties is discussed in terms of the progress of the strain aging during drawing.
    The tensile-fractured steels were examined using a scanning electron microscope and it was found that in the as patented steels, the fracture pass was mainly along the proeutectoid ferrite or the pearlite boundaries and that in the heavily cold drawn ones, small voids elongated along the wire axis direction were dominant in the early stage of fracture. These fracture characteristics are discussed in relation to the tensile ductility.
    x

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  • Nucleation and Growth of Bubbles Formed by Hydrogen Attack in Carbon and Low Alloy Steels

    pp. 430-439

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    The bubbles formed by hydrogen attack in carbon and low alloy steels were observed by scanning and transmission electron microscopies. The results summarized are:
    (1) The bubbles nucleate primarily at heterogeneous nucleation sites on grain boundaries and the bubble density is essentially independent of temperature over the range of our experimental conditions. Carbides are found to be the main sites and MnS also provides the site.
    (2) The density and growth rate of bubbles depend on the heat-reatment and local microstructure and are high on the boundary of the grain containing much amount of carbide. In general, the bubble density in 2.25 Gr-1 Mo steel (except HAZ) is very low (-5×105cm-2) compared to that of other steels (-107cm-2).
    (3) Tensile stress accelerates bubble growth but does not influence the order of magnitude of the bubble density.
    (4) Coalescence of bubbles occurs, leaving low and rounded traces of the walls between bubbles.
    (5) The above observations support Shewmon's model based on Raj and Ashby's equation and his predictions for carbon steel.
    (6) The internal pressures in the bubbles were estimated by applying our data of the bubble density and size to Raj and Ashby's equation and it was found that the pressure was very sensitive to the contents of Cr and Mo in steel. This suggests that the resistivity of a given steel to hydrogen attack depends on the attainable internal pressure as well as the bubble density.
  • A Nitride Reaction of Cr2N to π Phase in High Chromium-High Nickel Austenitic Steels Containing 0.3-0.4% Nitrogen

    pp. 440-448

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    The precipitation procosses occurring during high temperature aging in high chromium-high nickel austenitic steels containing 0.3-0.4% nitrogen were followed by optical microscopy and X-ray powder difrraction analysis. Steels, mainly with a composition of 25% Cr-26% Ni-2% Mo-0.36% N, were aged at 800°C for periods of up to 10000h. X-ray powder diffraction photographs of extracted residues indicated that the precipitation of dichromium nitride, Cr2N, at the earlier stage was followed by the formation of σ phase and π phase (a nitride with the structure of β-manganese type) and that the relative amount of Cr2N in the extracted residues decreased with time of aging after 100 h. Microscopic observation of the electrolytically etched microstructure revealed that Cr2N precipitates covering entire grain boundary area at the earlier stage completely redissolved and transformed to π and σ phases after 10000h aging. The resultc onfirmed a reaction of Cr2N→π phase. It was suggested that π phase precipitation took place in steels bearing lower concentration of nitrogen without accompanying the preceding Cr2N precipitation It should be emphasized that the solubility of nitrogen in high chromium-high nickel austenltic steels was determined not by Cr2N but by π phase.
  • Effect of Impact Bending Rate on Fracture Behavior in Weldable Structural Steel

    pp. 449-458

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    Mechankal properties of weldable structural stecl (SM41) have heen studied over a wide range of nominal bending speeds ranging from 6mm/min to 40m/sec and at testing temperatures from-196 to 70°C. The results obtained are as follows,
    1) The nominal skin stress of a smooth specimen increased with lowering the test temperature and increasing bending rates. Static bending of fatigue-cracked and mechanically notched specimens did not show remarkable temperature and notch root radius dependencies except at lower temperatures, while the dynamic bending gave strong temperature, notch root radius and bending speed dependencies.
    2) The ratio of the nominal skin stress of notched specimens to that of smooth ones was increased with the decrease of notch root radius and showed no strong temperature dependency in static bending. In dynamic bending, the ratio was increased sharply with temperature and shifted to higher temperatures with bending speeds.
    3) The effect of notch root radius was not great in fracture toughness. Plane strain fracture toughness was obtained at higher temperatures in dynamic bending than in static one.
    4) The relation between cross head displacement and clip gage one was linear both for the experimental results and the finite element method.
    5) The critical COD in dynamic bending might be calculated from the relation between cross head displacement and clip gage one in static test and from the experimental equation about COD and displaccment in dynamic test.
    6) The critical COD was observed to be shifted to higher temperatures with increasing bending speeds.
  • Notched Toughness of Medium Carbon Ni-Cr-Mo Steels Having Mixed Structure of Martensite and Residual Ferrite

    pp. 459-468

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    Slow bending and Charpy impact bending tests have been performed with V-notched and fatigue-precracked specimens to study notched toughness of medium carbon Ni-Cr-Mo steels having mixed structure of martensite and residual ferrite.
    It has been found that residual ferrite, when it remained in lower tempered martensite, had detrimental effects on the slow bending and Charpy impact bending toughness even though characteristic relationship between the toughness and volume fraction of residual ferrite was found by the variation in the notched radius and loading speed. When the residual ferrite appeared in higher tempered martensite, harmless effect was found on the Charpy impact bending toughness in a state of upper shelf beyond room temperature, but the toughness became to be significantly deteriorated with a decrease in test temperature. From the analyses of microfractographs, the detrimental effect on the toughness primarily results from the fact that residual ferrite under V-notch and fatigue-precrack fractures in a brittle manner.
  • Creep Properties of 16Cr-14Ni Stainless Steel Bearing Carbon and Vanadium

    pp. 469-477

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    The creep rates were measured by the short period testing, during which the microstructural changes Were expected to be small, on 16 Cr-14 Ni stainless steels bearing carbon and vanadium with various heat treatments, and the correlation between creep rate and microstructure was discussed. For the solutiontreated condition, the creep rate of steels increases with increasing contents of both carbon and vanadium.
    The values of coefficient of stress dependence of minimum creep rate and the activation energies of the creep are 5 to 9 and 1OO to 200 kcal/mol, respectively. The increasing tendency of these values with alloying was observed. The effect of precipitated M23C6 on the creep rate was observed, that is the precipitation of a great deal of fine M23C6 carbides leads to the lower creep rate and the coalescence of the threadlike VC carbides leads to the higher creep rate.
    The creep strength of the steels with the precipitation of both threadlike VC and granular V2C carbides is smaller than that of the solution treated steels. In the comparison of steels with the similar matrix composition, however, the strengthening effect of vanadium carbide is obviously observed.
  • Effect of Alloying Elements on Creep Rupture Strength of 25Cr-20Ni Casting Steel

    pp. 478-484

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    Centrifugally casting steel HK40 (0.4C-25Cr-20Ni) is used for reformer tube in the steam reforming process or cracking tube in the equipment which produces ethylene. A study has been made of the effects of constituent elements such as C, Cr, Ni and adding elements such as Ti, Nb, Mo on the creep rupture strength of HK40.
    The results obtained are summarized as follows:
    1. C, Cr and Ni are effective to improve the creep rupture strength, where Si is sligtly effective and Mn is ineffective. With increasing Ni content, the slope of the rupture time-stress curve becomes gently and long time creep rupture strength increases.
    2. By adding Ti, Mo, V and Nb, known as carbide former, the creep rupture strength is still improved at high temperature of 982°C. Mischmetal is effective and N is ineffective.
    x

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  • Recent Development of Rolling Mill Drive Equipment

    pp. 485-490

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  • Group Method of Data Handling (GMDH) and Its Applications to the Metallurgical Processes of Iron and Steels

    pp. 491-496

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  • 報告

    pp. 497-510

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  • 抄録

    pp. 511-517

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