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

Tetsu-to-Hagané Vol. 88 (2002), No. 8

  • Structures of Molten Silicate and Aluminosilicate Slags

    pp. 419-429

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    Molten silicate and aluminosilicate slag structures have been reviewed based on the recent experimental results measured by such as Raman spectroscopy, high temperature NMR, high temperature X ray analysis. The structures of these melts discussed in this review may be summarized as follows:
    The anionic structure of alkali and alkaline earth oxide-silica binary melts can be considered a mixture of a small number of coexisting anionic units. In terms of stoichiometric expression, these units are described as SiO4-4, Si2O6-7, SiO2-3, Si2O2-5 and SiO2 units. High temperature NMR studies have made it clear that the structures of anionic units are not lasting, but exchange their structures each other very rapidly at high temperature.
    The structure of aluminosilicate melts is consistent with tetrahedrally coordinated Al3+ provided that there is a sufficient supply of metal cations for electrical charge-balance. Electrical charge-balanced alkali aluminosilicate melts consist of three-dimentionally interconnected 6-membered rings of Si and Al tetrahedral units that mix randomly. Electrical charge-balanced alkaline earth aluminosilicate melts probably consist of mixtures of three-dimentionally interconnected rings with no Al3+ (six-membered SiO2-ring), rings with Al/Si = 1(four-membered Al2Si2O2-8 rings) and rings with no Si4+ (six-membered AlO2- ring).
    In most Fe bearing silicate melts, ferrous iron is a network modifier (octahedral coordination) while ferric iron works both as a network former (tetrahedral coordination) and as a modifier depended on the slag compositions. Melts along the Na2SiO3-NaFeSi2O3 (acmite) joins become progressively more polymerized as Fe3+ content of the system increases and the end component of acmite melts has a three dimensional network structure.
  • Present Status of the Development of Smelting Reduction Technologies

    pp. 430-443

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    Summary of DIOS collaboration study with the background of the future status of Japanese steel industry is described. The feasibility study of the DIOS process indicates that it can be better applied as an alternative to the blast furnace system with capital, operational and environmental benefits. The features of smelting reduction furnace allow to be combined with other direct reduction process in the Duplex-DIOS system to expand the applicability of the technologies. The feature of the Duplex-DIOS, the combination of DIOS-SRF and Rotary Hearth Furnace, is briefly described. Several other emerging smelting technologies, HIsmelt, AusIron, ROMELT, AISI process and CCF or CleanSMelt, are briefly introduced. The comparison of DIOS technology with those processes even emphasizes the strength of the scope of the DIOS development and technology. The present status of COREX process is also described as an example of further development of the original process.
  • Relationship between Morphology of Nonmetallic Inclusion in Solidified Steel Evaluated by Fractal Dimension Analysis and Oxygen Concentration of Its Molten State

    pp. 444-449

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    Relation between morphology of nonmetallic inclusion in solidified steel and oxygen content in its molten state is examined. The oxygen content in the molten steel is observed by an oxygen sensor with solid electrolyte. It is revealed that morphology of the nonmetallic inclusion can be expressed by fractal dimension and fractal length. The larger oxygen content gives the larger fractal length. The fractal dimension of each nonmetallic inclusion is about 1.2. The fractal dimension is not affected by oxygen content in molten steel.
  • Influence of Slag Composition and Stirring Energy by Top Blowing on the Decarburization Rate of Stainless Steel in Combined Blowing Converter

    pp. 450-457

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    The decarburization mechanism of stainless steel in the low carbon region was investigated using a water model and a 178 ton combined blowing converter. The results obtained may be summarized as follows.
    1) In the water model experiments, the slag-metal interfacial area increased in proportion to the stirring energy of the top blowing gas by a factor equivalent to the 1.2 power.
    2) In comparison with conventional operation (without top blowing, CaO/SiO2=4.5) in the low carbon region, the decarburization rate increased by 1.7 times in operation with lowered slag basicity (CaO/SiO2=4.5→2.5, without top blowing ). The decarburization rate increased by 1.5 times in operation with nitrogen top blowing.
    3) A new mathematical model which considers stirring by top blowing and the slag composition was developed. In an analysis with this model, it was found that the gas-metal interfacial area increased in proportion to the stirring energy of the top blowing gas by the 0.86 power. It was possible to calculate the decarburization rate under various top blowing conditions using this relationship.
    4) The effect of lowering the slag basicity on the decarburization rate could be explained by the slag-metal interfacial area.
    5) In order to explain the effect of top blowing with nitrogen on the decarburization rate, it was necessary to consider not only the slagmetal interfacial area, but also the gas-metal interfacial area.
  • Development of a Simulator for Degradation Behavior of Emulsion-type Coolant for Cold Rolling

    pp. 458-463

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    In cold rolling, degradation of emulsion-type coolant is a crucial matter in terms of the stability of cold rolling operation or its running cost. Thus, the authors have newly developed a simulator that can investigate degradation of emulsion-type coolant. The simulator is equipped with a circulation system of the coolant, a heating system for inducing heating-degradation and a two-roller friction machine for inducing degradation due to active wear particles.
    The results showed that mean diameter fluctuation of the coolant during a degradation simulation test showed good correlation with that in an actual mill, thus indicating that the simulator can simulate the degradation of coolant in an actual mill. The results also revealed that the emulsifier type of coolant strongly affects degradation behavior.
  • Improvement of Toughness and Strength on Large Scaled SCS24 Stainless Cast Steel

    pp. 464-469

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    In order to prepare a water turbine runner for ultra high head, SCS24 was selected as a cast steel superior to SCS6, due to its more-than-ade-quate strength, and problems relating to the use of this material for large sizes were identified and the steel was modified to optimize its strength and toughness. The results were as follows.
    (1) As the target chemical composition of the cast steel was similar to that of the SUS630 forged steel that is normally used, it was found that the toughness of large SCS24 cast steel was very poor. It could be improved by adding approximately 2% Co in order to raise the Ms point.
    (2) It was found that the target values could be generally satisfied with cast steel for remelting in a 1-ton mold, and so an actual water turbine runner was manufactured. The runner had no casting defects, and structurally it was almost uniform from outside to inside. It had a uniform martensitic structure with small quantities of δ ferrite. The mechanical properties were slightly lower in the thickness transition area, but the target value for toughness was satisfied. Regarding the 107 cycle time strength in tap water at room temperature, the modified material had roughly 1.3 times higher the fatigue strength in tap water than SCS6.
    (3) Weld repairs for this material were conducted using Gas Tungsten Arc Welding (GTAW), and both the tensile properties of the deposit metals and toughness of weld joints were satisfactory. Furthermore, the microstructure of the welded boundary was uniform.
    (4) The above results confirm that the modified SCS24 is a suitable stainless cast steel for a water turbine runner that combined both high strength and high toughness.
  • Environmental Impact Analysis of ULSAB Cars and Aluminum-body Cars Using a Population Balance Model

    pp. 470-475

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    A macro model of Japanese passenger cars that a scrap ratio distribution is applied to a population balance model (PBM) is constructed. The validity of this model is shown by comparing calculation results with statistics of cars in use. Inventory factors of aluminum-body car and ULSAB (Ultra Light Steel Auto Body) car from production stage to scrapping stage are calculated, and CO2 emission amounts under an assumption that these cars popularize are analyzed. Consequently, it turns out that CO2 emission amount from ULSAB cars are less than that from aluminum-body cars. In order to make it equivalent to the total CO2 emission amount from ULSAB cars, it is shown that a recycled aluminum must be used about 50% in the aluminum-body. Moreover, in consideration of the effect on the aluminum industry by the popularization of aluminum body cars, time change of the aluminum amount which should be collected from ELV (End of Life Vehicle) is predicted, and increasing rapidly from 2010 is shown.
  • Interaction between Two Water-Air Bubbling Jets

    pp. 476-478

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