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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 89 (2003), No. 2

  • Improvement of Mathematical Model of Blast Furnace and Its Application in Practical Operation

    pp. 211-220

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    Mathematical model of blast furnace operation has been being developed for about four decades. One of the major model frameworks consists of balance of mass, momentum, thermal energy and materials, transport phenomena theory, and chemical kinetics. The models on this basis have been extended from one-dimensional to multi-dimensional, and from steady to transient. This progress has improved the model accuracy and applicability. Although this model extension raised the computational load, recent progress of computer science and technology allows us to get the computed results in practical time period, and shows the capability to apply numerical simulation in the practical operation of blast furnace.
    This paper gives an outline of the recent mathematical model of the blast furnace operation, and some applications to the novel operation such as scrap charging and top gas recycling. Next, the expected phases of the model application in the practical operations are shown. Finally some phenomena to be clarified and formulated that are indispensable for the further development of the blast furnace models, and a new direction of model development, such as stochastic process and discontinuity, are shown.
  • Recent Progress in Analytical Models for the Simultaneous Optimization of Deformed Geometry and Microstructure

    pp. 221-228

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    Geometry of formed product and mechanical properties are the most important functions which are required in the products in metal forming processes. Numerical analysis for the evolution of microstructure in cold forming and hot forming is the key tool usable for the simultaneous optimization of geometry and mechanical properties of formed product. It is helpful not only to reduce time and cost for optimization but also to renovate design sequence of steel product.
    Novel design of steel product will be the combined design of forming condition and alloy composition, which is operated fully on digital computers. Here, components are 1) macro-process simulation, 2) micro-process simulation, 3) mechanical properties simulation as a function of microstructure and 4) material genom, and 5) nano-process simulation should located behind material genom and mechanical properties simulation as a function of microstructure. Analytical methods for the analyses of microstructure evolution for the forming of steels are reviewed in this paper. Their present standpoint and recent achievement will be explained, and its expected advance in future will be discussed.
  • Indirect and Direct Reaction Rates and Acceleration Effect in Wustite-Coal Char Composite Pellet Heated at Elevated Temperature

    pp. 229-236

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    The weight loss curves of wustite-coal char composite pellet were measured and the rate is proved to be much faster than the overall rate of the indirect reactions of reduction and gasification. The indirect reaction rates were calculated by substituting the rate constant of reduction and the constant of iron catalyzing gasification estimated by the reduction of the wustite and the gasification of the char in electrolytic ironchar composite pellet into the rate equation of the grain model. The large difference in the experimental and calculated weight loss curves may be attributed to the direct reactions of wustite with char and carbon dissolved in reduced iron. The weight loss curves of the direct reaction were gravimetrically measured in vacuum. The experimental weight loss curves were still significantly faster than the sum of the weight loss curves of the calculated indirect reactions and the direct reactions in the later stage of the reactions of the composite pellet. It was reasonably concluded that the significant acceleration effect of the close mixing of wustite and char in the pellet can be attributed to the direct reduction of wustite with dissolved carbon in indirectly reduced iron.
  • Relationship between the Assimilation Properties of Fine Ores and the Strength of Sinter

    pp. 237-243

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    Ore properties influence the strength of sinter. It should be evaluated separately for coarse particles and for fine particles because of the different behavior during sintering; that is, the former remains as unmelted parts in sinter and the latter melts to be bonding phase. This report focused on the assimilation behavior of fine particles and showed a relationship between the behavior and the strength of sinter.
    Press-formed tablets consisting of fine ores (-0.5 mm) and limestone (-0.5 mm) (fine ore/limestone=10/1) were heated at 1300°C in an electric furnace with air flow. The heated specimens were observed with microscope and the pore structures were analyzed with image processing.
    The crushing strength of tablets after the assimilation test decreased with an increase in porosity. The porosity was influenced by the number of pores more than the diameter of those. The number increased with an increase in Al2O3 content of the ore. Sinters after heating quasiparticles with varying adhering fines showed similar behavior concerning the pore formation and its influence on strength. In conclusion, Al2O3 content of adhering fine was favorable to be less than 1.5 mass% and nuclei are was desirable to contain less combined water.
  • Characteristics of Gas Flow in Laval Nozzle with Sub-hole for RH Multi-function Treatment

    pp. 244-251

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    The purpose of the present paper is to decide the form and dimensions of the practical fuel injection nozzle used to RH-treatment. The distribution of static pressure in the nozzle and the velocity at the outlet of the nozzle are investigated. From the results for four types of nozzles and theoretically calculated pressure distributions, the flow behaviors of gas in the nozzles with and without a sub-hole are discussed as the case of reheating the refractory surface under atmospheric pressure and the case of keeping the temperature of molten steel under almost vacuum state.
  • RH Treatment by Laval Nozzle Lance with Sub-hole

    pp. 252-257

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    The purposes of combustion by multi function burner lance are skull-less operation of vacuum vessel, increasing the temperature of molten steel, and improving the decarburizing rate. In this paper the decarburizing rate is investigated in case of oxygen blowing and burning with excess oxygen.
    Oxygen blowing can improve the decarburizing rate with the RH multi function burner lance even if carbon content in molten steel is high before RH-treatment.
    Neither pollution nor the decrease in the quality was seen from the composition change of molten steel in RH treatment and the quality investigation of the product in operation with RH multi function burner lance.
  • Desulfurization with RH Multi Function Burner Lance

    pp. 258-264

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    It was expected that the desulfurization is improved by flux injection into the burner flame of RH multi function burner lance, because of melting of flux by burner. The desulfurization of 100 ton RH was experimented by RH multi function burner lance with flux.
    Sulfurization constant Ksis related to top slag (T.Fe+MnO) as follows
    Ks =0.04 × {(T.Fe+MnO)-2} (T.Fe+MnO) ≥2
    Ks=0 0≤(T.Fe+MnO) ≤2
    Desulfurization constant Kds with flux by burner carrier is larger than that by argon gas carrier.
    In case of burner condition, the concentration of sulfur of flux in molten steel is high and it is supposed the evidence of flux melted.
  • Numerical Prediction of Solidification Structure Taking Account of Molten Steel Flow

    pp. 265-272

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    The casting experiment by using vertical type continuous casting machine was performed in order to clarify the effect of electromagnetic stirrer (EMS) on the solidification structure. It has been confirmed that the ratio of equiaxed zone increases and the size of equiaxed crystal and segregated area in the center of billet becomes finer with the application of EMS. The numerical model of columnar to equiaxed transition (CET) was constructed with consideration of molten steel flow to examine the mechanism of the changes in the solidification structure. It has been estimated by the model that the enlargement of undercooled region and the increase of grain density of equiaxed crystal lead to the refinement in solidification structure with the application of EMS. Moreover, the effect of superheat and casting speed on the ratio of equiaxed zone has been analyzed by using the present model and the obtained results show good agreement with experimental ones.
  • Effect of Strain on Microstructures and Mechanical Properties of ARB Processed and Annealed Ultra-low Carbon IF Steel

    pp. 273-280

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    Ultra-low carbon IF steel was deformed to various strains ranging from 0.8 to 5.6 by the accumulative roll-bonding (ARB) process at 500°C, and subsequently annealed at various temperatures for 1.8 ks in order to clarify the effect of strain on the microstructures and mechanical properties. The materials deformed by relatively low strains below 2.4 revealed dislocation cell or subgrain structures including small number of deformation induced high-angle grain boundaries. The microstructural change in these materials during annealing was understood in terms of discontinuous recrystallization characterized by nucleation and growth. The materials severely strained over 4.0, on the other hand, were filled with the pancake-shaped ultra-fine grains surrounded by high-angle grain boundaries. The mean thickness and length of the pancake-shaped ultra-fine grains were about 200 nm and 900 nm, respectively. The specimens ARB processed above strain of 4.0 performed very high strength up to 900 MPa, though they showed limited elongation. Normal grain growth with recovery at grain interior occurred during annealing of the highly strained materials, because all the boundaries surrounding the ultra-fine grains had equivalent degree of mobility. The 0.2% proof stress of the specimens having various grain sizes held Hall-petch relationship. It was also clarified that high-angle boundaries could contribute more greatly to the strength than low-angle boundaries. In contrast, the uniform elongation of the ultra-fine grained materials whose mean grain sizes were smaller than 1 μm suddenly decreased to about a few percents because of the early plastic instability. It was concluded from the present study that strain over 4.0 is necessary to obtain uniform ultra-fine grains having high strength.
  • Characteristics of Steel Plates Rolled with Shear Deformation

    pp. 281-288

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    The mechanical properties of the plates rolled with shear deformation are compared with those of conventionally rolled plates. The pair cross rolling is employed to introduce uniform shear strain through the plate thickness. The introduced shear strain and the equivalent strain are evaluated from both experimental and numerical analyses. A 12 mm thick plate with a fine ferrite grain under 2 μm is produced using the pair cross rolling mill, and tensile and the sharpy impact tests are carried out. The interesting effect of the shear deformation is discussed from the viewpoint of the tensile strength and the energy transition temperature. The result shows that the addition of shear deformation can become an effective method for improving the strength and the energy transition temperature of steel plates.
  • A New Etching Method of Deformation-induced Martensite in Type 304 Stainless Steel Hot Rolled Plate

    pp. 289-296

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    A two-step etching method was devised so as to visualize the deformation-induced martensitic phase, α', in an austenitic stainless steel SUS304. The method, a combination of an electrolytic and a chemical etching, selectively etched α' phase. The visualization of martensitic phase utilizes the etch-pit row formed by the present etching method. In a 3 mm-thick plate subjected to a three-point plane-strain bending using a punch of 6 mm in radius, the amount of surface-strain was almost constant in an angle range of ±35° from the bending center, but decreased in higher angles where the amount of the surface-strain remained higher than that on the outer surface. The amount of α' was higher on the inner surface than that on the outer surface even at the same level of strain. The amount of spring-back was 10° in 180° bending, presumably due to the different distributions of α' phase.
  • Ferrite Grain Refinement of Ti-added Low Carbon Steel through Dynamic Recrystallization in Austenite Region

    pp. 297-302

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    Effect of grain size and deformation condition on dynamic recrystallization behavior of Ti-added low carbon steel in austenite region was studied mainly through hot-compression test. When initial austenite grain size was smaller than 50μm, a peak of true stress, which is characteristic of dynamic recrystallization, was observed even in high Z (Zener-Hollomon parameter) region such as at 1123K and at the strain rate of 0.4/s. The small austenite grain can be obtained when more than 0.15% Ti is added and the steel is reheated at the temperature of lower than 1423K. In this case, it is considered that TiC precipitates should prohibit the grain growth of austenite during heating. The peak stresses in various deformation conditions were expressed by Z parameter, from which the apparent activation energy was calculated as 340 kJ/mol. The typical final grain size of ferrite after dynamic recrystallization and transformation at the cooling rate of 50K/s was 25μm. It is estimated that the effect of solute C and solute Ti on dynamic recrystallization was very limited.
  • Chemical Composition Dependence of Magnetostrictive Properties of Fe-Pd Alloy Films

    pp. 303-308

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    The Fe-43.8at%Pd, -60.3at%Pd and -66.9at%Pd alloy films were prepared by DC magnetron sputtering method. The structures of Fe-Pd alloy films were mainly fcc phase and partially fct phase. The compressive residual stresses were generated in films on film formation. In addition, the good correlation was obtained between compressive residual stress and coercive force of Fe-Pd alloy films. The Fe-60.3at%Pd alloy film has the largest compressive residual stress, the largest coercive force and largest magnetostriction. The magnetostrictive susceptibility largely depends on the magnetic susceptibility. These changes in the properties depend on the composition rate of Fe-Pd alloys.
  • Analysis of No.3 Blast Furnace Operation of TangGang Works at China Based on Rist Diagram

    pp. 309-314

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    By applying the Rist model to the blast furnace No.3 of TangGang works (China), the operating lines were calculated through which the coke rate and fuel rate were evaluated. The obtained data were compared to the operating lines in the blast furnace of Muroran works of Hokkai steel. The estimated comparative data clarified the effects of the various operating parameters on the operating line of the blast furnace No.3 of TangGang. From these parameter dependencies, the cause of the high coke rate of the blast furnace No.3 of TangGang works have been discussed; a strong measure for the reduction of the coke rate have been suggested. According to the above, it was confirmed that the Rist model was very effective method to solve the real problems of blast furnaces despite of its simplicity.
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  • Determination of Copper in Steels by Inductively Coupled Plasma Atomic Emission Spectrometry with Gas-phase Sample Introduction Technique

    pp. 315-320

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    Copper in steels was determined by inductively coupled plasma atomic emission spectrometry with gas-phase sample introduction in a reaction medium of citric acid. The gaseous copper species, as yet unidentified, was phase-separated in a gas-liquid separator and directed via a stream of argon carrier gas to an inductively coupled plasma for atomic emission spectrometry. Under the optimized experimental conditions, the best attainable detection limit at Cu I 324.754 nm line was 1.5 ng/ml with a linear dynamic range of 10 to 500 ng/ml in concentrations. The presence of several diverse elements was found to cause more or less a depressing interference by the proposed technique. When copper in steels was determined, a large amount of iron in the solution caused a severe depressing interference. Of the extraction solvents examined, diethyl ether was found to be the most preferable to separate iron from copper in the sample solution. The proposed method was applied to the determination of low concentrations of copper in steels. The results obtained by this method were in good agreement with the certified values.

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