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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 34 (1994), No. 12

  • Transformation Textures in Steels

    pp. 927-942

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    DOI:10.2355/isijinternational.34.927

    During the hot rolling of steels, the parent austenite phase develops a crystallographic texture. As a result, the material after transformation (ferrite, martensite, acicular ferrite, or bainite ) also acquires a texture which is related in a precise way to the texture of the parent material. The major component of the transformation texture derived from recrystallized austenite is the {001} <110>, which originates from the cube {100} <001> component of the parent texture. The major components of the texture of pancaked austenite are the Bs {110} <112> and Cu {112} <111>, and these give rise, respectively, to the {332} <113> and {113} <110> components in the transformation product. The Goss {110} <001>, Goss/Bs {011} <511>, Bs/S {168} <211>, S{123} <634>, and S/Cu {236} <322> orientations in the deformed austenite also contribute to the formation of the overall transformation texture. Since more than one parent γ orientation can transform into the same bcc orientation, it is sometimes impossible to determine, unambiguously, the origin of particular transformation texture components in the parent γ texture.
    The intensity of the overall transformation texture can be increased by the addition of Nb, Ti and V to steel, by giving large reductions during controlled rolling, and by using lower finishing temperatures during processing. Among the transformation texture components, the {332} <113> is the most beneficial from the point of view of achieving good deep drawability and improved strength and toughness. The presence of substitutional solutes such as Mn, Ni, Cr or Mo, finer austenite grain sizes and faster cooling rates during transformation increase the intensity of the {332} <113> component. By contrast, the intensity of the {113} <110> component remains relatively insensitive to the above factors.
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  • Interfacial Phenomena and Computational Fluid Mechanics in Materials Processing

    pp. 943-950

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    DOI:10.2355/isijinternational.34.943

    A general formulation is presented, describing the behavior of three systems of importance in metals processing, where interfacial phenomena play a key role in affecting the overall flow behavior. These three systems include gas plumes in liquids, electomagnetic stirring of continuous casting systems and spray forming. In the model, allowance is made for the forces in the liquid that are due to fluid motion and the effect of interfacial tension. The results include the representation of the plume shape in the multi-phase system, the free surface behavior in continuous casting and the evolution of a droplet shape in spray forming.
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  • Surface and Interfacial Tensions of Iron Based Systems

    pp. 951-959

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    DOI:10.2355/isijinternational.34.951

    A description is given where surfaces are treated as separate phases with a thickness corresponding to a monolayer. The surface tension of liquids is a measure of the excess chemical potential of the surface atoms relative to the bulk atoms. Equations for the calculation of the surface composition and surface/interfacial tensions of liquid mixtures are developed.
    Excellent correspondence between calculated and experimental surface/interfacial tension values was obtained for several non-ideal iron based systems, including Fe-Si, Fe-Cu, Fe-O and Fe-slag systems. When a low surface tension solute (Si) is added to a solvent with a high surface tension (Fe), the solute generally tends to concentrate on the surface and the surface tension of the mixture is decreased. However, in cases with strong chemical interaction such as between Fe and Si, Si is drawn into the bulk of the Fe. This results in surface tension values with positive deviation from the additive rule.
    In terms of iron-slag interfacial tensions, the presence of slag components which increases the activity of oxygen due to iron-slag exchange reactions, will reduce the interfacial tension. These slag or slightly higher than that of FeO.
  • Swelling of Iron Ore Pellets under Non-isothermal Condition

    pp. 960-963

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    DOI:10.2355/isijinternational.34.960

    In the present investigation an attempt has been made to study the swelling behaviour of iron ore pellets. The test were conducted under non-isothermal condition in the temperature range 800-1000°C. The variable parameters studied are partial pressure of carbon monoxide gas, flow rate and heating rate. The experiments were statistically designed so that the effect of each variable and interactional effect of different variables can quantitatively be assessed. Attempt has also been made to know the effect of gangue content and porosity of the pellet. The results show increased swelling index with increase in heating rate, partial pressure, flow-rate and porosity and with decrease in gangue content. The regression equation obtained after statistical analysis is given by
    Y=52.875+8.625X1+7.625X2+2.375X3
    Where, X1, X2 and X3 represent the heating rate partial pressure and flow rate in coded form: Y=Swelling index of the pellet.
  • Influence of Al2O3 on Reduction-Meltdown Behavior of Sinter in Blast Furnace

    pp. 964-972

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    DOI:10.2355/isijinternational.34.964

    At Kimitsu No. 3 sintering machine, a test was performed which produces a low-Al2O3 content (1.50%) sinter in contrast to an ordinary sinter (Al2O3=1.85%). Together with tests performed to check the availability of this sinter at Kimitsu No. 3 and No. 4 blast furnaces, off-line model experiments were conducted with the use of the same sinter. The results obtained are as follows:
    (1) Keeping the sinter cold strength raised by lowering Al2O3 content at a fixed level has enabled a sintering with low energy (lower FeO content) to be done and the reducibility has been improved from ordinary 60% to 68% in JIS-RI.
    (2) Through the off-line model experiments using this sinter and the tests with the use of the same sinter at the actual furnaces, the raise of a shaft efficiency of 2.0 to 2.5% has been attained with the raise of JIS-RI of 5% at the lumpy zone of blast furnace.
    (3) At the cohesive zone accompanied with the formation of melt exceeding 1150°C, the amount of FeO-containing melt formed has decreased and the chance of pores being stopped up by the melt has diminished thanks to the improved reduction efficiency and the decreased Al2O3 and SiO2 contents, which has led to a better permeability at the cohesive zone. Then, the resultant merit has brought the improvement in permeability of the blast furnace, which is verified by the foregoing off-line model experiments and actual furnace tests.
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  • Fluid Flow Phenomena in a Cylindrical Bath Agitated by Top Lance Gas Injection

    pp. 973-979

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    DOI:10.2355/isijinternational.34.973

    Fluid flow phenomena in a cylindrical bath agitated by gas injection from a submerged top lance were investigated on the basis of cold model experiments. A swirl motion of liquid, which was sumilar to the rotary sloshing, was observed under a certain blowing condition. The critical condition for the cessation of the swirl motion was first experimentally clarified and subsequently the following experiments were made in the absence of the swirl motion.
    The vertical migration distance of bubbles from the lance exit was measured using an electro-resistivity probe, and an empirical correlation for it was proposed as a function of the modified Froude number. The axial and radial velocity components of liquid were measured for a water-air system using a two-dimensional laser Doppler velocimeter. Applicability of previous emperical correlations of the axial mean velocity proposed for the gas injection through a centric bottom bozzle to the present case was examined. An electro-chemical method was used to measure the mass transfer coefficient between a platinum flat plate and aqueous FeSO4 solution. In the region below the bubble plume, the so-called dead water region was observed.
  • Continuous Measurements of Bubble Characteristics in a Molten Iron Bath with Ar Gas Injection

    pp. 980-985

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    DOI:10.2355/isijinternational.34.980

    Present authors developed a new electro-resistivity probe being able to continuously measure bubble characteristics in a molten iron bath agitated by gas injection. The life of the probe was about two hours at a bath temperature of 1250°C. The axial and radial distributions of gas holdup α, bubble frequency fB, mean bubble rising velocity uB and mean bubble diameter dB were determined for the Ar gas flow rates of 50 and 100 cm3/s (at 1250°C). The Ar gas was preheated up to 1250°C and then injected through a single-hole centric bottom nozzle.
    The results were compared with empirical correlations derived from cold and hot model experiments. The measured values of α, fB and uB in the upper part of the bath were approximated satisfactorily by correlations proposed by the present authors, but they did not agree with the experimental results of Kawakami et al. The measured values of dB were a little smaller than predicted values by Sano et al. and Irons et al.
  • Relationship between Primary- and Secondary-dendrite Arm Spacing of C-Mn Steel Uni-directionally Solidified in Steady State

    pp. 986-991

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    DOI:10.2355/isijinternational.34.986

    The relationship between primary dendrite arm spacing and secondary one was investigated in experiment, and was found that the latter is roughly one half of the former. Theoretically, the primary arm spacing is interpreted by thermodynamic perturbations ahead of the primary tip. On the contrary growth mechanism of secondary arm is ascribed to Ostwald-ripening and/or sintering/coalescence mechanism. The experimental result is analysed by the mechanisms, and is shown the 'one half relationship' is a good approximation.
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  • Consideration on Distribution and Size of Dendritic Type II MnS-inclusion in Steel Dendrite Structure

    pp. 992-996

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    DOI:10.2355/isijinternational.34.992

    Rod diameter of Type II manganese-sulfide inclusion precipitating in residual melt among steel dendrites is observed. The data about relationship between diameter, distribution/size of the inclusions and steel dendrite arm spacings were considered. The sample steels solidified under several steady state uni-directional solidification conditions. The consideration was done from a view point of cooling rate dependency of MnS-dendrite arm spacings, taking cooling behavior as well as shrinkage of the residual melt pool into account. The result in experiments that rod size of MnS-inclusions is correlated to Solidification-Unit-Cell volume is explained from cooling behavior of the residual melt pool.
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  • Characteristics of Flow Injection Inductively Coupled Plasma Mass Spectrometry for Boron Analysis in Steels

    pp. 997-1001

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    DOI:10.2355/isijinternational.34.997

    A method for the determination of Boron in steels by FI-ICP-MS is described. It is shown that flow injection (FI) can alleviate problems arising from high amounts of dissolved solids in Inductively Coupled Plasma Mass Spectrometry (ICP-MS) due to the capability to operate with microliter amounts of sample with a rapid sample rate. Sample dissolution was carried out in a microwave oven using diluted aqua regia (HCl+HNO3, 3+1) and high pressure digestion vessels, which gave notable advantages over conventional dissolution techniques, such as lower costs, greater volatile retention, reduced contamination and faster dissolution rates. The operating parameters in flow injection ICP-MS, such as carrier flow rate, nebulizer flow rate, and injection volume were established. The detection limit obtained when direct sample nebulization was used, with a 0.05% m/v Fe concentration, was 1.2 μg·g-1 B, compared to a detection limit of 0.2 μg·g-1 when the FI system was used with samples containing a higher concentration of dissolved solids (0.5% m/v Fe). The influence of the internal standard on precision and accuracy was studied and Beryllium was selected as the internal standard. The RSDs obtained for four peak area determinations of 200 μl injection volumes of a solution of 100 ng·ml-1 B in the presence of 0.5% m/v Fe were below 1.5%. The accuracy of the method proposed was verified by analyzing Reference Materials (EURONORM-CRM 097-1; BCS 456, 457 and 460; NBS 361, 363 and 365), using an external calibration system with calibration samples, prepared from a standard Boron solution, in the same acid medium as the test sample solutions.
  • Effects of Electrolyte on the Morphology of η–Zinc Crystals Electrodeposited on Steel Substrate

    pp. 1002-1007

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    DOI:10.2355/isijinternational.34.1002

    The effects of electrolyte composition, i.e., sulfate or chloride bath, on the morphologies and the crystallographic properties of the η-zinc crystals deposited on a steel substrate have been investigated by means of back reflection X-ray Laue technique and scanning electron microscopy. The results obtained are as follows:
    (1) η-zinc crystals electrodeposited epitaxially on the ferrite substrate surfaces were related to the ferrite with the Burgers orientation relationship in the both cases, the (0001) basal plane of zinc crystals lying close to the {110} ferrite plane most parallel to the specimen surface.
    (2) The morphology of the epitaxially grown η-zinc crystals depends on the composition of the bath. In the case of the sulfate bath, η-zinc crystals consisted of a variant of the thin layered hexagonal crystals. Whereas in the case of chloride bath, thin hexagonal plates stacking one over one in one or two directions as if they fell like dominoes were observed.
    (3) Such morphological differences can be explained in terms of the nucleation sites which were formed on the substrate surfaces by the immersion in the electrolytes.
  • Effects of Rolling Reduction and Annealing Temperature on the Recrystallization Structure of Solidified Columnar Crystals in a 19% Cr Ferritic Stainless Steel

    pp. 1008-1017

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    DOI:10.2355/isijinternational.34.1008

    The cold-roling and recrystallization behavior of solidified columnar crystals in a 19% Cr ferritic stainless steel has been investigated. As the rolling reduction increased, the recrystallization rate increased and the recrystallized grain size decreased. However, the (001) [110] initially-oriented columnar grains were hard to recrystallize without regard to rolling reduction so that the recrystallization structure was very inhomogeneous in grain size even in a heavily-rolled (90% rolled) specimen. The recrystallization rete of 70% rolled specimens increased as the annealing temperature increased. In particular, at the temperatures where carbides did not precipitate the recrystallization rapidly completed and a coarse-grained structure formed in a short time annealing because of rapid grain growth. As a result, in the Fe-19% Cr ferritic columnar crystals a favorable recrystallization structure with fine and uniform grain size cannot be obtained simply by increasing rolling reduction or by controlling annealing temperature.

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