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

ISIJ International Vol. 31 (1991), No. 7

  • Strip Casting Techniques for Steel

    pp. 661-668

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    DOI:10.2355/isijinternational.31.661

    The concept of casting molten steel directly into strip can be traced to the work of Sir Henry Bessemer. A version of Bessemer's concept can be seen in state-of-the-art continuous casting techniques for large section slabs, and an extension of CC slab casting known as thin slab casting is also nearing commercial use. On the other hand, the development of a practical strip caster with thickness ranging from several hundred microns to about 10 mm is still in the research stage. This paper describes the main trends in the development of strip casting techniques in terms of both processes and material characteristics. The twin-roll caster is the main trend in Japan, while the single-roll caster forms the mainstream in the United States. The answers to a questionnaire indicated that surface quality is the most serious impediment to the realization of a practical process, followed by strip shape. To date, the merits of process integration have usually been discussed in terms of the relative energy requirements of the respective processes, i.e. in terms of energy saving. However, the additional energy reductions which can be achieved by the strip caster in place of the conventional slab CC are marginal. Instead, reductions in finishing cost are considered to be an appropriate indicator of economic benefit where the strip CC is concerned. Thus, the goal of the race in developing a commercial strip caster is to establish techniques to assure good surface quality.
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    1. Effect of Technological Factors on Strip Profile in Twin-roll Casting Process ISIJ International Vol.38(1998), No.10
    2. Strip Quality of Highly Alloyed Metals by Twin Roll Casting ISIJ International Vol.31(1991), No.7
    3. Relationship between Flow Characteristics and Surface Quality in Inclined Twin Roll Strip Casting ISIJ International Vol.36(1996), No.6
  • Improvement in Performance of the Blast Furnace at Bhilai through Statistical Analysis and lmprovement in Burden Preparation

    pp. 669-676

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    DOI:10.2355/isijinternational.31.669

    The present paper reports the performance analysis of the blast furnace 'X' of Bhilai Steel Plant (BSP). Special reference has been made to the process variables related to the burden, such as sinter. The analysis shows that the burden rate has been the most significant variable for the coke rete followed by the temperature of hot blast. A change in burden rate has been mainly reflected by a change in the weight of raw limestone in the burden. Considerable saving in coke rate is achieved by eliminating raw limestone from the burden through the use of higher quantity of super fluxed sinter. The productivity is adversely affected by the content of undersize fraction in lump ore as well as in sinter.
    On the basis of empirical equations, reported in the present work, salient approach for the improvement in the performance indices of the blast furnace has been mentioned in the text. lmprovement in the quality of sinter as well the granulometry of lump ore is important in this regard. The methodology to achieve such improvement has been outlined in the present paper.
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    Readers Who Read This Article Also Read

    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    2. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
    3. Suppression of the Formation of Large Pores in the Assimilated Parts of Sinter Produced Using Pisolitic Ores ISIJ International Vol.36(1996), No.11
  • Maximum Injection Rate of Fine Ore into Blast Furnace through Tuyeres

    pp. 677-684

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    DOI:10.2355/isijinternational.31.677

    In order to obtain the maximum fine ore injection rate, an experimental apparatus capable of simulating the heat transfer and reaction in the lower part of the blast furnace was built. This apparatus is 0.90m3 in inner volume, is a 90° sector in cross-section, is one-fifth of the actual blast furnace in height and is equipped with one tuyere.
    As a result of the fine ore injection through the burner which was inserted through the blow pipe, the maximum fine ore injection rates at which the desired deadman temperature can be maintained were experimentally determined as shown below. The maximum fine ore injection rate in the actual blast furnace is expected to be higher than those measured here.
    • The injection of the 0% prereduced fine ore alone is difficult.
    • About 70g/Nm3 for injection of the 0% prereduced fine ore mixed with the same amount of pulverized coal.
    • 175g/Nm3 for injection of the 60% prereduced fine ore alone.
    • About 115g/Nm3 for injection of the 60% prereduced fine ore mixed with the same amount of pulverized coal.
    x

    Readers Who Read This Article Also Read

    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    2. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
    3. Suppression of the Formation of Large Pores in the Assimilated Parts of Sinter Produced Using Pisolitic Ores ISIJ International Vol.36(1996), No.11
  • Equilibrium Partitions of Manganese and Phosphorus between BaO-BaF2 Melts and Carbon Saturated Fe-Mn Melts

    pp. 685-688

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    DOI:10.2355/isijinternational.31.685

    The phosphorus and manganese partition ratios between BaO-BaF2-MnO fluxes and Fe-Mn-Csatd. alloys were measured at temperatures ranging from 1473 to 1573K in a CO atmosphere.
    The phosphorus partition ratio increases with increasing BaO content of the fluxes. This ratio for the BaO-BaF2-MnO system is smaller than that for the BaO-BaF2 system because of the strong interaction between manganese and phosphorus in molten iron. The temperature dependence of the phosphorus partition ratio was found to decrease with increasing temperature. The effect of manganese on the phosphorus content of carbon saturated iron melts is also discussed.
    The manganese partition ratio increases with increasing BaO content of the fluxes and with decreasing temperature. The manganese oxide in fluxes is likely to behave as an acidic oxide for the BaO-BaF2 system where BaO acts as a strongly basic oxide.
  • Strip Quality of Highly Alloyed Metals by Twin Roll Casting

    pp. 689-695

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    DOI:10.2355/isijinternational.31.689

    The commercial success of twin roll casting, like of other strip castings, depends, largely upon the quality of its cast products. For quality improvement, various aspects of twin roll casting have been investigated. An on-line measurement of flow rate and strip thickness has proved that the charge of strip thickness at width center is proportional to the change of flow rate. A TV monitor system has shown that the pool surface on the cooling rolls repeats fluctuation of ±4mm due to melt feeding and roll rotation, causing the strip thickness variation of ±7%. Casting with different roll-sleeve thicknesses has shown that thinner sleeves produce convex strip and thicker sleeves produce concave strip. Strip temperature observation at the coiling stage has indicated that precipitation of σ phase makes austenitic stainless steels quite brittle.
    A sliding gate nozzle has been introduced to control the flow rate; cooling rolls with complicated sleeve profiles have been devised to control the roll crown; a secondary cooling with water jets has been applied to prevent σ phase precipitation. Consequently, stainless steels or Ni base alloys are being cast into commercial grades of overlay welding hoops.
  • Ultrasonic Prediction of r-value in Deep Drawing Steels

    pp. 696-705

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    DOI:10.2355/isijinternational.31.696

    The textures of five types of deep drawing steels were measured and analyzed using the series expansion method. Modul-r and electromagnetic acoustic (EMAT) techniques were employed to determine the elastic anisotropy in terms of the angular variation of Young's modulus and the ultrasonic velocities, respectively. The plastic anisotropy was assessed by measuring r-values as a function of inclination with respect to the rolling direction. The series expansion formalism was employed for predicting the elastic and plastic anisotropies from the initial texture data. Comparison with the experimental measurements of Young's modulus indicates that the so-called elastic energy method can accurately reproduce the elastic anisotropy if the single crystal elastic constants are appropriately chosen within their ranges of uncertainty. The angular variation of r-value in the rolling plane was calculated from the ODF coefficients by means of a relaxed constraint model (pancake version). The best quantitative agreement is obtained when the CRSS ratio for glide on the {112}‹111› and {110}‹111› slip systems is 1.0, 0.95 and 0.90 for the IF2, IF1 and AKDQ grades, respectively. The ODF coefficients of order greater than 4 were evaluated and calculated non-destructively from the anisotropy of the ultrasonic velocities of the lowest order symmetrical Lamb (S0) and shear horizontal (SH0) waves propagating in the rolling plane. The calculated pole figures based on the ODF coefficients obtained in this way are similar to those derived from complete X-ray data. It is shown that the plastic properties of commercial deep drawing steels are predicted more accurately when the 4th and 6th order ODF coefficients are employed than when only the 4th order ones are used.
  • Development of a New Low Carbon Low Alloy Steel Suited to be Clad with Stainless Steel

    pp. 706-711

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    DOI:10.2355/isijinternational.31.706

    A new steel containing low C and low Nb, Ti and N has been developed which is suited to be clad with austenitic stainless steel. The steel should have fine ferrite grains in the final stage in order to avoid an orange peel phenomenon in its subsequent plastic deformation. Various parameters affecting the resultant ferrite grain size of the steel have been investigated. Main factors favored to obtain fine ferrite grains are (1) Ti/N in atomic percent being 0.5 rather than 1.5, (2) high Nb and C contents for the steel annealed in γ-region, (3) annealing of the steel in α-region rather than in γ-region, (4) the faster cooling rate after the final annealing process. In accordance with these results, three possible ways to make steel having grains finer than 7 in JIS grain size number are proposed, and finally a low C, low Nb, Ti and N steels have been successfully clad which austenitic stainless steel on mill and laboratory scales with has shown no orange peel phenomenon in their subsequent plastic formings.
  • Some Aspects of lnclusion Characterization in Resulphurized HY-80 Steel

    pp. 712-720

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    DOI:10.2355/isijinternational.31.712

    Sulphide inclusions in HY-80 steels containing sulphur from 50 to 500 ppm especially prepared by resulphurization of commercial HY-80 steels, have been quantitatively characterized with regard to their type, size, shape and distribution using automatic image analysers. The formation of sulphide inclusion in HY-80 steel is discussed from thermodynamic considerations. It is seen that inclusion parameters such as volume fraction and aspect ratio increase linearly with the increase in sulphur content whereas the projected length varies non-linearly as a function of sulphur. The number of inclusion per unit area increases with increase in sulphur content. Correlation of charpy impact energy with these parameters shows that charpy energy decreases with increase in aspect ratio and projected length. The effects of the inclusion parameters on the impact energy are analysed in the light of Bilby's distribution model which unlike the other models, takes into account both volume fraction and aspect ratio of inclusions. The values predicted by the model are found to be in good agreement with the experimental results.
  • Optimal Chemical Composition in Fe-Cr-Ni Alloys for Ultra Grain Refining by Reversion from Deformation Induced Martensite

    pp. 721-727

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    DOI:10.2355/isijinternational.31.721

    A thermomechanical treatment, which applies reversion from deformation induced martensite (α') to ultra grain refining of austenite (γ), was proposed for metastable austenitic stainless steels. To determine optimal steels for the treatment, the effect of chamical composition on the γ-α' transformation behavior during cold rolling and the α'-γ reversion behavior by successive annealing was investigated in Fe-Cr-Ni ternary alloys. An ultra fine γ grain structure was obtained when steels satisfied the following three compositional conditions:
    (1) Metastable γ should be almost completely transformed to α' during cold rolling at room temperature. The amount of α' induced by 90% cold rolling can be estimated by the Ni equivalent (Ni+0.35Cr). For steels with the Ni equivalent of less than 16.0 mass%, over 90 vol% of γ transforms to α' during 90% cold rolling at room temperature.
    (2) Most of deformation induced α' must revert to γ again at relatively low temperatures where grain growth is difficult to occur. When the Cr equivalent (Cr-1.2Ni) is less than 4.0 mass%, most α' induced by the 90% cold rolling reverts to γ through 873K-0.6ks annealing. Retained α' is less than 10 vol%.
    (3) The Ms temperature of the reversed γ obtained through 873K-0.6ks annealing should be below room temperature. When the Ni equivalent (Ni+0.65Cr) of steels is more than 19.7 mass%, the reversed γ is stable at room temperature. For the Fe-Cr-Ni ternary alloys which satisfy these three conditions, an ultra fine γ grain structure might be obtained through the reversion from deformation induced α'. For example, γ grains of 0.5μm were observed in a 15.5%Cr-10%Ni steel which was subjected to 90% cold rolling and subsequent 873K-0.6ks annealing.
  • High Temperature Deformation Behavior of Titanium-Aluminide Based Gamma Plus Beta Microduplex Alloy

    pp. 728-737

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    DOI:10.2355/isijinternational.31.728

    A new type of microstructure has been developed by an optimum combination of macroalloying and thermomechanical processing in a high-purity gamma titanium-aluminide based ternary alloy: Ti-47at%Al-3at%Cr. The microstructure that is characterized by a microduplex structure of gamma and beta phases renders superplasticity to the alloy. A chromium enriched beta phase is formed by alloying of chromium as a beta stabilizing element by substitution of aluminum in the stoichiometric gamma composition. The beta phase of a body centered cubic structure is identified by crystallographic analyses with X-ray and electron diffraction and by compositional analyses with electron probe and energy dispersive X-ray spectroscopy. Thermomechanical processing induces precipitation of the beta phase along gamma grain boundaries. High temperature deformation behavior of the gamma plus beta microduplex alloy is studied in comparison with a fine grained binary stoichiometric gamma alloy. The microduplex alloy shows a total elogation of about 450% at an initial strain rate of 5.4×10–4 at 1473K, the strain rate sensitivity parameter being 0.57 far above 0.3 which is a criterion of superplasticity. Evolution of texture and microstructure is characterized for understanding of the mechanism operating in superplastic deformation. High temperature deformation structures of the microduplex alloy show no preferred orientation as an indication of random grain rotation. The beta phase is observed to spread along grain boundaries during deformation, contributing to promotion of the grain boundary sliding mechanism of superplasticity as well as to stabilization of the fine grained structure. Formation and coalescence of cavities at the interfaces of gamma and beta grains determine the limit of superplastic elongation.
  • Mechanical Properties and Aqueous Corrosion Behaviour of the Ferritic Fe-Cr-V Alloys

    pp. 738-743

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    DOI:10.2355/isijinternational.31.738

    Corrosion behaviour of the Fe-17Cr-(2-5)V and Fe-23Cr-(2-5)V alloy systems in 5% sulphuric, 5% hydrochloric and 0.5% sodium chloride solutions has been investigated by means of the immersion test and potentiodynamic measurements. Results are also given on the effect to Mo or Ni addition on the corrosion resistance of these alloy systems. Immersion test reveals that the additions of 2 and 5% V have little influence on inhibiting dissolution of the Fe-17Cr alloy in sulphuric and hydrochloric solutions. However, addition of 1% Mo to the Fe-17Cr-2V alloy has been shown to enhance resistance to corrosion in reducing acid solutions. Moreover, additions of 1-2% Ni to the Fe-17Cr-(2-5)V system also exhibit a similar inhibiting effect on alloy dissolution but it is less pronounced than with Mo addition. From cyclic polarization curves it is evident that the Fe-17Cr-(2-5)V system with or without Mo or Ni addition is subject to pitting corrosion due to its low breakdown potentials and large hysteresis loops. The immersion and potentiodynamic techniques have shown that the Fe-23Cr-3V-2Mo alloy exhibits the highest resistance to reducing acids and sodium chloride solution among the alloys studied.
  • Localized Coking on Austenitic Heat-resisting Steels in CO-H2 Mixtures at 923 K

    pp. 744-749

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    DOI:10.2355/isijinternational.31.744

    The coking behavior on the austenitic heat-resistant steels (SUS309S and SUS310S) and iron in CO-H2 mixtures at 923 K was studied. Two types of carbon, laminar carbon and filamentous carbon, deposited on iron in large amount, while only filamentous carbon slightly deposited on the high temperature steels because of the formation of noncatalytic chromium-rich carbides on the surface instead of laminar carbon. On the steels, filamentous carbon deposited at some defects such as pittings and cracks occurred on the carbide scale. Thus, the increase in such surface defects by a severe surface finishing caused the acceleration of filamentous carbon deposition. The deposition of filamentous carbon on the surface defects or the localized coking is probably due to the depletion of chromium or the enrichment of iron at the exposed subsurface and thereby to the formation of an more unstable carbide. The behavior of filamentous carbon deposition on the heat-resistant steels seems to be essentially the same as that on iron. That is, the formation and decomposition of unstable carbides such as Fe3C and (Fe, Cr)3C may be involved in the process of filamentous carbon deposition on both iron and the heat-resistant steels.
  • Mechanism for Beneficial Effect of Y2O3 Dispersion for Protective Coating

    pp. 750-752

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    DOI:10.2355/isijinternational.31.750

    Although the beneficial effect of Y2O3 dispersion against high-temperature oxidation has been recognized for many years, the mechanism of the effect is still obscure. Our previous works suggest that dispersed Y2O3 suppresses spalling of Al2O3 coating layer by trapping a detrimental impurity element S within the bulk phase. In this work analytical electron microscopy gave a very important evidence for the S trapping on MA956-0.52Y2O3 alloy.
    Then it was found that the penetration of alloying constituents such as Mn, Cr into Al2O3 coating layer was extensively lowered on alloys doped with a moderate amount of Y2O3. This is considered another beneficial effect of Y2O3 dispersion.
  • Reduction of lron Ore with Coal in Rotary Kiln Using Statistical Design of Experiments

    pp. 753-755

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    DOI:10.2355/isijinternational.31.753

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  1. blast furnace
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  5. inclusions
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  7. isij xafs
  8. joo hyun park
  9. mold flux, b2o3
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