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

ISIJ International Vol. 35 (1995), No. 11

  • Zinc Recovery from Zinc-bearing Dusts by Use of Sensible Heat of Hot Metal

    pp. 1323-1330

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    DOI:10.2355/isijinternational.35.1323

    In order to develop a zinc recovery process from zinc-bearing dusts generated from ironmaking and steelmaking plants, fundamental and commercial scale experiments were carried out. Zinc-bearing dusts were mixed with cement and fine coke, and agglomerated as pellets or briquettes. These agglomerates were sharged into hot metal discharged from a commercial blast furnace. These tests indicated that zinc in the agglomerates was mostly vaporized, and the vaporized zinc was condensed in the collected dusts as zinc oxide. During the operation, a drop in the temperature of the hot metal was evaluated to be less than 10°C compared to the case by no charging.
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    2. Determination of Aluminum Concentration in Molten Zinc by the E.M.F. Method Using Zirconia Solid Electrolyte ISIJ International Vol.35(1995), No.5
    3. Structure of Electrodeposited Zn-Fe Alloy in the Zinc Rich Region ISIJ International Vol.32(1992), No.9
  • Reduction of Siliceous Manganese Ore by Graphite

    pp. 1331-1339

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    DOI:10.2355/isijinternational.35.1331

    Reduction of siliceous manganese ore containing 41.0 wt%Mn and 11.0 wt%SiO2 by graphite has been studied by the measurement of weight loss in argon atmosphere at 900, 1200 and 1400°C and following by X-ray diffraction and Microprobe analyses. The ore was sized to –150+53 μm and preliminary calcined at 1000°C in argon to ensure all weight loss in the experiments was due to reduction of the oxides present. The graphite was in the size fraction of –300+100 μm.
    Reduction extent was calculated relative to 100% of iron and manganese reduction. About 6% of reduction was observed after 2 h at 900°C and 35% after 2 h at 1200°C; 132% of reduction was found after 6 h exposure at 1400°C, this was due to silica reduction.
    Reduction at 900°C was limited to the reduction of iron oxides to FeO. Two reduction stages were distinguished at 1200 and 1400°C. During the first stage which extended to about 25% at both 1200 and 1400°C for 4-6 min iron oxides reduce to metallic iron and manganese oxides to MnO. It is suggested that at this stage oxides are reduced by CO gas. The second stage is the reduction of MnO to Mn and occurs via carbon in the metallic phase. This stage is suggested to be controlled by the diffusion of MnO in the solid ore at 1200°C and in the liquid phase at 1400°C. Slow rate of manganese ore reduction observed in the experiments may be attributed to the relatively high silica content in the ore.
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    1. The δ to γ Transition in Fe-Cr-Ni Alloys during Laser Treatment ISIJ International Vol.37(1997), No.7
    2. The Management of Research and Technology in the German Steel Industry with Respect to the European Union ISIJ International Vol.38(1998), No.9
    3. Analysis of Molten Steel Flow in Slab Continuous Caster Mold ISIJ International Vol.34(1994), No.3
  • Technology for Granulating Coke Breeze by Centrifugal Rolling Type Pelletizer and Effect of Granulated Coke Breeze on Sintering Operation

    pp. 1340-1347

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    DOI:10.2355/isijinternational.35.1340

    Coke breeze was granulated by a centrifugal rolling type pelletizer which was operated at a Froude number (Fr) that is more than 102 times that for the conventional drum mixer. The effects of the coke breeze granulated by this new technology on the sintering opetation, the granulation of raw mix for sintering, and the quality of sinter were quantitatively studied through sintering pot test and plant test at Nagoya No. 2 Sintering Plant. As a result, the following findings were obtained:
    (1) In the coke breeze granulation test, the centrifugal rolling type pelletizer could not only granulate fine coke breeze but also cause ultra-fine coke particles to penetrate into coarser particles, while preventing the granulated particles from becoming excessively coarse.
    (2) In the sintering pot test and sintering plant test, it was clarified that granulated coke breeze became the nuclei of quasi-particles of the raw mix for sintering and then promoted the granulation of other raw materials in the iron ore sintering process.
    (3) It was confirmed that this new technology could decrease NOx emissions by reducing the ratio of fine particles in coke breeze. NOx emissions could be further reduced by the addition of quick lime. It was also clarified that the reducibility of sinter was improved.
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    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
  • Measurement of the Volumetic Mass Transfer Coefficient of Gas-stirred Vessel under Reduced Pressure

    pp. 1348-1353

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    DOI:10.2355/isijinternational.35.1348

    The behavior of bubbles in a vessel under reduced pressure was observed and the volumetric mass transfer coefficient was measured using a water model. The average diameter of the bubbles immediately after breaking away from the orifice increased with increasing gas flow rate corrected by the pressure at the orifice. An empirical equation for the volumetric mass transfer coefficients under normal and reduced pressures was developed, which can represent previous work using a water model.
  • X-ray Fluoroscopic Observation of Bubble Characteristics in a Molten Iron Bath

    pp. 1354-1361

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    DOI:10.2355/isijinternational.35.1354

    The formation of bubbles at a nozzle and subsequent rising behavior of them in a molten iron bath at 1250°C were observed using a high-voltage X-ray fluoroscope and a high-speed video camera. The frequency of bubble formation at the nozzle exit, the mean bubble diameter and the mean bubble rising velocity were obtained for a side range of injected argon gas flow rate. Empirical correlations of these quantities were proposed and compared with previously published experimental data and empirical correlations.
    It has been commonly believed that the frequency of bubble formation at a nozzle placed in a molten metal bath depends solely on the gas flow rate and the outer diameter of the nozzle when the gas flow rate is relatively high and the wettability between the nozzle material and the molten metal is bad. The present experimental results, however, revealed that the frequency of bubble formation has a close relationship not with the outer diameter but with the inner diameter of the nozzle for a higher gas flow rate. Furthermore, the bubble frequency depended on the gas flow rate and the physical properties of gas and molten metal. The critical gas flow rate for the initiation of small bubbles due to disintegration of large bubbles coming from the nozzle exit was approximately 60 cm3/s under the present experimental conditions. The bubble behavior near the bath surface also was made clear.
  • EMF Sensor Control in Vacuum Decarburization and Deoxidation of Steel Melts

    pp. 1362-1367

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    DOI:10.2355/isijinternational.35.1362

    Newly designed electrochemical sensors were used for continuous measurements of oxygen activity in 4 kg vacuum induction melts at 1600°C. It is shown that the activity of oxygen can be recorded over at least 3 h under a vacuum of 0.001 bar. A good agreement between the values derived from EMF measurements and those from chemical analysis was obtained. The rate of decarburization is strongly affected by the initial concentration of oxygen in the melt. He process is controlled either by diffusion of carbon to the interface of melt/gas, if the melt is sufficiently supplied with oxygen, or by oxygen transfer to the boundary of melt/gas at the beginning of decarburization. The resulting mass transfer coefficients or carbon and oxygen are 0.01 cm/s, respectively.
  • Shape Control of Inclusions in High Nickel Content Steel

    pp. 1368-1373

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    DOI:10.2355/isijinternational.35.1368

    To control the inclusion shape of iron-nickel alloys, inclusion compositions were investigated in 2 kg scale experiments on deoxidation with flux. The effect of nickel content on deoxidation equilibrium of silicon or aluminum was discussed. Most of inclusions were considered to be secondary inclusions during cooling or solidification. Using the thermodynamic data, inclusion compositions were estimated. The accuracy of the estimation is good, and it proved to be possible to estimate the inclusion compositions.
  • Effect of Stirring Energy and Rate of Oxygen Supply on the Rate of Hot Metal Dephosphorization

    pp. 1374-1380

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    DOI:10.2355/isijinternational.35.1374

    Study was made on desiliconization and dephosphorization reaction kinetics at various size equipments. Coupled reaction model was employed to analyse rate determining step of desiliconization and dephosphorization reaction.
    In the case of desiliconization reaction, mass transfer process in hot metal phase determines the reaction rate. On the other hand, dephosphorization rate is controlled by mass transfer process both in hot metal and slag phase. Mass-transfer coefficient in hot metal phase km proportionally increased with 0.7 power of parameter ε/dC2, independently on the equipment size, where, ε, dC is stirring energy of hot metal and the diameter of the vessel, respectively.
    Apparent rate constant of dephosphorization kP'=ln([%P]i/[%P]f)/tf increased with increase in stirring energy ε' and rate of oxygen supply VO2 under the optimum relationship between ε' and VO2 which was predicted by model calculations, where [%P]i and [%P]f is initial and final phosphorus content and tf, refining time. This optimum relationship was expressed as the empirical relation, ε'=1.51VO22+3.31 VO2 under the condition of this study.
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  • Thermal Plasma Chemical Vapor Deposition of SiC

    pp. 1381-1387

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    DOI:10.2355/isijinternational.35.1381

    To develop a new surface modification capable of controlling the film quality at a high deposition rate, a Chemical Vapor Deposition (CVD) process using thermal plasma jet was studied. In this work, a method of most suitably supplying reaction gas into thermal plasma jet which was a high velocity flow was examined using spectral analysis by a two-dimensional imaging spectrometer. A SiC film was deposited on graphite using SiCl4 and CH4 as reaction gases and Ar-10%H2 gases as plasma forming gases. The maximum deposition rate of 2.78×10-7 m/sec was obtained by supplying each of the above reaction gases in an amount of 2.67×10-5 m3/sec. The deposited SiC film was a columnar structure, the hardness being about HV 2400.
  • Alloying Reactions in Hot Dip Galvanizing and Galvannealing Processes

    pp. 1388-1393

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    DOI:10.2355/isijinternational.35.1388

    The iron-zinc alloying reactions which take place during hot dip galvanizing and galvannealing processes were investigated, with special reference to the formation and growth behavior of iron-zinc intermetallic compounds. The SEM observation and X-ray diffraction analysis of the intermetallic compounds which had formed on laboratory galvanized Ti stabilized interstitial-free steel and on low carbon aluminum killed steel sheets showed that there were two types of elementary iron-zinc alloying reactions; one was the formation of ζ and δ, crystals and another was so-called outburst reaction.
    The ζ crystal nucleated on the Fe-Al intermetallic compound which had been formed on the steel surface, and grew into the melt as a single phase crystal. Simultaneously, the outburst structure was generated as a result of the direct reaction between iron and molten zinc, and grew as a multiple phase structure (ζ, δ1 and Γ phases). The ζ phase was generated at the isothermal galvannealing temperature of less than 773 K, and it was explained in terms of the iron-zinc equilibrium phase diagram (peritectic temperature of ζ phase). The effects of solute element in steel on the thickness of Γ phase were explained by its suppression effect toward the outburst reaction.
  • Influence of Previous Structure on Laser Surface Hardening of AISI 1045 Steel

    pp. 1394-1399

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    DOI:10.2355/isijinternational.35.1394

    The effect of laser surface hardening was studied in an AISI 1045 steel with different microstructures: ferrite and pearlite, or with carbides dispersed in the ferritic matrix produced by martensite tempering at 180, 450, 600 and 660°C.
    The laser treatments were carried out working with a 10×10 mm square beam of uniform power density and 1.5, 2.5 and 5 kW output power. The scan rates permitted temperatures to range from those at the austenitization start to the melting point of the material.
    The depths of the zones of affected material were revealed by metallographic observation and Vickers hardness measurement. The results suggest that the initial structure of the steel has a considerable influence on laser surface hardening effect. The differences are manifested in the depths of the distinct heat affected zones and in the obtained microstructures.
  • Development of 12%CrNb Steel for Heavy Duty Gas Turbine Discs

    pp. 1400-1406

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    DOI:10.2355/isijinternational.35.1400

    Effect of adding elements on creep rupture strength and toughness for heat resistant 12%Cr steel of 1300°C class gas turbine disc was investigated. Creep rupture strength was increased by addition of Mo, W, V, Nb, and N. It was found that the addition of Nb causes a significant increase of creep rupture strength due to fine dispersion of NbC and of ductility due to grain refining. Chemical composition of 12Cr-2.5Ni-2Mo-0.2V-0.08Nb-N steel is determined for gas turbine disc application. Preparation of real scale disc was carried out by electro-slag remelting process in order to avoid the segregation of adding elements in ingot. It is resulted that the mechanical properties of real scale disc specimen show the equivalent properties of small specimens. The steel discs for gas turbine were manufactured from the new steel.
  • Warm Stretch-formability of TRIP-aided Dual-phase Sheet Steels

    pp. 1407-1414

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    DOI:10.2355/isijinternational.35.1407

    The effects of retained austenite parameters (stability and volume fraction) and second phase morphology ("a network structure: TYPE I" and "an isolated fine and acicular one: TYPE II") on a warm stretch-formability of high-strength TRIP-aided dual-phase sheet steels were investigated. Good warm stretch-formability, i.e., large stretch-height and low stretching load, was achieved particularly in the steels with the second phase morphology of TYPE II, in which the retained austenite islands were nearly isolated in the ferrite matrix away from bainite islands. Significant improvement of the stretch-height by warm forming was botained in the steels containing a large amount of retained austenite with low carbon concentration. Optimum forming temperature Tp corresponding to the maximum stretch-height was between 20 and 225°C and increased linearly with increasing the Ms of the retained austenite. The Tp rose by 10-30°C compared to that of total elongation due to a high applied mean normal stress, except for some steels with the TYPE II morphology.
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  • Assessment of the Mobilities of Cr, Fe and Ni in bcc Cr-Fe-Ni Alloys

    pp. 1415-1421

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    DOI:10.2355/isijinternational.35.1415

    Experimental data on the diffusional mobilities of Cr, Fe and Ni in bcc Cr-Fe-Ni alloys are assessed by means of a model which takes the effect of a ferromagnetic transition in multicomponent alloys into account. Comparison between experimental data and calculations are made and a satisfactory agreement is found. A set of parameters describing the variations of the mobilities with temperature and composition are given.
  • Effects of Copper, Nickel, Chromium and Tin on Mechanical Properties of Titanium-bearing Extralow-carbon Steel Sheets

    pp. 1422-1429

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    DOI:10.2355/isijinternational.35.1422

    The effects of copper, nickel, chromium and tin additions on the mechanical properties of extralow-carbon titanium-bearing continuous annealed steel sheets were studied. The following are the findings obtained:
    (1) Copper and chromium additions up to approximately 0.2% each increased tensile strength and decreased total elongation and the r value.
    (2) With the specimens each containing 0.2% copper and 0.2% chromium, lowering the slab reheating temperature to 1050°C decreased tensile strength and increased total elongation and the r value.
    (3) Nickel addition up to 0.12% produced no significant effect on tensile properties and the r value.
    (4) Tin addition up to 0.085% increased tensile strength and decreased total elongation and the r value. With the specimens containing tin, lowering the slab reheating temperature did not improve their total elongation and r value.
    (5) The effects of copper, nickel, chromium and tin contents on mechanical properties proved to be proportional to the difference in the atomic radius between iron and these allowing elements.
    (6) Copper, nickel, chromium and tin proved to produce different effects on the r value. With the specimens containing copper, nickel and chromium having slightly larger atomic radii than that of iron, lowering the slab reheating temperature improved their r value. With the specimens containing tin having a significantly larger atomic radius than that of iron, by comparison, lowering the slab reheating temperature produced only a small effect.

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