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

Tetsu-to-Hagané Vol. 78 (1992), No. 5

  • Challenge the Long Span Bridges

    pp. 689-696

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  • Measures for Carbon Dioxide Problem and Utilization of Energy

    pp. 697-705

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  • Material Problems in High Temperature Corrosive Environments and Their Solution by Surface Technologies

    pp. 706-713

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  • Dephosphorization of Molten Carbon Saturated Iron with CaO-FeCl2 Flux

    pp. 714-721

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    Dephosphorization of molten carbon saturated iron with CaO-FeCl2 flux was investigated in a laboratory scale test.
    By using CaO-FeCl2 flux of 100 kg/t, 90% dephosphorization is possible together with desulphurization of 8090% when the molten carbon saturated iron has silicon, manganese and chromium content less than 0.05%, respectively.
    In a graphite crucible test, dephosphorization of 60% is achieved even when molten carbon saturated iron has 1618% chromium content.
    The dephosphorization with CaO-FeCl2 flux is considered to be due to oxidation with (FeO) which is formed by the reaction between CaO and FeCl2. This is similar to the results obtained using CaO-CaCl2 FeO flux.
  • Improvement of Dephosphorization of Hot Metal by Preventing Rephosphorization from CaO-based Slag

    pp. 722-729

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    In order to improve dephosphorization, rephosphorization behavior of hot metal which contacts with CaO-FetO-SiO2-CaF2-P2O5 slag has been studied at 1350°C.
    The results obtained in this work are summarized as follows ;
    1) The rate of rephosphorization in Ar proceeds faster than that in air.
    2) The content of (FetO) in slag required to prevent rephosphorization is about 1% for slag with CaO/SiO2 of 4.66, and is about 2-3% for slag with CaO/SiO2 of 2.51.
    3) In dephosphorization process using injection method, addition of iron oxide to top slag, which increase (FetO) contents in slag, is quite important for improving dephosphorization.
    4) In dephosphorization of hot metal, the value of (T. Fe) is not available for index of oxygen potential in slag. Because the slag contains much iron particle with micron size. Therefore, the particle must be removed chemically before analyzing.
  • Effect of Calcination Conditions on the Reactivities of Burnt Dolomite with Water and Molten FeO-SiO2 Slag

    pp. 730-737

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    In steelmaking processes, slag formation in a converter is always a matter of interest. This study is focused on two kinds of dolomite produced at different areas in Japan. These dolomites were calcined in a laboratory furnace over the temperature range from 1073 K to 1473 K for two hours, and served to immersion test into water and molten FeO-SiO2 slag.
    The reaction behavior of burnt dolomites with water and the molten slag is characterized by two stages. One is the disintegration stage of dolomite, which is controlled by cracks due to the shrinkage of thermal decomposition during calcination. The other is the dissolution stage of each disintegrated particles. The important factor of this stage is the clearances among micro grains produced by the reaction during calcination.
    The disintegration stage is affected by grain size of raw dolomite and calcination temperature, but, the effect of grain size did not appear so clear in the slag because of intensive erosion ability of the slag.
    The dissolution rate decreases with an increase of the calcination temperature in the same way in both cases of the reaction with water and with the molten slag. This is because the micro grain combines with adjacent one to grow larger.
  • Video Image Analysis of Mixing Flow in a Cylindrical Vessel Agitated by a Bottom Blowing Bubbling Jet

    pp. 738-744

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    The Particle Tracking Velocimetry ( PTV ), which is one of the quantitative flow visualization techniques, enables to measure both instantaneous velocity distributions and traveling paths of fluid elements in relation with the condition of the whole flow field. And hence the technique is believed to become a useful tool for the measurement of mixing flows.
    In the present experiment, the binary correlation method, one of the PTV algorithms, is used in the measurement of the strong mixing flow in a cylindrical bath which is agitated by a bubbling jet from the bottom. The distributions of liquid phase such as instantaneous or short-time averaged velocity and those of RMS values of fluctuation are measured. Also velocities and sizes of rising bubbles are simultaneously measured.
  • Mechanism of Bubble Disintegration and Acceleration of Gas-Liquid Reaction with Ultrasonic Vibrating Nozzle in Water Model Experiment

    pp. 745-752

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    In the previous paper, it has been shown that the bubbles in water are disintegrated and the gas-liquid reaction is accelerated by applying ultrasonic vibration to the injection nozzle. In the present paper, the mechanisms of bubble disintegration and reaction acceleration have been discussed by examining bubble dispersion phenomena with the aid of electroresistivity probe and CO2 absorption experiment. The results were summarized as follows;
    (1) The bubble dispersion zone was not changed by applying ultrasonic vibration. The bubble rising velocity did not increase so much. The mean bubble diameter decreased to one half of that without ultrasonic vibration.
    (2) The gas column was formed in front of nozzle top by applying ultrasonic vibration. The surface of gas column vibrated violently. The fine bubbles were formed from the surface.
    (3) Acceleration of CO2 absorption could not be simply explained by the increase in interfacial area caused by bubble disintegration. Absorption was also accelerated at the nozzle top, because of the violent vibration of gas column surface.
    (4) Bubbles were disintegrated finer and CO2 absorption rate was larger as the power of ultrasonic vibration increased.
  • Flow Control of Liquid Iron by Magnetic Shield in a High-frequency Induction Furnace

    pp. 753-760

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    Flow control of liquid iron in a high-frequency induction furnace was carried out by using the magnetic shield for the frequency range from 30 kHz to 200 kHz. Several types of graphite shield with different resistivities (ρeff) were used for the experiments. Magnetic flux densities (Bz) were measured along the axis of the induction coil (90 mm ID, 140 mm height, 15 turns), and also the Joule's heats ( W) generated in the shields were measured. It was found that the degree of suppression of Bz near the shield and the value of W changed widely with ρeff and frequency (f). And then the experiment on the dissolution of graphite rod in liquid iron was made at 1 673 K to obtain the local and average mass-transfer coefficients (κLz and κL) which depend on the flow intensity. It was found that the values of κLz and κL varied widely with ρeff as well as f.
    The mutual inductance model was used for the analysis on the electromagnetic field in the furnace. Calculated values of Bz and W were in good agreement with the observed ones. The Navier-Stokes' equation and the conservation equation of carbon in liquid iron were solved numerically under laminar flow condition. Calculated values of κLz were consistent with the observed ones.
  • Analysis of Continuous Casting Powder Entrapping Phenomena by Water-model Experiments

    pp. 761-766

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    Mold-powder entrapping brings a serious problem of steel sheet defect caused by inclusion.
    It is caused by moldmeniscus flow, immersionnozzle Argon bubble burst in mold meniscus or sacking by voltex near the immersionnozzle. The present paper studies the effect of continuous casting condition on voltex growth by the watermodel experiment.
    The voltex growth is found to be strongly affected by maximun flowrate and immersionnozzle depth, and partially affected by powder viscosity.
    It is found to be little affected by mold meniscus velocity and immersionnozzle shape.
  • Numerical Analysis for Initial Stage of Rapid Solidification of 18Cr-8Ni Stainless Steel

    pp. 767-773

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    The initial stage of the rapid solidification of 18Cr-8Ni stainless steel has been numerically analysed using the cooling curves at the sample surface obtained in the experiments. Heat transfer coefficient between the chill substrate and the samples is determined by fitting the calculated cooling curves to experimental ones.
    In the vicinity of the surface, there exists the region where growth rate and temperature gradient are very large. The length of the region is nearly equal to that of the initial solidification structure of samples. The solidification conditions in the sample are estimated and the relation between secondary dendrite arm spacing and cooling rate is obtained.
  • Determination of Micro Trace Oxygen in High Purity Iron with the Inert Gas Fusion Method

    pp. 774-781

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    Method of the determination of micro trace oxygen ( ppm level ) in the high purity iron has been studied cooperatively by 14 member laboratories in the Chemical Characterization Sub-committee, 19th Committee ( steel making), Japan Society for Promotion of Science.
    The purposes of this study were set in the following focuses,
    1) Improvement of analytical precision.
    2) Clarification of detectable limit for oxygen determination with inert gas fusion method.
    3) Establishment of sample pretreatment technique.
    Two types of high purity iron samples ( oxygen content :<3 ppm and 5 ppm 10 ppm) were prepared at the Institute for Material Reseach, Tohoku University.
    Purities of these samples were respectively 99.995% except of carbon used to killing agent.
    The oxygen contents in the surface layer of the sample gave an considerable increase to the analytical values for ppm-level analysis.
    So, pretreatment method of the samples were mainly studied in details.
    As the results, the pickling method with H2O2+HF aq. solution was established.
    The results obtained by the recommended procedure were compared with He3+ particles activation analytical values and the precisions of the both oxygen values in each sample were satisfactory.
    The detectable limit of oxygen by the inert gas fusion method was about 1.5 ppm.
  • Development of a Quenching Roll to Control the Thermal Crown and the Effect on Uniform Cooling of a Strip

    pp. 782-789

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    Roll quenching is one of the cooling methods of a strip in a continuous annealing line. The strip is cooled by contact with the roll which is cooled by a coolant ( usually water) from the inside. Applying this method, it is important to unify the temperature of the strip transversely and to prevent shape defects of the strip when the strip is in contact with the roll.
    This report describes numerical analysis of the thermal crown on the quenching roll, as well as, the new structure of the quenching roll which restrains the thermal crown in order to prevent non-uniform contact between the strip and the roll. The newly developed roll is structured that the outer sleeve with screw-shaped waterways inside, is put on the inner sleeve using a shrink fit method. Thermal expansion of the roll sleeve which is heated by the strip is canceled by the initial strain of the shrink fitting.
    Applying this quenching roll and correcting the shape defects before cooling are very efficient to cool a strip uniformly and obtain a flat strip.
  • Generalized Nb Carbonitride Precipitation Model Applicable to Extra Low Carbon Steel

    pp. 790-797

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    The isothermal precipitation behavior of Nb(C, N) in austenite has been investigated using steels of different carbon contents. The observed progress of the precipitation in extra low carbon steel ismuch faster and size of the precipitates is apparently larger than those in steels with higher carbon content even though their supersaturations are the same. To explain this phenomenon, the local equilibrium at the austenite/Nb( C, N) interface has been introduced into the classical nucleation theory and the spherical growth theory, and a generalized precipitation model has been proposed which can predict the precipitation behavior of extra low carbon steels as well as that of HSLA steels. As a conclusion, this study clealy shows that the kinetics of MC-type precipitation is influenced not only by the precipitate-forming atomic product, M·C, but also by its ratio, M/C.
  • Effects of Alloying Elements on Mechanical Properties of 3Cr-Mo-W Steels for Heavy Sectional High Temperature and High Pressure Vessel

    pp. 798-805

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    Development of heavy sectional pressure vessel steels which are applicable to higher pressure and higher temperature hydrogen environment, is much in demand in recent years. In this study, creep rupture properties, temper embrittlement susceptibility and resistance to hydrogen attack were investigated in 3Cr-Mo-W steels which was developed by modifing 21/4Cr-1Mo steel mainly in order to suppress hydrogen attack. As results, effects of V, W, Ni and Cr on mechanical properties and precipitation behavior of carbides which affect creep rupture properties and hydrogen attack susceptibility were revealed. For instance, V addition increased creep rupture strength through precipitation of fine VC carbides, Cr decreased an amount of VC, replacing a part of Mo with equivalent W stimulated the precipitation of M6C carbides and increased creep rupture strength. Through autoradiography of B10, it was found that 10 ppm boron addition suppressed effectively the transformation of austenite to ferrite and temper embrittlement due to its grain boundary segregation. It was shown that 3Cr-0.7Mo-1.3W-0.3V-0.03Nb-B steel yielded high creep rupture strength together with good resistance to temper embrittlement and hydrogen attack.
  • Effects of Alloying Elements and Heat Treatments on Hardness and Magnetic Permeability of 18Mn-5Cr-2Ni-C Steels

    pp. 806-813

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    In order to obtain the basic information for developing high hardness non-magnetic steel, the effects of alloying elements and heat treatment on various hardening mechanisms and magnetic permiability were investigated in 18Mn-5Cr-2Ni-C steels. Large work hardening was not always found in steels which were presumed to have low stacking fault energy. This fact could be qualitatively explained by the relationship between the formation mechanism of deformation twin and pre-existing dislocation configuration, and by the effect of SFE on a breaking down of Interstitial-Substitutional complexes. Vanadium increased hardness effectively through precipitation of fine V4C3 carbide, whereas it reduced an amount of ε martensite produced by cold working. Silicon addition enhanced the precipitation of V4C3 and strain aging. The increase in hardness could be kept even after the reversed transformation of ε martensite. In high C steels, per meability was increased when M3C carbide precipitated. Through suitable heat treatment, a steel with high hardness around HV 650 and very low permeability could be obtained.
  • Creep-Rupture Life and Alloy Manufacturing Criterion Related to the Solidification and Precipitation Temperatures in Nickel-based Single Crystal Superalloys

    pp. 814-820

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    The solidification and precipitation temperatures were measured and were correlated with the creeprupture property and the microstructure of nickel-based single crystal superalloys. For three Co-content varying Ni-10 mol% Cr-12 mol% Al-1.5 mol% Ti-Ta-W-Mo-0.25 mol% Re-0/4.5/9.0 mol% Co alloys and also for three Cr-content varying Ni-10/13/16 mol% Cr-12 mol% Al-1.2 mol%Ti-Ta-W-Mo alloys, the liquidus, solidus, eutectic γ'precipitation and γ'solvus temperatures were determined by differential thermal analysis (DTA). It was found that as the Co and Cr contents increased, the γ'solvus temperature decreased and there was the attendant decrease in the volume fraction of the γ' phase in the alloys. In response to these changes the creep-rupture lives decreased with the Co and Cr contents. These results imply that the γ' solvus temperature is an indication of the creep-rupture lives of the nickel-based superalloys. In addition, a manufacturing condition for single-crystal growth was estimated from the measured solidification temperature range of alloys. All of the six alloys were shown to meet this condition, and their single crystals were grown successfully in agreement with the estimation.
  • Alloying Effects of Cr and Re on the Hot-corrosion of Nickel-based Single Crystal Superalloys Coated with a Na2SO4-NaCl Salt

    pp. 821-828

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    The alloying effect of chromium and rhenium was investigated on the hot-corrosion resistance of nickelbased single crystal superalloys. Using a conventional thermo-gravimetric method, hot-corrosion resistance to the Na2SO4-NaCl salt environment was measured with a variety of alloys, Ni-(916)mol%Cr-12 mol%Al-(1.22.0)mol%Ti-(1.12.7)mol%Ta-(1.23.8)mol%W-(01.0)mol%Mo-(01.0)mol%Re.
    Hot-corrosion resistance was shown to be improved significantly with increasing chromium content in the alloys. For example, a hot-corrosion index which was defined as the weight gain of the specimen exposed for 72 ks to the salt, was reduced to nearly nil in the 16 mol% Cr alloys. This result was interpreted as due to the existence of a corrosion product layer containing Cr, Al, Ni, O and S. This layer formed in the interface between the base alloy and the salt was very efficient in suppressing the hot-corrosion due to a basic-fluxing mechanism. Similarly, it was found that the addition of a small amount of rhenium up to 0.40.5 mol% could improve hot-corrosion resistance remarkably.
  • Oxidation Behaviors of Pure Titanium at High Temperatures in Ar-H2O Atmospheres

    pp. 829-836

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    The oxidation behaviors of pure titanium were investigated in the temperature range of 1 000 K to 1 300 K in Ar-H2O gas mixtures which contented 1 or 10 percent of water vapor.
    Optical microscopy, electron probe microanalyses and powder X-ray measurements on the oxide scales formed during oxidation indicate that their structures were nearly independent of temperatures and atmospheres employed ; the scales consisting of two layers, external one and internal one, have the rutile structure.
    The parabolic rate laws are confirmed on growths of scale layers and the permeation depth of oxygens in titanium with the apparent activation energies, 238-261, 260-261 and 209 kJ/mol, respectively. The rate determining diffusion species in these oxidation-processes were discussed.
  • Effect of Microstruture on Sustained Load Cracking Behavior of Ti-6Al-4V Alloy

    pp. 837-844

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    Sustained load cracking behavior of Ti-6Al-4V was studied by constant load testings and constant cross head speed tensile testings using compact tension specimens for four different microstructures. Annealed specimens and duplex annealed specimens showed stable crack growth without incubation time during constant load testings for initial K values which were considerably low, compared with KIC, while beta annealed specimens and solution treated and aged specimens showed no such behaviors. In the stable crack growth, the rate of COD change decreased with decreasing the load. Fractography and micrography revealed that the stable crack propagation occurred with quasi-cleavage fracture of primary alpha phase. In constant cross head speed tensile testings, the fracture toughness of annealed specimen decreased with decreasing the cross head speed, while beta annealed specimens showed no such behavior. The stable crack growth of annealed specimen initiated at a stress intensity factor about half of KIC at the lowest cross head speed.

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  1. blast furnace
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  6. a structurally-based viscosity model of the fully liquid slags in the cao-mgo-al2o3-feo-sio2 system
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