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

Tetsu-to-Hagané Vol. 73 (1987), No. 2

  • Present Status of Electroslag Remelting Process

    pp. 233-241

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    Readers Who Read This Article Also Read

    1. Internal Corrosion of Food Cans Tetsu-to-Hagané Vol.73(1987), No.3
    2. ASEANで成功する方法(?) Tetsu-to-Hagané Vol.74(1988), No.12
    3. Development of Continuous Casting Technology for Special Steel Wire Rod and Bar Tetsu-to-Hagané Vol.74(1988), No.7
  • Effect of the Surface Treatment on the Wear Resistance of the Iron and Steels

    pp. 242-251

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  • Corrosion Protection Technology of Marine Steel Structure

    pp. 252-258

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  • Activity Report of Surface Analysis Subcommittee of the Iron and Steel Analysis Committee, the Joint Research Society of ISIJ

    pp. 259-274

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  • Preferential Removal of Si, Nb and Mn from Pig Iron Containing Nb

    pp. 275-282

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    The recovery of Nb and Mn for mineral resources, P for a fertilizer, and the production of iron and steel of good quality from a pig iron containing Nb in China have been studied. This report describes the first preferential removal of Si over Nb, and the preferential removal of Nb over Mn, or, the preferential removal of Mn over Nb from the pig iron after desiliconization, bearing in mind a multi-stage continuous refining process, in order to increase the content of an aimed element in the slag recovered. The oxidation rates of elements in pig iron of 1 kg in a graphite crucible were measured by adding Fe2O3, CaO, Na2CO3, and B2O3 onto the bath. The effects of temperature, oxygen feeding rate (Fe2O3 g/5 min), and weight of those reagents upon the oxidation rates were discussed. The results obtained are as follows;
    (1) The preferential removal of Si over Nb was accomplished with an optimum amount of Fe2O3 at high temperatures. In this case, the reduction of Nb2O5 in slag formed by C in molten pig iron was important.
    (2) The preferential removal of Nb over Mn from the pig iron after desiliconization was achieved with a basic flux, CaO or Na2CO3.
    (3) The preferential removal of Mn over Nb from the pig iron after desiliconization was realized with an acid flux, B2O3.
  • Removal of Boron from Molten Pig Iron and Dissolution of B2O3 Slag into Water

    pp. 283-288

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    In order to remove B in pig iron as much as possible, the oxidation rates of elements in molten pig iron were measured by adding Fe2O3, CaO, Na2CO3, BaO, BaCO3 and Li2CO3 onto the bath: In addition, to recover B2O3 from slag and to increase MnO content in slag, the dissolution rate of B2O3 in slag into the distilled water or HCI solutions was estimated. The results obtained are as follows;
    (1) The removal ratio of B from pig iron was high at lower temperatures without a basic flux. However, a basic flux should be used to prevent B2O3 from reducing because the reduction rate of B2O3 was high at higher temperatures.
    (2) The removal ratio of B was high under the same conditions of lower temperature, higher oxidation atmosphere, and higher slag basicity as those of dephosphorization.
    (3) The dissolution ratio of B2O3 in slag into the distilled water at 100 °C decreased as the increase of content of MnO, FeO and SiO2 in slag. B2O3 in slag dissolved completely into the HCI solutions at 50 °C above 0.25 N concentration.
  • Measurement of Heat Transfer Coefficient between Melt and Chill

    pp. 289-296

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    A method for the measurement of the heat transfer coefficient between melt and chill during rapid solidification at about 103°C/s is proposed. Melt of tin with different superheat was dropped and solidified on a cylindrical chill of brass, stainless steel, nickel or chromium plated brass. Average values of the solidification time and the thickness of samples are obtained for each superheat, and then they are extrapolated to zero superheat.
    By using these data at zero superheat, the value of heat transfer coefficient for each chill is calculated analytically. The obtained values for chill of brass, stainless steel, chromium plated brass and nickel plated brass are 0.70, 0.28, 0.39 and 0.33 cal/cm2°C/s, respectively. It is shown that the heat transfer coefficient does not depend on the thermal properties of chill materials but presumably on the wettability between melt and chill.
  • Measurement of Pore Sizes and the Distribution in Al2O3-SiO2 Bricks by the Mercury Penetration Method

    pp. 297-304

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    The present work aims at quantifying the sizes and the distribution of pores in bricks among a series of various investigations for the characterization and the suitable evaluation of the pore nature. The measurements were carried out for mercury-refractory contact angle by the break-through pressure method and for the pore sizes and the distribution by the mercury porosimetry. The discussion has been based on the hydraulic radius without any models assumed for the pore texture. The results are;
    (1) The contact angles of mercury-alumina and-mullite are 2.54 and 2.44 rad, respectively.
    (2) A good agreement is shown in the water absorption values measured by the mercury porosimetry and the water displacement in vacuum.
    (3) Among the representative radii for the pores in the bricks, the smallest is the mode one, the larger being the area mean, the median, the volume mean in this order, but the area mean radius is not always larger than the mode one. The cumulative volume at the volume mean pore radius is 2.2 times as large as that at the area mean one.
    (4) The composite weibull distribution can be well adapted to the accurate expression of the pore size distribution in the bricks.
  • Differences in Permeations and Surface Areas of Al2O3-SiO2 Bricks by Measuring Methods

    pp. 305-312

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    The present work gives full details of the permeability and the surface area in refractory bricks among a series of studies necessary for the quantitative interpretation on metallurgical phenomena concerned with the pores. The former was investigated by the widely controlled pressure of various fluids and the latter by the Kr adsorption for the same brick specimens as used previously. The discussion has been ranged to the differences and the relations among the results previously obtained in the separate measurements. The main results are;
    (1) The pressure method results in the consistent permeability regardless of the kinds of the fluids.
    (2) Diffusion contributes to the gas flow through bricks due to the pores with the sizes less than 10 times the mean free path.
    (3) The porosimetry results in the surface area which is one and a half time as large as the Kr adsorption method in case of the bricks.
  • Acceleration of Nitrogen Removal with Decarburization by Powdered Oxidizer Blowing under Reduced Pressure

    pp. 313-320

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    A new refining method has been developed for producing ultra low nitrogen steels. Powdered oxidizer was blown onto the molten steel using a special top lance with the argon gas under reduced pressure. As the results, it was found that the nitrogen removal index increased twice as much as that in the oxygen gas blowing and the final nitrogen content could be lowered below 10 ppm easily. The reasons why the satisfactory nitrogen removal was obtaind by using this new method are considered as summarised below.
    (1) The gas-metal interfacial area was increased to twice or five times as large as that the oxygen gas blowing due to the formation of large number of fine CO bubbles during the powdered oxidizer blowing. (2) The oxygen content was maintained at a low level, because the oxidizer efficiency of decarburization reaction was quite high due to the existence of oxidizer particles as nuclei of CO bubble-formation which were penetrated deeply in the molten steel.
  • Quality Improvement of Continuously Cast Billets with In-mold Electro-magnetic Stirrer

    pp. 321-326

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    In-mold electro-magnetic stirrers (M-EMS) have been installed at many plants for improvement of surface and innerr quality of continuously cast strands, but applications of M-EMS to small billet casters are comparatively few. M-EMS's have been installed at the billet continuous caster at Funamachi Works in March 1983. The introduction of M-EMS has contributed greatly on the decrease of surface pinholes and longitudinal corner cracks, and the increase of equiaxed crystal zone of 135mm square billets for bars and wire rods.
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  • Development of Technology for Mold Bath Level Control System of Continuous Caster

    pp. 327-332

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    Studies on fluctuation of mold bath level were carried out to obtain better surface quality of cast slabs.
    (1) The fluctuation occurs due to delay in the movement of slide gate caused by adhesion of solidified steel.
    (2) By the vibration of slide gate, its movement is improved and the fluctuation of bath level is remarkably decreased.
    From these results, the new technology for the automatic bath level control system was developed. A special feature of the system is the addition of a vibratory signal to the control signal of the slide gate.
    The system has been applied to all casters in Wakayama and Kashima Steel Works and as a result, the yield of cast slabs have been remarkably improved
  • Superplastic Behaviour of δ/γ Duplex Stainless Steel

    pp. 333-340

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    A δ-ferrite/γ-austenite duplex stainless steel was recrystallized by rolling at 673 K and subsequent annealing. The superplastic behaviour of alloy sheets prepared by above processing has been investigated in the temperature range from 1123 to 1273 K and over a range of strain rates 4.2 × 10-4 to 2.0 × 10-2s-1.
    The In σ vs. In ε curves were obtained and it was shown that the conditions obtaining the maximum strain-rate sensitivity index m changed from the constant strain rate at temperatures above 1223 K to the constant flow stress below 1223 K, so that the In σ vs. In ε curves were possible to divide into six regions according to the deformation behaviour.
  • Effect of Combined Addition of Nb and Ti on the Mechanical Properties of Extra Low Carbon Steel Sheets

    pp. 341-348

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    Effect of combined addition of Nb and Ti on the mechanical properties of interstitial free (IF) steel sheets was studied comparing with Nb-bearing IF steel (Nb-IF) and Ti-bearing IF steel (Ti-IF).
    With the addition of Ti equivalent to nitrogen content together with Nb, mechanical properties are very much improved compared to Nb-IF, especially when steels are coiled at normal temperature or at the coilend when coiled at high temperature. This is attributed to the formation of large cubic TiN precipitates. On the other hand, fine AIN precipitates is formed in Nb-IF.
    If the content of Ti exceeds the amount equivalent to form TiN, excess Ti forms fine TiC precipitates, and the yield stress tends to increase, while r-value does not decrease so much compared to the above-mentioned case.
    If the Ti is added more than amount equivalent to nitrogen and carbon content, the behavior of mechanical properties tends to become nearly the same as that of Ti-IF. This is attributable to the increase of the size of TiC precipitates.
  • Fatigue Strength of 80 kgf/mm2Grade High Yield Strength Steel with Notch in Synthetic Sea Water at Zinc Potential

    pp. 349-355

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    Effect of zinc potential in sea water on fatigue life of notched specimen was examined using 80 kgf/mm2 grade high yield strength steel. Stress amplitude, stress ratio, and stress concentration factor of the notch were selected as factors affecting the above effect. Testing frequency was 0.5 Hz in sea water. The main results obtained are as follows:
    1) The effect of zinc potential on fatigue life of notched specimen is less beneficial than that of smooth specimen.
    2) The effect of zinc potential on fatigue life of notched specimen depends on stress amplitude, when R = 0.1.
    (a) At a higher stress amplitude, fatigue life is shorter at zinc potential than at free potential.
    (b) At a lower stress amplitude, fatigue life at zinc potential is comparable with that in air.
    (c) At zinc potential, notched specimen fails at a stress amplitude lower than fatigue endurance limit in air.
    3) Effect of zinc potential on fatigue life of notched specimen decreases with increase of stress ratio.
    4) 1), 2), and 3) are explained by;
    (a) decrease of crack initiation cycles at notch tip due to hydrogen evolution at zinc potential and
    (b) increase of crack propagation cycles due to wedge effect at zinc potential in the early crack propagation stage.
  • Fatigue Strength of a High Strength Steel in Various Sea Water Environments

    pp. 356-363

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    The fatigue life was investigated in synthetic sea water at a constant flow rate (condition 1) and in the environment of repetition of the sea water and air for every 1 min (condition 2) using a 80kgf/mm2 grade high strength steel at the frequency of 0.5Hz and 20Hz and at the stress ratio of 0.10. The following results are mainly obtained.
    At the frequency of 0.5Hz and at the stress amplitude of about 35 kgf/mm2 the fatigue life in condition 2 was only a half of that in condition 1. In condition 2, many cracks initiated at the root of the pits with spike-like shape which were about 50-60μm deep, and some of these cracks propagated and linked each other to failure. But in condition 1, many pits with cup-like shape which were less than 10μm deep hardly influenced the crack initiation.
    The difference in fatigue life between condition 1 and condition 2 decreased with decrease of stress amplitude. At the stress amplitude of about 10 kgf/mm2, pits with cup-like shape existed in conditions 1 and 2 which were about 10μm and 50-60μm deep respectively. They hardly influenced the crack initiation.
    The same trend was observed at the frequency of 20Hz as at that of 0.5Hz.
  • Relationship between Creep Strength and γ' Size in a Directionally Solidified Nickel-base Superalloy

    pp. 364-371

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    Correlations of γ' size distributions with creep and creep rupture properties at 900°C under the stress of 30.0kgf/mm2 were investigated using materials three-step heat treated at various solution temperatures on a directionally solidified nickel-base superalloy CM247LC. Size distributions of extracted γ' particles were measured by means of photo-extinction and sedimentation. It became clear that creep rupture lives and minimum creep rates were dependent most preferably on the amount of eutectic γ'-γ' phase, and that, irrespective of solution temperatures and material conditions such as as-cast or heat-treated conditions, the minimum creep rates became higher and the creep rupture lives became lower highly correlatively as the volume fractions of γ' larger than 2 μm in eutectic γ'-γ' regions to the total amount of γ' became greater. According to observations of substructures formed during secondary creep region and secondary cracks formed during creep rupture tests, it was found that eutectic γ-γ' phase did not only contribute inefficiently to creep deformation resistance, but also accelerated crack propagation. This fact is considered to explain possibly the role of eutectic γ-γ' phase in creep properties mentioned above.
  • Effects of Carbide Forming Elements on Hydrogen Attack and Embrittlement in 2 1/4 Cr-1Mo Steel

    pp. 372-379

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    2 1/4Cr-1Mo steel was alloyed with various elements and its resistance to hydrogen attack and hydrogen embrittlement was investigated. The results are as follows:
    1) Hydrogen attack resistance is improved by V addition of more than 0.2 %. Nb, Ti, or Zr addition of less than 0.05 % also has strong beneficial effect. However, W is useless and 0.5 % Ni is harmful.
    2) Hydrogen embrittlement resistance is also improved by V addition of more than 0.2 %. However, Nb, W, and Ni are useless and Ti and Zr are harmful.
    3) Carbides in 2 1/4Cr-1Mo-0.26V steel consist of Cr, Mo, Fe and V, and many fine carbides containing 10-60 % V are formed. These V-rich carbides are thought to be responsible for fining and stabilizing of carbides, which improve resistance to hydrogen embrittlement and attack, respectively.
    4) Nb and Ti are not detected in Cr-Mo-Fe carbides in 0.045%Nb or 0.028%Ti containing steel. This suggests that the beneficial effect on hydrogen attack is due to stabilizing carbon through NbC and TiC formation. However, since solubility of Nb and Ti in austenite is small, fine carbides whose particle number enough to suppress hydrogen embrittlement are not formed.
  • Effects of Local Temperature Rise at a Crack Tip on the Fracture Toughness of 9% Ni Steels

    pp. 380-386

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    The effect of loading rate on fracture toughness of 9% Ni steels with four levels of Charpy absorption energy was studied at various loading rates between impact and static at -196°C. In contrast to the ordinary ferritic steel, the fracture toughness of 9% Ni steel was foud to increase with the loading rate above 20mm/min. The transition of the fracture mode from brittle to ductile took place at the loading rate of 100mm/min, the fracture was completely ductile above this level. The dynamic fracture toughness, Kd, was greater than the static one, Kc. These observations are attributed to the temperature rise at a crack tip during the adiabatic heating at high strain rate, which is emphasized by decreased specific heat and the thermal conductivity at -196°C. The temperature rise during the fracture was measured by a Cu-Constantan thermocouple, and was in good accordance with the previous theoretical prediction. The observed maximum temperature rise was 188°C. The results suggest that not only in 9% Ni steel but in other metals and alloys as well the effect of temperature rise at a crack tip can be an important factor in the dynamic fracture.
  • Fully Automatic Apparatus for Proximate Analysis and Total Sulfur Analysis of Coal and Coke

    pp. 387-393

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    The conventional method of proximate analysis of coal and coke is specified by the JIS method in Japan. This method is based on the loss in weight of the coal and coke sample in air under rigidly controlled conditions of temperature, time and air flow.
    Usually, the above procedure is performed by manual operation throughout the measuring process. However, labor saving of the analysis by automation has been required. We have developed a fully automatic method for proximate analysis and total sulfur analysis of coal and coke by using an electric articulated robot under computer controll.
    Each apparatus, such as the electric furnace, automatic balance, sulfur analyzer, and vibrator, is arranged in the concentric circle position, and the robot is set to the center of the circle.
    Each procedure, such as sampling, weighing and handling is performed by the robot. All processes are controlled by computer (IBM series 1). The results of the measurements are typed out automatically.
    Total sulfur is measured by the combustion and acid-base titration method using a conductivity glass electorode sensor.
    The conditions of laboratory room are improved, as well as we can obtain better precision than with the manual method.
  • 鉄の七不思議

    pp. 398-399

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  • 抄録

    pp. 400-402

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