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

Tetsu-to-Hagané Vol. 57 (1971), No. 2

  • 人と技術開発

    pp. 199-200

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  • Study on the Burn-Out Mechanism of Tuyere

    pp. 201-212

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    To protect tuyeres from failures which were mainly caused by burn-out, their thermal states and burn-out were studied. The temperature and heat flux distributions in tuyeres and cinder notches were measured in operation, and burn-out tests were also made on water-cooled Cu-plates on which molten steel was poured.
    The results obtained are as follows;
    1. In normal operation, measured temperatures of a tuyere are about 200 in the upper portion of its nose; and about 100° in the lower one and its inner wall. The heat flux is 40-400×101 kcal/m2 hr in the tuyere nose.
    2. In normal slag-tapping operation, temperatures of a cinder notch are ranged from 140 to 190° in its nose and ranged from 110 to 150 in its inner wall. The heat flux in its nose indicates the maximum value, about 200×104 kcal/m2. hr.
    3. From the experiment of burn-out of Cu-plates, burn-out heat flux (Bo) is derived as a function of the temperature and velocity of the cooling water. In the case of inlet water at 27° and 1 m/sec, qBo of Cu-plate with 20 to 30 mm in thickness is about 750×104 kcal/m2·Ehr.
    4. The burn-out heat flux of actual tuyeres is estimated above 400-700×104 kcal/m2·hr, which is obtained only during contact with a great amount of molten metal. Hence, it is assumed that burn-out of a tuyere in operation occurs only when it contacts with a great amount of pig iron.
  • Some Considerations on the Rate of Absorption of Nitrogen in Liquid Iron

    pp. 213-221

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    The kinetics of the absorption of nitrogen in liquid iron were studied.
    The overall process of nitrogen absorption is devided into such two processes that nitrogen molecules are activated by collision with another nitrogen molecules, and then activated nitrogen molecules dissolve into liquid iron.
    Introducing the LINDEMANN'S mechanism, it could be explained that the rate of nitrogen absorption in liquid iron containing surface active elements is controlled by activation process of nitrogen molecules. However, in the range of lower concentration of surface active elements, it is controlled by dissolution process of those activated nitrogen molecules.
    The process of nitrogen removal under reduced pressure could be similarly understood by application of this LINDEMANN'S mechanism.
  • On the Solid State Reactions between Mn-Fe Alloy and Synthetic Sulfide Inclusion

    pp. 222-236

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    In order to clarify the reactions between sulfide inclusion and matrix in rimmed steels at high temperatures, a synthetic sulfide slag was embeded into various Mn-Fe alloys and the solid state reactions between them were studied at 1 100°-1450°. Results obtained here are as follows. 1) Sulfide were formed in the alloys by sulfur transfer from slag to surrounding matrix. Manganese concentration in matrix decreased rapidly. The region of precipitation of sulfide particles widened with increases of time and temperature and with the decrease of initial manganese concentration in matrix. 2) Repeating solution and precipitation, sulfide precipitates coagulated to larger particles. As a result, there appeared a zone without precipitates in the neighborhood of the slag-metal interface. 3) The shapes and localities of precipitates were affected by oxygen concentration in alloy. When the oxygen concentration was very low, precipitates appeared at the grain boundaries. On the contrary, when the concentration was high, precipitates appeared at random and were accompanied with some oxides. 4) Silicon in alloy prevented a little the sulfur transfer and the precipitation of sulfide.
  • Studies on the Reductions of Solute Segregation in the Steel Ingots from the Viewpoint of Solidification Rates

    pp. 237-262

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    In order to reduce the solute segregation in steel ingots casted into iron molds, casting methods have been investigated specially from a viewpoint of solidification rate of molten steel.
    Solidification rate of molten steel has been calculated by SARJANT'S in the case of big end down rectangular molds. The calculated times for complete solidification have been in relatively good agreements with the observed ones obtained by bar-test method. Accordingly this method has been applied to calculate the influence of mold thickness or mold radiator on the time for complete solidification of steel ingots. The obtained results have shown that these effects have been practically negligibly small. Electrical method has been used to measure the time for air-gap formation between mold and ingot initiated immediately the teem-end, and a calculative method for estimating the time for gap formation has been established.
    Some experiments in practical scale have been done in order to investigate the scraping method which were reported to be beneficial in reducing the segregation in steel ingots. It has been concluded, however, that this method can not be effective for segregation without eliminating the horizontal solidification from the mold wall.
    Finally a new method has been devised, in which some coolant such as air or water is introduced directly into the air gap and accelerates the enhanced cooling of steel ingots effectively. The experimental results have shown that the solute segregation is remarkably reduced by this method.
    x

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  • Macro Structure and Segregation of Continuously Cast Carbon Steel Billet

    pp. 263-286

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    The macro structure and the segregation of continuously cast carbon steel billets with 80 to 250mm square and 260×370mm in section were investigated. The results were summarized as follows.
    1. The length of columnar crystal and the thickness of central segregated zone are increased, and the central porosity and segregation become worse, with increase of superheated casting temperature.
    2. The absolute thickness of central segregated zone is increased with increase of the section of square billet, but its relative value to billet thickness is decreased. The type of V segregation is changed from single V line to multi V line, in the case of high superheat temperature.
    3. The type of V segregation is changed from V line to V zone and the central segregation disappear, when the billet shape is changed to rectangular.
    4. The maximum positive segregation ratios of Mn and C are 1.3 and 1.8 respectively, which are obtained by the analysis of specimen with 3 mm in dia and 3 mm in depth taken from the central segregated zone high carbon billet with 160 mm square in section.
    5. The length of columnar crystal and the width of central segregated zone are increased in the order 0.3%C, 0.1%C and 0.6%C steel under the same condition of super heated casting temperature.
    6. The mechanism of formation of equiaxed dendrite and V segregation are discussed.
    x

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  • Reaction between Alloy and Synthetic Oxide at High Temperatures

    pp. 287-297

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    In order to obtain informations on the change of oxide inclusions in steels by annealing at high temperatures, synthetic oxide slags were embeded into various alloys. After annealing at high temperature, the size and shape of precipitates were observed microscopically and changes of both compositions were analysed by EPMA. Results obtained here are as follows:(1) Oxide particles precipitated in a layer around the embeded oxide. The thickness of the precipitation layer broadened with increases of time, temperature and FeO content in oxide, and shortened with decrease of initial concentration of alloying element in the alloy.(2) The precipitates had various shapes including sphere, and the size increased with time and temperature. FeO content in precipitates decreased as the precipitate departed from the oxide/alloy interface, and concentration of alloying element in the alloy near the precipitates became far lower than the initial concentration.(3) FeO content in the embeded oxide decreased. Besides, it was observed that silicon transfered from the oxide into alloy.
  • The Effect of Inclusions on Fatigue Properties of Steels with Various Matrixes

    pp. 298-334

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    Alternate bending fatigue tests were carried out using specimens containing FeO-type inclusions, containing Mn-silicate type inclusions and containing substantially no inclusions respectively. The effect of inclusions on endurance limit was discussed. Some specimens were carburized and heat-treated in order to intensify the effect of inclusions on fatigue properties. Main results obtained are as follows:
    1) Inclusions in low carbon steels do not exert any effect on endurance limit.
    2) Influence of inclusions in carburized steels (0.25% C) on the endurance limit increases with the decrease of tempering temperature. The trend is remarkable in specimens containing Mn-silicate type inclusions, when the axis is transverse to the rolling direction. Inclusions in steels as carburized, however, do not influence the endurance limit.
    3) Inclusions have little effect on ultimate tensile strength, but have a considerable one on reduction of area.
    4) On the assumption that inclusion does not adhere to matrix, rate of reduction of endurance limit by inclusions is expressed by W=i (A-n), where i is a coefficient depending on size, amount and shape of inclusions, n is the work hardening coefficient defined by σ=kεn and A is a constant. In tis experiment, A was nearly 0.16. When n is larger than about 0.16, it is concluded that inclusions do not affect endurance limit. The above equation can not be applied for pre-strained specimens, in which case the work softening controlls the fatigue process.
    5) Heterogeneous microstructure has worse influences on elongation and reduction of area than on endurance limit.
    6) Effect of inclusions on crack propagation could be estimated from disorder of striation around inclusions.
  • A Model Experiment on Relationship between Fatigue Properties of Steel and Size, Shape, and Distribution of Inclusions

    pp. 335-354

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    The effect of inclusions on fatigue properties was mainly discussed from the viewpoint of size, shape and distribution (amount) of inclusions. Specimens were prepared by using powder-metallurgical method in order to control conditions of inclusions in steel. Angular and spherical Al2O
    3 powders of 10μ, 30μ, 45μand 100μ in size were used as inclusions. Some specimens were carburized and heat-treated to intensify the effect of Al2O
    3 on fatigue. Main results obtained are as follows:
    1) In the case of non-carburized specimens.
    (a) Endurance limit increases with an increase of Al2O
    3 content. The trend is remarkable, when the size of Al2O
    3 is large for a constant mean particle spacing.
    (b) UTS and lower yield stress increase also with an increase of Al2O
    3 content. But the rates of increase with Al2O
    3 are small compared with those of endurance limit.
    (c) Elongation and reduction of area decrease with an increase of Al2O
    3 content independently of the size.
    2) In the case of carburized and heat-treated specimens.
    (a) Endurance limit decreases with an increase of Al2O
    3 content. The trend is remarkable when the work hardening coefficient of specimen is small.
    (b) Th effect of angular Al2O
    3 on endurance limit is larger than that of spherical Al2O
    3 when their size is constant.
    (c) The effect of large Al2O
    3 on endurance limit is larger than that of small Al2O
    3 when their shapes and distribution are constant.
    (d) The rate of decrease of endurance limit by Al2O
    3 decreases with an increase of Al2O
    3 content.
    (e) Elongation and reduction of area decreases with an increase of Al2O
    3 content.
  • Study on Properties of Chromized Austenitic Alloys

    pp. 355-366

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    An extensive study has been made on corrosion characteristics and mechanical properties of S590 alloy chromized by powder method. Chromized S590 alloy showed slight gradual weight gain and was not suffered from accelerated corrosion when it was exposed in combustion gas of buncker C residual fuel at a velocity of 40-50 m/sec and at a temperature of 720-790°C for 600 hr, while the same alloy without chromized layer indicated a remarkable weight loss according to linear rate law.
    Chromizing was also proved to be very effective by full immersion test and contact test using synthetic fuel ash. There were some changes in corrosion resistance of chromized S590 in synthetic fuel ash depending on chromizing method by Cr-Al2O3 powder mixture and that by Cr-Fe-Al2O3 mixture due to differences of surface chromium concentration of the layer.
    When solution treated and aged S590 alloy was chromized at 1050°C for 10 hr, some deterioration of mechanical properties were observed. This deterioration resulted from resolutionof fine carbides and coagulation of coarse carbides.
    Among various heat treatments prior and posterior to chromizing, the following process was proved to be most favourable for mechanical properties of chromized S590, that is, solution treatment at 1180°C→chromizing at 1050°C for 10 hr, →aging at 760°C for 16 hr.
  • Improvement of High Temperature Strength of 2 1/4 Cr-1 Mo Heat Resistant Steel

    pp. 367-385

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    In order to develop a low alloy heat resistant steel which has a higher creep-rupture strength than that of 2 1/4 Cr-I Mo heat resistant steel, the effects of simultaneous addition of Ta, V, Ti, Co, Nb, and B on creep-rupture strength and oxidation resistance of 21/4 Cr-1 Mo steel were investigated.
    The creep-rupture strength of the steel at 600°C was improved by simultaneous addition of these elements, which was mainly due to precipitation hardening by V4C3 and NbC. The oxidation resistance of the steel at 600°-700°C was slightly improved by simultaneous addition of Co, V, Nb, and Ta, but the addition of B was not effective for the improvement of the oxidation resistance.
    As the result, the steel with nominal composition of 0.15% C, 2% Cr, 1% Mo, 0.4% V, 2% Co, 0.12% Ti, 0.02% Nb, with or without 0.03% B was selected as the best. 105 hr creep-rupture strength at 600°C obtained from the master rupture curve of this steel was 11.3kg/mm2, which was about 2.6 times higher than that of 2 1/4 Cr-1 Mo steel. It was concluded that this favourable creep-rupture strength for long time is mainly due to the excellent structural stability of the steel.
  • Effect of Precipitates on Recrystallization Behaviors of Aluminum-Killed Steel Sheets

    pp. 386-410

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    The recrystallization behaviors of two aluminum-killed steels were investigated in isothermal annealing and continuous heating, starting with either as hot-rolled (as taken from productional hot strip coils) or as cold-rolled (ca. 70%).
    Careful electron microscopy (carbon extraction replica), run along with the measurement of solute nitrogen by internal friction method, revealed that, even when no evidence of A1N precipitation is apparent, there is definitely some precipitation of AIN of almost sub-electron microscopic sizes. The electron diffraction pattern of those minute A1N precipitates did not conform to that of hexagonal A1N, but fit very well with that of a hypothetical cubic A1N of NaCl type structure with (a)=4.047Å.
    It was seen that the recrystallized textures were closely related to the state of the cubic A1N precipitation;(1) when the recrystallization began after the precipitation of cubic AIN had progressed to certain extent, in the unrecrystallized region, strong texture with {554}‹225› and {111}‹011› as its major components resulted, (2) when the precipitation of cubic A1N proceeded concurrently with recrystallization, very strong texture with {111}‹011› as its major component resulted, and (3) when the recrystallization had been completed before the precipitation of cubic A1N, the texture was weak, being similar to that of rimmed steel sheets.
  • On Preliminary Desulphurization of Molten Pig Iron

    pp. 411-429

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  • Prospects of Instrumental Analysis for Iron and Steel Making

    pp. 430-437

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  • 抄録

    pp. 438-449

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