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

Tetsu-to-Hagané Vol. 50 (1964), No. 14

  • 昭和39年を顧みて

    pp. 2283-2284

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  • Process of Reduction and the Behavior of Carbon-Reducing Agent in the Kiln

    pp. 2285-2293

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    In the previous paper of this series the travel of raw material and the distribution of temperature in a reducing kiln had been discussed.The present study is to investigate the process of reduction and the behavior of carbon-reducing agent in the kiln.
    By using chemical analysis, X-ray diffraction method and observation of microstructure on the specimens which are obtained through sampling holes fixed on the kiln shell, the author finds that the greater part of reduction occurs in the 20pct length from discharge end and the half-reducing reactions proceed as follows:-Magnetite is reduced to wüstite preferentially, ilmenite takes sintering wüstite into ulvöspinel, in the next stage partial reduction to the metallic state of iron from ulvöspinel progresses to some extent under slagging temperature.
    Free wüstite is scarcely recognized throughout the kiln with the exception of 5-9m zone that exists in the early stage of reduction.
    Generally the zone 2-3m from discharge end is approximately reoxidizing on account of the oxidizing atmosphere. This atmosphere is one of the great factors causing dam-ring troubles in a reducing kiln.
    There are two types of consumption of the reducing agent in the burden material; that is, reduction and direct combustion including combustion of carbon monoxide which is a product from reduction.The reactivity of the reducing agent is an important factor for the reduction velocity concerning the consistency of carbon monoxide in the material bed and, at the same time, a factor influencing the consumption in direct combustion.
  • Operation of Foundry Pig Iron with Self-Fluxing Sinter in the Small Blast Furnace

    pp. 2293-2302

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    On the occasion of the 4th blast furnace repairing in September 1960, our company conducted the modernization of the entire installation for pig iron smelting for the purpose of the 100 percent operation of self-fluxing sinter, the chief materials of which come from domestic iron resources.
    This installation consists of a DL type sintering machine with grate area 13.1m2, a blast furnace with hearth diameter 10 ft-6 in and inner volume 129m3, two units of hot stoves with heating surface 5, 000m2, a blower with maximum power 540kW, a Theisen disintegrator with maximum capacity 20, 000Nm3/hr and so on.
    This blast furnace, since started on December 3, 1960, has been smelting the foundry pig iron with the following features for operation:
    1.100 percent operation of self-fluxing sinter.
    2. Perfect control of sizing of burden materials.
    Before being charged into the furnace, the sinter was sized to the mean size of 17mm, 50-5mm: 92 percent upwards, and the cokes to the mean size of 45mm, 70-12mm: 98 percent upwards.
    3. The hot blast of 900°C was used with the adoption of high temperature blast.
    4. By the operation of low basicity: Slag CaO/Si02=1.00±0.05, the decrease of slag volume and the reduction of Si were accelerated.
    Thanks to the methods shown above, the operation of foundry pig iron has shown remarkably excellent records: pig products, 208t/day, productivity, 1.6t/m3; and coke rate 550kg/t despite the fact that no injection of fuel or oxygen was done.
  • On the Primary Inclusions in Steels of Fe-Cr-O System

    pp. 2302-2310

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  • On the Behaviors of Sulfides and Relative Nonmetallic Inclusions Formed in Steel

    pp. 2310-2324

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    The effects of varied elements on the behaviors of sulfides and relative nonmetallic inclusions in a resulfurized steel were morphologically investigated using small scale ingots, whose compositions were based on 0.1%C killed steels with and without Cr and/or Mo.
    At the same time the effects of deoxidizing conditions before solidification were studied, e. g. of various grades of Al killed conditions and vacuum melting process.
    The morphological observation of sulfides etc.was mainly carried out with the microscope; in addition the results were certified by the qualification with the electron probe X-ray micro-analyser and the identification of electrolyzed residues of inclusions by the X-ray diffraction method.
    The obtained results were as follows:
    1. In the case of low carbon steels, the increased S content makes FeS coalesce and float up without forming a network, while the increased C content easily forms an FeS network on the primary grain boundaries.
    2. The increased Mo content up to 2% has a tendency to change the FeS phase to MnS when precipitated in primary crystals, although there exists no increased concentration of Mo in the sulfides.
    3. In the case of Cr-containing steels, the studied morphological aspects of sulfides and selenides were notably affected by the deoxidizing conditions before solidified. Those phenomena can presumably be interpreted from the relations between the natures of deoxidation products and the nucleation of sulfides.
    4. Many kinds of sulfide and selenide inclusions occurring in various conditions were analyzed qualitatively with respect to the effect of Mo and also to the hot plasticity. A relation was observed between the compositions and crystal structures of sulfides and their plasticities also in accord with the Mo contents.
  • Study on the Rimmed Ingot Which Evolved Gas under Reduced Pressure

    pp. 2325-2334

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    Rimmed steels containing 0.03-0.08% C were teemed into slab molds for 8-16t ingot, which had been set in the vacuum tanks without sealing covers. Immediately after teeming, the tanks were sealed and evacuated. As the pressure decreased, the rimming action became extremely stronger, but in the succeeding stage gas evolution became less and less and ceased at 1 mm Hg after 6-8 minutes. And then vacuum was broken and further solidification ensued in the atmosphere showing an appearance close to killed steel ingots.
    In the case of vacuum break at such a high pressure as 10mm Hg, ingot tops became crowned. In order to prevent this phenomenon about 0.3kg/t of aluminum was added at the final stage of degassing.
    Changes of chemical compositions caused by the vacuum treatment were closely examined on the samples taken out from molten steel in the mold immediately after the eeming as well as after the vacuum treatment and later was verified by the check analysis on cold sheets. The equilibrium level of the C-O relation, which was close to atm after teeming shifted following the reaction of carbon monoxide formation, to that of 0.1 to 0.01 atm. Although decrease of carbon and oxygen contents occurs also in the solidification of rimmed steel in the atmosphere, it was very much emphasized by the vacuum treatment. The maximum decrease of carbon was about 0.003%.Further more carbon decreased greatly by injecting oxygen or by adding mill scale into molten steel during vacuum treatment. For example, C-content was decreased 0.067-0012% by injection of oxygen for 10 minutes and in this case a lance pipe with a half inch dia. was consumed 4 meters in length. On the contrary the C-addition to molten steel containing 0.033% after this treatment resulted in a very low carbon steel with oxygen content only 0.08%.The final value of oxygen with no carbon addition was 0.03-0.05%.
    It was noticed that no manganese loss took place during solidification, while the manganese loss was about 0.05% in conventional ingots.
    The structure of 8 t vacuum degassed ingots was considerably similar to that of capped ingots, but superior to the latter, since it showed much less primary holes and thicker solid layers in the rim zone. The segregation pattern was remarkably improved in comparison with the conventional rimmed ingots of the same size and from the same heat. A remarkable improvement of segregation was noticed in 16 t ingots.
    Coinciding to the results of oxygen analysis, (Fe, Mn) O inclusions were greatly reduced both in number and size.Sulphide inclusions were uniformly distributed and very small in size.
    Mechanical properties of cold sheets showed the remarkable merits of vacuum treatment. Drawing quality was very much improved and became considerably uniform in the longitudinal direction of the cold coils.
    To summarize the results shown above, this vacuum degassing process is recommendable for making ingots having cleaner and better quality than conventional capped ingots and a surface as good as rimmed ingots. From the view point of productivity, this process is instrumental for producing very low carbon steel ingots from molten steel higher in C content and consequently for cutting down the smelting time in steel making furnace. This process is also effective to remove a great disadvantage of large remmed steel ingots which tend to show too much segregation.
  • Effect of Lead on the Hot and Cold Working Characteristics of Low Carbon Steels

    pp. 2334-2344

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    Preliminary studies have shown that the hot-workability of a low carbon steel appears not to be deteriorated by the addition of lead if the lead particles included in the steel are finely dispersed and uniformly distributed. Concerning the cold-workability, it has been shown qualitatively that the work hardening rate in the near-surface zone of a steel rod during cold-drawing could be decreased by the addition of lead, although quantitative data on this effect have not been reported.
    In the present investigation, the effect of lead addition on the hotand cold-workabilities of low carbon steels prepared from the same heat has been studied. The test for hot-workability was made with a hot torsion testing machine, while, as industrial scale tests, the hottubing test with a Mannesmann plug mill and the hot-extrusion test by the Ugine Sejournet process were performed.
    Cold-workability was estimated from the work hardening characteristics of the steel under tensile or compressive deformation and the tensile properties after strain ageing were observed.
    The drawing forces for cold plug drawing in the cases of leaded and non-leaded low carbon steels which were hot-finished were compared. Tensile and Charpy impact tests were made on cold-drawn and aged steel tubes and the variation in Charpy transition temperature was observed on the test pieces taken in the longitudinal and transverse directions of the tubes.
    The following results have been obtained:
    (1) The hot torsion test has shown that the twisting number to failure was decreased by the addition of lead, whereas the industrial tests by the Mannesmann and the Ugine Sejournet processes have shown that the hot-workability of low carbon steels was not deteriorated appreciably by the addition of lead.
    (2) The drawing force or the compressive force in the cold-working of steel could be decreased by the addition of lead.
    (3) The work hardening rate during tensile deformation and the hardness after strain ageing were found to be decreased by the addition of lead. These phenomena can be interpreted as caused by the lubrication effect of lead.
    (4) The Charpy transition temperature was raised by cold-drawing, showing a peak at a medium reduction in both the test pieces taken in the longitudinal and transverse directions of the material.
    In the cold-worked steels aged at room temperature or at 250°C, the reduction giving the maximum transition temperature appeared to correspond to the degree of strain at which the locking force on dislocations by interstitial atoms reached the maximum value, while this reduction shifted to a higher reduction by the lubrication effect of lead. In the steels over-aged at 650°C, the largest recrystallized grain size was observed at the reduction giving the highest transition temperature.
  • Controlled Atmospheres in the Sintering Furnace for Sintered Iron Products

    pp. 2345-2350

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    Since iron-graphite compacts are usually sintered in the furnace of atmosphere such as H2 gas or dissociated ammonia gas, the mechanical properties of sintered products are markedly deteriorated through decarburization of the compacts.Authors investigated, in this report, carbon potential of RX gas at sintering temperatures, carburizing and decarburizing reaction and bending strength of the iron, iron-graphite compacts sintered in the RX gas and hydrogen gas.Results of this experiment are as follows.
    1.Carbon potentials of RX gas in sintering furnace can be pre-estimated by extending the theory applicable to the gas carburizing of steel.
    2.When iron compacts are sintered in RX gas, the equilibrium carbon content can not be obtained and considerable differences in carbon content exist between surface and core structure of sintered products.
    3.When iron-graphite compacts are sintered in RX gas, uniform carbon contents in both surface and core structure of sintered parts can be produced by only controlling the dew point of RX gas.The mechanical strength obtained in such a process is superior to those of parts sintered in hydrogen.
  • Recent Studies on Yield Points in Iron and Other Materials

    pp. 2351-2368

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  • On the Impact Tensile Properties of Iron and Steel

    pp. 2369-2386

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  • 抄録

    pp. 2387-2390

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  • 参考文献

    pp. 2391-2393

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  • 鉄鋼ニューズ

    pp. 2396-2397

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