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

Tetsu-to-Hagané Vol. 73 (1987), No. 7

  • Benefactors of Steelmaking Technology in Japan

    pp. 751-760

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  • Speed Effects in Deep Drawing

    pp. 761-769

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    [in Japanese]
  • Looking for New Intermetallic Compounds with New Unique Properties

    pp. 770-777

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  • Technology for the Production of High Quality Large Ring Forgings

    pp. 778-785

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  • Cermets for Friction Materials

    pp. 786-795

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  • Development of Coal Gasification-Iron Ore Reduction Process by Fluidized Bed

    pp. 796-803

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    This study was made to investigate a process in which the gasification of coal and the reduction of iron ore took place simultaneously in a reactor. Fluidized bed was selected for the type of reactor from preliminary study on reduction time at 800°C.
    The result obtained from the tests using hydrogen gas, mixed gas and recirculating gas with 100 mm inner diameter reactor are as follows.
    1) Metallization more than 90% can be achieved at reaction temperature above 920°C with mean resident time above 10 minutes.
    2) Metallization is affected with the ratio of half the number of hydrogen atomes as a form of hydrogen, moisture and hydro-carbon contained in gasses, ore and reductant supplied to the reactor and the total number of iron atomes contained in ore, since in this process there are always solid carbons such as char in the reactor. The molar ratio of the hydrogen/Iron is to be preferably more than 4.
    3) Coking coal which tend to cause sintering is also usable provided that more active fluidization or rapid gasification is maintained.
  • Pore Forming Process on Iron Ore Sinter and Its Model

    pp. 804-811

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    On the controlling factors for sinter qualities, sinter porosity plays an important role together with the mineral composition. The present work was carried out to study on sinter pore and its forming mechanism by pot tests and to develop the sinter porosity evaluation model.
    Pores in sinter were formed as the pores in raw mix bed were changed and redistributed by the forming sinter melt. predicted porosity in sinter was described by the melting ratio of raw materials and the fluid index of sinter melt. Sinter porosity was measured on the small open pores below 0.5 mm in diameter and the all closed pores by JIS method.
    The calculated porosities by the model were in good agreement with the observed ones.
  • Reduction Rate of Molten Iron Oxide by the Solid Carbon or the Carbon in Molten Iron

    pp. 812-819

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    The reduction rates of molten iron oxide by the solid carbon or the carbon in molten iron were measured, in order to collect basic data on the smelting reduction process which consists of blowing powder iron ore and powder coal into molten iron bath with oxygen gas for a partial combustion. Molten iron oxide in a steel or an alumina crucible was reduced by a rotating carbon rod. The carbon in molten iron in an alumina crucible was reacted with molten iron oxide which was melted in a steel container beforehand. The reduction rates were calculated from the amount of CO gas evolved. The following results were obtained :
    (1) The reduction rates of molten iron oxide by the solid carbon were 0.21-0.82×10-4mol-FeO/cm2·s at 1 420-1 620°C, and the activation energy of the reaction were 75 and 31 kcal/mol for a steel and alumina crucibles, respectively.
    (2) The reduction rates of molten iron oxide by the carbon in molten iron were 1.1-3.3×10-4mol-FeO/cm2·s at 1 420-1 620°C, and the activation energy of the reaction was 44 kcal/mol.
    (3) It was concluded that the reaction rate between the solid iron oxide and the carbon in molten iron was the highest among reactions between the solid or the molten iron oxide and the solid carbon, the carbon in molten iron, CO, or H2 gas.
  • Kinetic Study on the Smelting Reduction of Bottom-injected Chromite Ore Powder by Dissolved Carbon in Iron Melt

    pp. 820-827

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    Pulverized chromite ore was injected into 20 kg of molten iron from the bottom, so that the ore should be reduced by the dissolved carbon. The affects of temperature, ore injection rate, flow rate of carrier gas and powder size on the chromium yield and reduction rate were examined.
    The chromium yield increased linearly with temperature, decreased with the ore injection rate and decreased linearly with the mean diameter of powder. The gas flow rate did not affect the yield. The highest yield of about 100% was obtained with the ore injection rate of less than 20 g/min at 1 680°C. From the behavior of silicon during the process, it is concluded that the oxygen transport in the melt should be the rate controlling step. The reduction process could be divided into transitory and permanent reactions. The fraction of transitory reaction was from 60 to 75% at 1 500 and 1 600°C, and more than 80% at 1 680°C. The rate of transitory reaction increased proportionally to the 2/3 power of ore injection rate, and decreased proportionally to the inverse square root of the mean diameter of powder. The gas flow rate did not affect the rate. The apparent activation energy was 46.0 kcal/mol. From these, it is suggested that several particles of powder penetrate together into the melt, accompanying some amount of gas, at the nozzle exit.
  • Effect of Applying Electromagnetic Force on Falling Behaviour of Molten Metal Film

    pp. 828-835

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    In order to obtain a uniform and stable molten metal film, the shape control function induced by high frequency magnetic field is utilized.
    Firstly, the falling behaviour of liquid film shaped by a slit nozzle was observed in a water-model experiment by use of a high speed VTR. The falling liquid is classified into two regions. Namely, one is denoted as the film flow region appearing in the middle part of the falling liquid and the other as the channel flow region appearing in both sides of the film flow region. The width of the film flow region decreased continuously with increase in the falling distance. A mathematical model predicting the falling behaviour of the liquid film is developed on the basis of hydrodynamics and is verified by the water-model experiment.
    Then, the effect of magnetic field on the falling molten-metal film is studied by the mathematical model taking into account the magnetic pressure induced by magnetic field.
  • The Development of a Mathematical Model of Endpoint Control System for Top and Bottom Blowing Process in BOF

    pp. 836-843

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    For the endpoint control of top and bottom blowing process in BOF, a simplified mathematical model suitable for online application has been developed on the following procedure.
    (1) The basic equations of oxygen consumption rate and temperature increase rate have been developed, which have the comprehensive characteristics in both low carbon range and high carbon range.
    (2) Based on these basic equations, the fundamental curves of oxygen consumption and temperature increase, which show the progress of blowing, have been determined by analysis of actual operational data. The fundamental curve of dephosphorization also has been determined in the same way.
    (3) The authors have developed a control model for endpoint carbon content and endpoint temperature of metal by using these fundamental curves.
    At No. 2 BOF shop in Kashima Steel Works, the model is being used for the automatic blowing and contributes to the reduction of reblow ratio and furnace refractories.
  • Indirect Measurement of Behaviors of Process Variables in Converter Process Based on the Exhaust Gas Information

    pp. 844-851

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    For the improvement of the endpoint control of BOF, a new mathematical model has been developed, which combines dynamic equations of material and heat balance with the exhaust gas information based on mass-spectrometer.
    The outline of model calculation is as follows;
    (1) By use of the amount of oxygen and submaterials which come into BOF and the composition and flow rate of the exhaust gas which goes out of BOF, the amount of oxygen consumed in the surface of cavity and oxygen consumed by decarburization can be determined.
    (2) By including the above calculated value of the amount of oxygen in the model based on reaction theory, the transition of composition and temperature of steel bath can be estimated.
    At No. 1 BOF shop in Wakayama Steel Works, the model is being used for the guidance of the operation and contributes to the reduction of reblow ratio.
  • Inclusion Float-out Behavior in Continuous Casting Tundish Bath

    pp. 852-859

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    The Floating behavior of inclusions in the tundish bath was studied in connection with the fluid flow state of molten steel. A mathematical model which predicts the inclusion removal efficiency has been developed. It was postulated in the model that the tundish bath consists of three regions : a mixing flow region, a plug flow region and a stagnant region. In the mixing flow region, predominated by inertia force or turbulent viscous force, inclusions are transferred by various sized vortices. In the plug flow region, predominated by viscous force, inclusions are transferred approximately according to Stokes's law. The stagnant region is not involved in inclusion transfer owing to long-stagnation.
    The validity of the model was comfirmed by the results of cold model experiments and actual operations. It was found by the above model that the use of a longer and deeper tundish bath was effective for promoting the floating removal of inclusions owing to the increased plug flow region. In addition, placing dams in the tundish retarded the removal efficiency, since the dam increased the mixing flow region.
  • Promotion of Inclusion Float-out in Continuous Casting Tundish Bath by Gas Blowing

    pp. 860-867

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    The gas blowing method using a perforated plate, was studied to solve the problem of decrease of inclusion removal efficiency in a tundish bath on the high casting speed. The floating behavior of inclusions in the tundish bath during gas blowing was studied in connection with the fluid flow state of molten steel. A mathematical model which predicts the inclusion removal efficiency has been developed. It was postulated in the model that the tundish bath consists of three regions : a mixing flow region, a circulating flow region and a stagnant region. In the mixing flow region, inclusions are transferred by various sized vortices. In the circulating region produced by gas blowing, inclusions are transferred mainly by upward flow. The stagnant region is not involved in inclusion transfer.
    The validity of the model was comfirmed by the results of cold model experiments and actual operations. It was found by the above model that the uniform bubbling flow occurred in the low flow rate of gas was effective for promoting the floating removal of inclusions and the faster the casting velocity, the stronger this effect became.
  • Mass Spectrometric Determination of the Miscibility Gap in the Liquid Fe-Sn System and the Activities of This System at 1 550°C and 1 600°C

    pp. 868-875

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    The miscibility gap in the liquid Fe-Sn system has been determined by a Knudsen-cell mass spectrometric combination. The limits of miscibility gap could be determined in situ by this technique. The determination was performed for the composition range 10.1 to 89.2 at%Sn and for the temperature range 1 200 to 1 600°C. The consolute point has been found to be located at about 1 495°C, and the limits of the miscibility gap have been determined at various temperaturs. The consolute point obtained in this study is lower than the literature values.
    The activities of Fe and Sn at 1 550°C and 1 600°C were determined from the ion current ratios for various alloy compositions by the use of the modified Gibbs-Duhem equation. Though the activity curves exhibit large positive deviation from ideal behavior, the obtained activity curves change smoothly with the composition, which show no existance of the miscibility gap at these temperature.
  • Hot Cracking of Low Alloy Steels in Simulated Continuous Casting-direct Rolling Process

    pp. 876-883

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    Surface cracking during direct rolling of continuously cast low alloy steel slabs has been investigated by means of hot tensile tests simulating the above process. The hot ductility of directly cooled specimens is not reduced by high strain rate deformation corresponding to that in rolling. While, in the specimens predeformed at temperatures ranging from γ/α duplex phase to lower temperature γ region at slow strain rate corresponding to that in bending and/or straightening processes of CC slabs, ductile intergranular fracture of austenite is easily induced by the subsequent deformation even at high strain rate, resulting in poor ductility. This ductility loss can be explained in terms of dynamic precipitation of carbonitrides such as AlN and/or NbC within the matrix as well as on the grain boundaries during the prior slow strain rate deformation. Although the embrittlement mechanism is essentially the same as in CC slabs, the ductility is also influenced by the final deformation conditions because of the morphological change of carbonitride precipitates in the process.
  • The Effect of Chemical Compositions of Steel on Nb Compound and Its Chemistry Formed in Controlled Rolled HSLA Steel Plate

    pp. 884-891

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    The effects of C, N and Nb contents and processing variables on the chemical compositions of Nb compounds formed in controlled rolled HSLA steel plates were systematically investigated. Identification of Nb compounds and determination of X and Y values in NbCxNy were performed by chemical analysis and X-ray diffraction on the precipitates extracted by electro-chemical method. Nb compound formed in commercial HSLA steels was δ phase of NbCx or NbCxNy. NbCx with X value of 0.84 to 0.86 was formed in the steels with the very low N content or with the addition of small amount of Ti. X + Y value in NbCxNy was almost constant in around 0.83 to 0.86, while X or Y value was widely varied depending on N content in steel.
    The δ' phase of NbN was formed exceptionally in the high N-Nb steel containing an extreamly low carbon content less than 0.003%. The reduction of slab reheating temperature in controlled rolling or post heat treatment increased the amount of AlN precipitates, resulting in the decrease of N content in NbCxNy. The map describing formation of various Nb compounds and their chemical compositions was drawn based on C/Nb and N*/Nb mole ratio in steel, where N* was free nitrogen not combined with Al or Ti.
  • Effect of Test Conditions on the Corrosion of Painted Zn-Alloy-Electroplated Steel Sheets

    pp. 892-898

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    Cyclic Corrosion Test (CCT) and Salt Spray Test (SST) for the paint adhesion at cross script were compared using painted Zn and Zn-Fe electroplated steel sheets with various contents of Fe. The changes of paint adhesion with the composition of Zn-Fe electrodeposits largely depended on the testing procedures, CCT and SST. When SST was employed, paint adhesion at cross script was improved with an increase of Fe content of Zn-Fe electrodeposits. On the contrary, in CCT paint adhesion was decreased with an increase of Fe content. In a range of Fe content of 70-90%, paint adhesion was worst. The paint adhesion of Zn-Fe electroplated steel sheets containing a small amount of Fe was superior to pure Zn plated steel sheet. Appearances of cross section of blisters were different in CCT and SST. In CCT, a lot of corrosion products accumulated under blister of specimen showing poor paint adhesion. On the contrary, in SST corrosion products did not appear. Corrosion potentials of blister and script were different in those corrosion tests. pH of the solution in blister in SST showed 10-12 and that of script showed 4-6. In the case of CCT, pH of the solution in blister was 4-6 and that of script showed 10-12. The corrosion behavior in CCT was similar with that of filiform corrosion. It was suggested that paint deadhesion in CCT was caused by lifting up the paint by corrosion products.
  • Superplastic Warm-die and Pack Forging of Powder-consolidated Nickel-base Superalloy Mod. IN-100

    pp. 899-906

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    The superplastic behaviour (total elongation and strain-rate sensitivity index m) of a powder-consolidated nickel-base superalloy Mod. IN-100 preformed by extrusion under various conditions has been measured at 1 050°C. The results showed that a sample piece extruded with 72% at 1 100°C and annealed at 1 070°C for 1h had the maximum in m at strain rate about 2.0×10-2 s-1.
    Subsequently, the sample piece preformed under the condition as mentioned above, packed in 5mm-thick carbon steel (S535C) and heated at 1 100°C was superplastically forged at strain rate about 1.8×10-2 s-1using Inconel 713C dies previously heated at about 600°C. As a result, the sample piece was sound after forged.
    Furthermore, the results showed that the heat treatment for grain coarsening after superplastic forging should be performed at the temperature range of 1 200-1 275°C.

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