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

Tetsu-to-Hagané Vol. 86 (2000), No. 6

  • Magnetic Separation of Inclusions in Molten Metal Using a High Magnetic Field

    pp. 363-369

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    A new method for separating inclusions from molten metal using a high magnetic field has been proposed. The principle of this method based on a magnetization force has been confirmed in experiments with Al-Si-Mn-Fe, Bi-Mn and Al-Si alloys, in which precipitated particles of intermetallic compounds and silicon imitating inclusions in molten metal were separated.
    In order to measure magnetic susceptibility, the Gouy's method has been modified by using a super conducting magnet to work in a high temperature up to 1200°C. The theoretical expression of the magnetization force which is indispensable to evaluate the magnetic susceptibility has been derived. By use of the expression, the magnetic susceptibility of the intermetallic compounds used in the experiment of magnetic separation was measured over the range of liquidous to solidous temperatures.
  • Composition Analysis of Calcium Ferrite in Iron Ore Sinters by EPMA Scanning Method

    pp. 370-374

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    To investigate the association of calcium ferrites in iron are sinters with aenigmatites, composition analysis of sinters is carried out by applying EPMA scanning method. Most of the calcium ferrite in sinters has been classified to aenigmatites. The stability domain of SFCA is bound by the three lines of 4CaO·3SiO2-CaO·3(Al, Fe)2O3, CaO·SiO2-CaO·6(Al, Fe)2O3 and SiO2CaO·3(Al, Fe)2O3 in the pseudo (CaO+MgO)-SiO2-(Fe2O3 +Al2O3) system.
  • Synthesis of Iron Carbide from Hematite Pellets with H2-CH4 Gas Mixture

    pp. 375-380

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    The purpose of this investigation is to examine the effect of properties (porosity, specific surface area, particle size distribution and impurities) of hematite pellets on the synthesis of Fe3C pellets. The experiments were carried out by using six kinds of reagent hematite pellets with H2-CH4 (70:30) gas mixture at 750°C. The synthesis of Fe3C pellets were confirmed all kinds of hematite pellets except two kinds of ones. One of the most suitable pellets for the synthesis of Fe3C was converted to high purity Fe3C (on XRD level) within about 110min and the phase was stable at least for 3h, even though excessive carbon deposited at the surface of pellets. Excessive carbon deposition could be stopped with lowering CH4 concentration to an equilibrium gas composition for Fe3C generation reaction.
    Two kinds of pellets contained relatively low impurities did not form Fe3C. Such high purity pellets tended to shrink due to sintering during reduction stage, and the structure of reduced iron had much less micro pores. This phenomenon might cause decrease of adsorption sites for CH4 molecule and therefore the enough carbon deposition necessary for Fe3C formation hardly could occur.
    The correlation between other properties (porosity, particle size distribution) and Fe3C formation was not confirmed in detail.
  • Mechanism of Uneven Thermal Distribution Formation during Water Cooling at Low Temperature for a Moving Plate

    pp. 381-387

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    In order to investigate the basic mechanism of uneven thermal distribution formation at low temperature during water cooling for a moving plate, an experimental study with full cone spray cooling or flat spray cooling was carried out.
    The results obtained under certain conditions are summarized as follows.
    (1) The quench point was at a temperature range between 230°C and 240°C during full cone spray cooling, and it was almost constant for a stationary plate and a moving plate.
    (2) The cooling curve varied with starting temperature of cooling, velocity of the plate and water flux during flat spray cooling. Three types of thermal distribution were formed in the following order, as starting temperature of cooling decreased.
    Type I: Uneven thermal distribution was formed in the case where the temperature of the whole surface after cooling is higher than the saturation temperature of water (100°C).
    Type II: Uneven thermal distribution was formed in the case where the surface was cooled partially to the saturation temperature of water.
    Type III: Uniform thermal distribution was formed in the case where the temperature of the whole surface was cooled to the saturation temperature of water.
    (3) Both quenching during full cone spray cooling and forming of type II·III during flat spray cooling could be explained by a boiling mechanism (i.e. film boiling, transition boiling and nucleate boiling) in a temperature range of 180°C to 200°C.
  • Blast Erosion Properties of Erosion-resistant Thermally Sprayed Coating

    pp. 388-395

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    Blast erosion properties of Plasma sprayed coating, Arc sprayed coatingand PTA layer were assessed by using four kinds of erosion-resistant spraying particles. The results obtained are follows.
    (1) Blast erosion property of Plasma sprayed coating is worse than that of SS400 base metal.
    (2) Ripple pattern is formed on the eroded area of the surfaces of SS400 base metal and PTA layer. On the other hand, thin sheets are piled up on the eroded area of the surfaces of Plasma and Arc sprayed coating.
    (3) The wear mechanism of erosion of PTA layer is thought to be scratch erosion by shear stress of erodent. On the other hand, the mechanism of erosion of Plasma sprayed coating, in which porosities and microcracks are, is thought to be the separation and omission of thin sheets.
  • Relationship between Surface Structure of Silicon Containing Steel and Adhesion of Hot Dip Galvanized Coating

    pp. 396-401

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    The surface of the annealed steel and the exfoliated interface of the coating for the hot dip galvanized Si containing steel sheets was characterized by using SEM (Scanning Electron Microscope), AES (Auger Electron Spectroscopy) and TEM (Transmission Electron Microscopy). The adhesion of the coatings have depended on the Si content of the steel. It have been found that MnSiO3 particles are formed at the surface of the annealed steels having high Si content and that two types of grain having different distribution of the oxide exist in the steels. Large oxide particles have been formed in one type of grain and small particles are formed in the other type of grain. The different type of Fe-Zn alloy are formed on two types of grains. It have been observed that the oxide particles exist at the interface of exfoliated coatings after the adhesion test for the steels with high Si content. The distribution of the oxide particles observed at the bottom of the exfoliated coating is quite similar to that of the surface oxide of the annealed steel. From these results, the exfoliation of the coating has initiated at the oxide particles of the steel surface that has been not reduced during the hot dip galvanizing.
  • Effect of Microstructure on Low-cycle Fatigue Property of Structural Steels under Large Plastic Deformation

    pp. 402-408

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    Low-cycle fatigue behavior of the structural steels under large plastic strain was investigated using notched round specimens. Crack growth rates show good correlation with the value of effective J-integral range, ΔJeff. Crack growth rates are strongly affected by microstructure of the steels. It was shown that steels with higher pearlite volume fraction have lower crack growth rate. Many voids were observed around crack tip in the steel with higher pearlite volume fraction, which shows that the void growth and coalescence mechanism is dominant in this type of steels and crack growth were suppressed by branching and curving of the crack. On the other hand, in the steel with lower pearlite volume fraction, voids were hardly formed near crack tip region and crack propagates by plastic blunting and re-shaping mechanism, keeping the crack shape strait. Fatigue failure life were affected by MnS inclusion content. Large amount of void nucleation and growth were observed in the inner region of the specimen of the steel with large MnS content during cyclic loading, and final failure was occurred with a very short crack extension. It can be said that final toughness is improved by reducing MnS inclusion content and pearlite volume fraction, which can prevent void nucleation and growth in the inner region during cyclic loading.
  • Ductile Crack Propagation Characteristics and Mechanism of Structural Steel under High Strain Rate

    pp. 409-416

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    In the present study, it was carried out to clarify the characteristics and the mechanism of ductile crack propagation of HT490 structural steel, with special emphasis on the influence of strain rate. At first, bend test was performed in various displacement rate, and subsequently deformation microstructure was observed by using optical microscope and scanning electron microscope.
    It was found that higher strain rate increased the resistance to ductile crack propagation extremely. The mechanism that higher strain rate increase the resistance to ductile crack propagation is considered as follows: Higher strain rate suppresses multiple slip and cross slip. Therefore, the number of slip systems acting on primary voids is limited and then equiaxed growth of primary voids is suppressed. And also, the cross point of multiple slips, which could be the site of secondary voids, is decreased and the coalescense of primary voids may be suppressed. They lead to decrease in the area mainly composed of equiaxed dimple, and to increase in the area mainly composed of elongated dimple and the area of shear lip. Consequently plastic deformation accompanying the formation of ductile fracture surface is increased, and then the resistance of ductile crack propagation become higher.
  • Wear and Shelling Behavior in Pearlitic and Bainitic Rail Steels with Various Tensile Strengths

    pp. 417-424

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    Resistance to wear and surface damaging (shelling) in pearlitic and bainitic steel rails with various tensile strengths ranging from 850 to 1400 MPa were examined by wear and rotating contact fatigue tests. The pearlitic steels showed better wear resistance than the bainitic steels for all the test conditions tested, although the amount of wear varied according to the strength range and contact pressure used in the wear tests. The wear behavior of the pearlitic steels was roughly described by a Holm's-type equation (W=kP/H; where W: amount of wear, P: contact pressure, H: hardness and k: constant), while that of the bainitic steels showed complex dependencies on the strength and contact pressure. The bainitic steels, however, showed superior damage resistance to the pearlitic steels for all the test conditions tested: at a fixed tensile strength of 850 MPa, significant shelling was observed in the pearlitic steel after 200 h testing, while no damage was detected in the bainitic steel even after 500 h. The resistance to shelling of the pearlitic steels was improved by strengthening, but the opposite trend was obtained in the bainitic steels. These results were analyzed taking work hardening on the sample surface into consideration. Additionally, the formation behavior of the "white phase", which was the martensite phase formed on the rail-head surface by friction between rails and wheels, was compared in pearlitic and bainitic steels and discussed metallurgically.
  • A Macro Model for Steel Usage Pattern in Japan Using the Population Balance Model

    pp. 425-430

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    The macro model for evaluating the amount of CO2 emission by virgin production, disposal and recycling of steels in Japanese society is proposed. The steels are classified into two groups for machinery and constructions, and it is assumed that steels are discharged from the society in accordance with each lifetime distribution, which is approximated by the gamma distribution. The amount of recycling steel and the stock are calculated using the population balance model with the input data of the statistics and estimated values for basic steel production, domestic consumption ratio and consumption ratio for constructions. The validity of this model is verified by the comparison with the calculated results and statistics of stock and steel production by electric furnaces. The copper concentration in recycling steel and the amount of total CO2 emission are also calculated. The effect of recycling ratio on the total amount of CO2 emission is analyzed under the assumption that recycled steel is diluted with virgin steel not so as to exceed the allowable copper concentration. The results show that recycling ratio is upper-bounded at 21st century because of the necessary dilution and that the total amount of CO2 emission is not much reduced by increase of recycling ratio.

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