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

Tetsu-to-Hagané Vol. 98 (2012), No. 8

  • Effects of Physical Properties of a Droplet on its Falling Behavior on an Inclined Hydrophobic Flat Plate

    pp. 389-396

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    DOI:10.2355/tetsutohagane.98.389

    Investigation on the dynamic behavior of a molten metal droplet moving on a hydrophobic surface is of essential importance for the efficiency enhancement of the current ironmaking and steelmaking processes. Many water model experiments have been carried out on the behavior of a droplet moving down on an inclined hydrophobic flat plate. Information on the effects of the physical properties of the droplet however is very limited. In this study, water droplets containing fine CaCO3 powder of different weight percents are used in addition to a water droplet and a mercury droplet to change the density, kinematic viscosity, and surface tension. The dynamic behavior of the droplet is observed with a high-speed camera. An empirical equation is proposed for the acceleration of the droplet as a function of the Molton number.
  • Development of FCG (Flow Control Gate) Dynamic Control Technique at Mixed Charging of Massive Coke into Ore Layer

    pp. 397-404

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    DOI:10.2355/tetsutohagane.98.397

    A method of improving control of the radial mixed coke ratio distribution under high coke mixed charging, which is called FCG (Flow Control Gate) dynamic control method, was studied with the aim of stable operation with high productivity and low RAR at Chiba No. 6 blast furnace. For this purpose, scale model experiments and mathematical burden distribution model calculations were performed. The effects of FCG dynamic control with ore and coke simultaneous discharging from the respective top bunkers on the mixed coke ratio distribution were examined and applied to Chiba No. 6 blast furnace. After application of FCG dynamic control, improvements of gas utilization efficiency: +0.2%, gas permeability at cohesive zone (the part of lower shaft): −14.7% and coke ratio: −4.2kg/t (with constant RAR) were confirmed. Since June 2007, high productivity operation with low RAR has been conducted at Chiba No. 6 blast furnace.
  • Formation Mechanisms of Several Kinds of Segregation on Continuous Casting of Bloom

    pp. 405-414

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    DOI:10.2355/tetsutohagane.98.405

    Formation mechanisms of several kinds of segregation (V segregation, Centerline segregation, negative segregation near center part of bloom section) on continuous casting of bloom are investigated by some examinations on formation behavior of each segregation and distribution of solute element on cross section of bloom and using some analyses. As the results of these examinations and analyses, these formation mechanisms are clarified as follows. V segregation is gradually formed by flow of interdendritic liquid caused by negative gradient of pressure resulted from shrinkage flow existing on center side of cross section of bloom. The shrinkage flow on solidification proceeding to crater end forms the centerline segregation and the negative segregation near center of cross section of bloom, to promote mass transfer of solute in mushy zone, in vertical direction to solidification interface toward to center of cross section.
  • Tensile Test Method with Image Analysis to Obtain True Stress - True Strain Curve Up to Fracture

    pp. 415-424

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    DOI:10.2355/tetsutohagane.98.415

    A new tensile test method to obtain a true stress - true strain curve was developed, in which a CCD camera and an image analysis device were equipped to enable the in-situ measuring of the change in shape of test specimen until the very end of the fracture. A smooth round bar tensile test specimen was adopted. The dynamic change in the necking geometry was observed continuously with a CCD camera and the measured data was simultaneously processed by an image analyzer. Tensile tests were carried out using SS400 steel and 5.0%Mn steel. The data of the radius of cross sections perpendicular to the specimen axis around the necking portion, the radius of curvature on the longitudinal section of necking surface, and the load applied to the specimen were obtained continuously until the specimen ruptures. The change in the minimum radius of the neck and the necking curvature were calculated from the data obtained, and they were confirmed to be accurate. According to the Bridgman’s model, true stress - true strain curve after necking can be obtained from the minimum neck radius, the neck curvature and the load. The data was analyzed based on the Bridgman’s model. True stress - true strain curves of SS400 and 5.0%Mn steels were determined by this method. True stress - true strain behavior after necking was thus elucidated. This newly developed test method is confirmed to be applicable for the accurate measurements of true stress - true strain curves until up to fracture of specimen.
  • Effect of Stress on Variant Selection of Lath Martensite in Low-carbon Steel

    pp. 425-433

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    DOI:10.2355/tetsutohagane.98.425

    The effect of stress on variant selection of lath martensite in a low-carbon steel (Fe-0.18%C-0.89%Mn-2.88%Ni-1.51%Cr-0.40%Mo) was investigated by EBSP analysis. The steel was continuously cooled from fully austenitic temperature to room temperature under uniaxial compressive stress applied during the martensitic transformation. It was demonstrated that, only in blocks larger than the average block size, some of the variants were preferentially selected under the applied stress while maintaining the Kurdjumov-Sachs (K-S) orientation relationship with the prior austenite. Otherwise, no clear variant selection was found. The external work done during the martensitic transformation evaluated from the transformation strain and the applied stress showed that the variants with greater external work were more likely to be selected. However, both the shift of martensite start temperature and the selected variants indicate that the transformation strain effective for the variant selection of lath martensite in the low-carbon steel was only the invariant line strain, unlike in nickel steels where the additional lattice invariant shear has been included in the literature.
  • Precipitation Behavior of V and/or Cu Bearing Middle Carbon Steels

    pp. 434-441

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    DOI:10.2355/tetsutohagane.98.434

    In this study, the precipitation behavior of middle carbon steels with single and multiple additions of 0.3mass%V and 2mass%Cu has been investigated. The precipitation treatment was carried out isothermally at 600°C.
    In the 0.3mass%V bearing steel, precipitates were observed in rows, indicating the occurrence of the interphase precipitation. On the other hand, precipitates observed in the 2mass%Cu bearing steel were randomly dispersed. In the V and Cu bearing steel, Cu precipitates were not randomly dispersed and mainly observed attached with VCN which were precipitated in rows. In the paper, the different precipitation behavior of the three steels is discussed in detail and is explained from a viewpoint of the thermodynamics and kinetics using a metallurgical model.
  • Mean Stress Effect on Fatigue Strength in Gray Cast Iron and Its Mechanism

    pp. 442-449

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    DOI:10.2355/tetsutohagane.98.442

    The effect of mean stress on the fatigue strength of gray cast iron was examined and its mechanism was investigated. Fatigue endurance limits were experimentally obtained by round bar fatigue tests under various stress ratios. The critical stress amplitude for the fatigue endurance limit decreased with an increase of mean stress, but its dependence on mean stress was not the linear relation that the modified Goodman relation suggests. A fractography technique was applied to the fractured specimen in different stress ratios. The fracture appearance in the stress ratio range −1 ≤ R < 0.6 suggested that the fatigue crack initiated from large size graphite and propagated to the Pearlite matrix, whereas that in the stress ratio range R ≥ 0.6 showed a static fracture feature of dimple pattern. The fatigue endurance limit in the stress ratio range −1≤ R < 0.6 was analyzed by fracture mechanics. The relation between mean stress and stress amplitude was calculated from the threshold value of effective stress intensity factor, ΔKeff,th with an assumption of an initial crack size similar to the maximum graphite length of the material. The estimated relationship, which represents the mean stress effect on the stress amplitude of fatigue endurance limit, quantitatively agreed well with the experimental results, in spite of there being no references to the fatigue endurance properties of the material.
  • Estimation of Steel Use in Buildings by Night Time Light Image and GIS

    pp. 450-456

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    DOI:10.2355/tetsutohagane.98.450

    Steel is the most widely used material among all metals. As the concern about effective use of the in-use steel stock as secondary resource grows, numerous studies analyzing the flow and stock of steel have been conducted. Though top-down and bottom-up approaches have been employed in material flow analysis, the applicability of these approaches is largely restricted by the data availability. To overcome this problem, we have proposed a method for estimating in-use steel stock based on satellite images. Our previous studies had shown effective regression of steel stock in buildings and nighttime lights on country and sub-national level. However, the relationship has not been examined in micro level, i.e. building stocks and pixels. Therefore, in this study, geographic information system (GIS) was used to estimate the in-use steel stock for buildings in Tokyo, Japan. The volume of buildings in 145 areas with 1 km square in Tokyo was calculated with GIS. Then, the correlation was investigated between the building volume, in-use building steel stock and the radiance of nighttime light. As the result, building volume and in-use building steel stock were found to be highly correlated with the radiance of nighttime light.
  • Erratum: Formation of Fine Macrostructure in Ferritic Stainless Steel [Tetsu-to-Hagane Vol.98 (2012) No.7 p.351-357]

    pp. 457-457

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    DOI:10.2355/tetsutohagane.98.457

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