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

Tetsu-to-Hagané Vol. 101 (2015), No. 9

  • Multiscale Modeling of Ductile Fracture in Continuum Mechanics

    pp. 465-470

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    DOI:10.2355/tetsutohagane.TETSU-2015-022

    A theoretical framework to describe ductile fracture is reviewed from a multiscale perspective based on continuum solid mechanics. Ductile fracture has a hierarchical multiscale structure from a strain localization of a macroscopic structure to debonding of an atomic debinding. In this article, computational methods founded on continuum approximation are addressed, where discretization methods represented by finite element method are featured. These approaches are recognized as promising tools to understand and visualize the deformation and strengthening mechanisms. Here the concepts of description of fracture mechanics are classified into strong discontinuity models and distributed damage models. Also two types of scale-coupling approaches are illustrated to consider the effect of a microscopic heterogeneity on its coarse scale.
  • Effective Desiliconization Method with Swirling Flow of Hot Metal at Blast Furnace Casthouse

    pp. 471-478

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    DOI:10.2355/tetsutohagane.TETSU-2015-041

    Hot metal desiliconization is carried out by adding iron oxide at the tilting runner in the blast furnace casthouse to improve BOF operation. Aiming at effective silicon removal by enhancing mixing of the desiliconizing agent and hot metal, a desiliconization experiment at an actual blast furnace casthouse was carried out with a tilting runner that was specially designed to generate a swirling flow of hot metal.
    1.The amount of removed silicon in hot metal throughout the desiliconization operation was larger under the swirling flow condition of hot metal than under the conventional non-swirling condition.
    2.Hot metal samples taken at the exit of the tilting runner showed that the change in the silicon content of the hot metal in the tilting runner was larger with the swirling condition.
    3.Hot metal samples were also taken from inside the torpedo car, and the desiliconization behavior in a tentative basin part of the torpedo car was evaluated. The calculated silicon content in the basin part was lower with the swirling condition.
    4.A reaction analysis was carried out assuming that the present system is a semi-batch reactor. The reaction rate constant of desiliconization through the swirling part of the tilting runner and the basin part of the torpedo car was 2.2 times higher with the swirling condition. This result qualitatively agrees with the results of previous 5-ton hot metal experiments and reflects the enhanced mixing of the desiliconizing agent and hot metal by the swirling flow in an industrial-scale operation.
  • Analysis of Sticking Breakout with Mechanical Model of Solidifying Shell Growth Considering a Mold Oscillation

    pp. 479-487

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    DOI:10.2355/tetsutohagane.TETSU-2015-016

    In order to prevent a sticking breakout (BO) in continuous casting of steel with high casting speed, a mechanical model of solidifying shell growth, coupled analysis of solidification, stress and strain with considering a shell healing process during negative strip period in one cycle of mold oscillation, has been developed. By employing this model, effects of carbon contents, casting velocity, mold powder viscosity and oscillation conditions on likelihood of the BO occurrence were analyzed. Calculated results obtained are in good agreement with the observations previously reported and BO detection frequency during real operation. By this model, a way of thinking and proper conditions of mold oscillation in high casting speed are elucidated for the prevention of the BO.
  • Effect of the Filling Ratio on the Solidified Structure in Horizontal Centrifugal Casting Process

    pp. 488-493

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    DOI:10.2355/tetsutohagane.TETSU-2015-020

    The effect of free surface on the formation of solidified structure in horizontal centrifugal casting process has been studied. The filling ratio of the transparent organic substance in the glass cell was changed from 70 to 100%. In case of low filling ratio, the columnar and equiaxed zone formed. On the other hand, when the filling ratio exceeded 95%, no equiaxed grain was observed. The equiaxed zone ratio decreased with increasing the filling ratio. Increasing the filling ratio leads to the decreasing the free surface area and this makes the liquid motion stable. This has been confirmed by the model experiment using silicone oil and plastic particles. Therefore, free surface wave considerably influences on the evolution of solidified structure. Especially, free surface wave affects the equiaxed grain formation and their travelling for a long distance.
  • Discussion for Predictions of Gigacycle Fatigue Strength in High-strength Steel

    pp. 494-500

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    DOI:10.2355/tetsutohagane.TETSU-2015-023

    Predictions of gigacycle fatigue strength in high-strength steel were discussed by using reported fatigue test results. The discussed prediction models were Tanaka-Akiniwa model, Murakami’s equation and a new model. The prediction based on the Tanaka-Akiniwa model overestimated the effects of inclusion sizes, resulting in much lower fatigue strength for a large inclusion than actual. The prediction based on the Murakami’s equation provided us good estimations for the effects of the inclusion sizes. However, estimated ODA sizes, which were necessary in the calculation, were imaginary since the estimated fatigue strength did not agree with the fatigue test results. The new model, proposed in this research, was a modification of the Tanaka-Akiniwa model. The new model used a new fatigue crack growth law instead of conventional Paris law. In this new model, coefficient of determination, R2 value, in the fitting of the fatigue test results was maximized to determine a new constant. The prediction based on the new model provided us much better estimations than that based on the Tanaka-Akiniwa model, and the new fatigue crack growth law showed good agreements with the measured crack growth rates for internal small cracks. Validity of the new model was thus confirmed in this research.
  • Development of Single Crystalline Bone Plate with Low Young’s Modulus Using Beta-type Ti-15Mo-5Zr-3Al Alloy

    pp. 501-505

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    DOI:10.2355/tetsutohagane.TETSU-2015-044

    New single crystalline bone plate that has extremely low Young’s modulus was fabricated using an ISO certified biomedical material alloy with a composition of Ti-15Mo-5Zr-3Al in mass %. Single crystals of the Ti-15Mo-5Zr-3Al alloy along [001] direction were succeeded to be grown by using the seed crystal in order to develop the long bone plate along the [001] direction with the lowest Young’s modulus. The ω phase with relatively high Young’s modulus was not confirmed to precipitate in the single crystals at room temperature. Using the oriented single crystals, bone plate with dimensions of 42 × 5 × 1.5 mm3 and 8 holes for screws could be shaped to be along [001], which exhibit the superior low Young’s modulus of ~40 GPa comparable to that along the longitudinal bone axis. The developed single crystalline bone plate has a high potential for a clinical use in the orthopedic field.
  • Bioassay of Components Eluted from Electric Arc Furnace Steel Slag Using Microalgae Chlorella

    pp. 506-514

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    DOI:10.2355/tetsutohagane.TETSU-2014-130

    Some electric arc furnace (EAF) steel slag ultimately ends up in final landfill sites. After developing a method to estimate the impacts of the eluate from the slag, particularly on phytoplankton, this study assessed novel slag applications to aquatic environments. First, metal components were eluted from EAF slags of normal steel or stainless steel with a leaching condition based on JIS K 0058-1. The slag metal components were analyzed using emission spectrochemical analyses. After incubation of Chlorella as phytoplankton with culture media including eluates from the respective slags, the effects of each eluate were investigated using microscopy and flow cytometry. Results demonstrated that concentrations of metal effluents from slags, even for EAF steel slag, which included more hazardous materials than normal slag, were almost all lower than environmental quality standards for effluent and drinking water. Analyses of algal cells treated with each eluate revealed that eluate induced neither lethality nor growth inhibition. Instead of cytotoxicity, the addition of each eluate enhanced algal growth. Infrared spectroscopy and potentiometry using a diaphragm-type electrode to measure aquatic CO2 revealed that metal components from both slags in media produced greater amounts of aquatic CO2 available for photosynthesis, thereby enhancing algal proliferation.
    Taken together, results show that using EAF slag in aquatic environments might be beneficial, not toxic, for photosynthetic organisms. Furthermore, bioassay using flow cytometry can estimate vigorous and aberrant algal growth simultaneously.

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