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

Tetsu-to-Hagané Vol. 106 (2020), No. 1

  • Tribologically Numerical Modeling to Confirm Coefficient of Friction for Cold Rolling Control

    pp. 1-11

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    DOI:10.2355/tetsutohagane.TETSU-2019-073

    The rolling force must be estimated with high accuracy in cold rolling control. For the purpose, the coefficient of friction must be determined with high accuracy. However, if the coefficients of friction determined from conventional methods, the cold rolling control with high accuracy recently becomes difficult. Therefore, it is desirable that a new method for determining the coefficient of friction is developed. In this paper, the tribologically numerical modeling is proposed in order to confirm the coefficient of friction at the interface between roll and workpiece. The coefficient of friction dependences on rolling parameters are calculated by using the model, and from these calculated results it can be confirmed that the coefficient of friction obtained is used efficiently for the cold rolling control.
  • Tracking Technique of Burden Materials for Blast Furnace with Bell-less Top by using RFID

    pp. 12-19

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    DOI:10.2355/tetsutohagane.TETSU-2019-078

    In recent years, in order to reduce CO2 emission and keep productivity in ironmaking process, high gas permeability and high reaction efficiency with maintaining stable operation are required in a blast furnace. To meet these requirements, it is important to control the burden material distribution and material mixed ratio accurately. A new tracking technique of burden materials in charging process by using RFID (Radio Frequency IDentification) tags that are characterized by non-contact ID code recognition has been developed. In this technique, the active RFID tags, built in the durable case imitating coke or ore particles, are putted on the charged materials and detected their ID code at several points on the way of charging route. Their tracking accuracy and detection success rate were evaluated at the actual blast furnaces. As a result, the nut coke imitated tag’s detection ratio on the time series was good agreement with the nut coke mixed ratio measured by sampling at the nut coke mixed charging. By considering the RSSI (Received Signal Strength Indicator), the passing timing of the tag could be estimated accurately within 1.3 s (one sigma) on the belt-conveyor. In the top collection hopper, tags were detected at just passing and its detection success ratio was over 83% of all putted tags. These results indicated that the developed tracking technique of burden materials would be useful for controlling the burden material distribution accurately and improving the blast furnace operation.
  • Vacancy Clustering Behavior in Austenitic Stainless Steels and Nickel-chromium Alloys during Tensile Deformation after Hydrogen Charging

    pp. 20-27

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    DOI:10.2355/tetsutohagane.TETSU-2019-064

    The effects of hydrogen charge on the defect formation behavior in austenitic stainless steels and nickel-chromium alloys during slow strain rate tensile tests (SSRT) were investigated by positron lifetime spectroscopy. Vacancy clustering was significantly promoted by hydrogen charge, although there was no remarkable difference in the dislocation density and mono-vacancy equivalent vacancy density between hydrogen-charged and uncharged samples under the same tensile strains. In various steels and nickel-chromium alloys, vacancy cluster sizes showed a good correlation with breaking elongations of hydrogen-charged samples, implying the vacancy clustering contributes to hydrogen embrittlement by affecting local plasticity.
  • Newly Developed Wear Testing Machine Having Sufficient Reproducibility Useful for Investigating Roller Chains

    pp. 28-38

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    DOI:10.2355/tetsutohagane.TETSU-2019-074

    Roller chains are commonly used for transmission of mechanical power on many kinds industrial machinery. Roller chain makers have done a lot of efforts to improve the wear resistance by using conventional types of wear testing machine. However, such conventional wear testing needs huge amount of time and cost. Therefore, this study focuses on developing a new wear testing machine, which can evaluate the wear amount efficiently without using main chain components such as inner plate, outer plate and roller. The experimental results show that this newly developed wear testing machine may realize the almost same wear rate under stable condition and similar wear status of the conventional chain type testing machine. The newly developed wear testing machine may be useful for improving the wear resistance of roller chains conveniently compared to the conventional chain type testing machine.
  • Application of Kelvin Probe Force Microscopy to Microstructure Evaluation of Steel

    pp. 39-49

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    DOI:10.2355/tetsutohagane.TETSU-2019-058

    Knowing the essence of metallurgical structure is vital for quality assurance and development of steels. Etching has been widely applied as micro-order evaluation of the structure, however not always reliable especially for fine and complex microstructures. The purpose of this study, therefore, is to clarify the application of Kelvin Probe Force Microscopy (KFM) for the evaluation of the fine and complex microstructures.Potential distribution images obtained by KFM were compared with the various images obtained by SEM, EBSD and EPMA for a duplex stainless steel (ASTM A 182 UNS S32750) and a Cu contained low alloy steel (ASTM A707 steel).The KFM was able to clearly identify α, γ, σ and a fresh γ phase in the duplex stainless steel. Moreover, it is concluded that the σ phase itself does not lower corrosion resistance, but on the other hand, the fresh γ phase co-generated with the σ phase can be attributed to the poor corrosion resistance and low toughness of the duplex stainless steel. From the KFM results for the Cu contained low alloy steel, the surface potential distribution obviously depends on surface crystal orientation and chemical compositions, which generally correspond to a work function. The KFM is able to directly show the work function of the surface as the potential distribution. Using the KFM, microstructural features and differences were obviously detected after the two-phase heat treatment for the Cu contained low alloy steel, which corresponds to a better balance of strength and toughness.The present study clarified that the KFM is an effective method to evaluate the metallurgical essence of microstructure especially for the steel having various phases.
  • Environmental Impact Evaluation of Steelmaking Slag Applied to Coastal Area Development

    pp. 50-57

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    DOI:10.2355/tetsutohagane.TETSU-2019-026

    Steelmaking slag came to be used in a marine environment and safety issue of slag material is a matter of concern. We are trying to provide the safety information of the slag material. Experimental facility with mesocosm aquarium tank, which integrated tidal flat area and shallow area, was constructed in order to evaluate the environmental impact. The facility consists of two aquarium tanks, one is the experimental unit using slag materials as dredged soil improver, called CaO-improver, and another is the control unit not using slag materials. Long-term operation over the five years from 2012 to 2017 was carried out to evaluate the long-term safety of slag materials. We observed not only the changes of water quality but also the acute and chronic toxicity assessment using three kinds of aquatic marine organisms such as bioluminescent bacteria, micro algae and copepod for seawater in the aquarium tanks. As a result of the long-term experiment, stabilization of bottom sediment by CaO-improver could be confirmed, but on the other hand, influence of alkali elution from slag was estimated. Furthermore, as a result of three bioassays, it was judged that there was no effect of acute toxicity and chronic toxicity on organisms caused by slag material within the range examined.

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