Change in Temperature Dependence of Creep Rupture Life of High Cr Ferritic Steel

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  • Maruyama Kouichi
    Department of materials science, Graduate School of Engineering, Tohoku University
  • Nakamura Junya
    Department of materials science, Graduate School of Engineering, Tohoku University
  • Yoshimi Kyosuke
    Department of materials science, Graduate School of Engineering, Tohoku University

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Other Title
  • 高クロムフェライト鋼のクリープ破断時間における温度依存性の変化
  • コウクロムフェライトコウ ノ クリープハダンジカン ニ オケル オンド イソンセイ ノ ヘンカ

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Abstract

Conventional time-temperature-parameter (TTP) methods often overestimate long-term creep rupture life of high Cr ferritic steels. The cause of the overestimation is examined paying attention to temperature and stress dependence of creep rupture life of Gr.91, 92 and 122 steels. In stress-rupture data of all the three steels there are four regions with different values of stress exponent n for rupture life. Activation energies Q for rupture life in the regions take at least three different values. The values of n and Q decrease in a longer-term region. The decrease in Q value is the cause of the overestimation of long-term rupture life predicted by the conventional TTP methods unable to deal with the change in Q value. Therefore, before applying a TTP analysis to stress-rupture data, the data should be divided into several data sets so that Q value is unique in each divided data set. When this multi-region analysis is adopted, all the data points of the steels can be described with higher accuracy, and their long-term rupture life can be evaluated more correctly.

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 100 (3), 414-420, 2014

    The Iron and Steel Institute of Japan

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