Evaluation of Toughness and Creep Properties of Aged Main Valve CrMoV Casting Steel by Using Small Punch Specimens

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Other Title
  • スモールパンチ試験片によるCrMoV鋳鋼製経年主要弁の靱性およびクリープ特性の評価
  • スモールパンチ シケンヘン ニ ヨル CrMoV チュウコウセイケイネン シュヨウベン ノ ジンセイ オヨビ クリープ トクセイ ノ ヒョウカ

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Abstract

It has been required to evaluate material deterioration of plant components with high accuracy, because more than seventy percent of power plants in Japan have been operated for 100, 000 h or more. The small punch (SP) test method can directly determine mechanical properties of components with high accuracy because of a destructive test. Compared with the standard test method using large specimens, it can minimize the damage caused by removing samples from a component because of use of a small specimen. In this study, both the ductile-brittle transition temperature (DBTT) and the creep properties of CrMoV casting steel, which had been used as a main valve in a power plant for 100, 000 h, were estimated by using SP specimens. The conventional SP test results revealed that the SP-DBTT of the aged steel was higher than that of the virgin steel. The actual DBTT determined by Charpy impact tests with V-notched specimens was in relatively good agreement with the calculated one by the SP-DBTT. The results of SP creep test showed that the creep rupture strength of the aged steel was inferior to that of the virgin steel. This degradation of creep properties seemed to be attributed to the microstructural changes and the formation of cavities or micro cracks with the long-term operation. Good correlation was observed between the results of the SP creep test and the standard uniaxial creep test. Consequently, the SP testing method is expected to be an appropriate tool for evaluating material deterioration of plant components in-service.

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 91 (4), 408-414, 2005

    The Iron and Steel Institute of Japan

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