• Title/Summary/Keyword: 파면양상천이온도

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Estimation of Fracture Toughness Degradation of High Temperature Materials by Nonlinear Acoustic Effects (비선형 음향효과에 의한 고온 재료의 파괴인성 열화도 평가)

  • Jeong, Hyun-Jo;Nahm, Seung-Hoon;Jhang, Kyung-Young;Nam, Young-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.5
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    • pp.424-430
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    • 2000
  • In order to develop an ultrasonic evaluation method for properties degradation of high temperature materials, a number of Cr-Mo-V steel samples were heat-treated and their damage mechanism was examined. Ultrasonic parameters such as velocity, attenuation, and more recently developed nonlinear acoustic parameter were measured. The nonlinear acoustic parameter was found to be most sensitive to material degradation mainly attributed to the precipitation of impurities in grain boundaries. When compared to the electrical resistivity results, the nonlinear parameters showed similar behavior. There existed a relatively good correlation between the nonlinear parameter and the fracture appearance transition temperature (FATT) obtained by Charpy V-notch impact test. Based on the relationship between the FATT and the fracture toughness ($K_{IC}$), correlation between the nonlinear parameter and $K_{IC}$ was established.

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Evaluation of High Temperature Material Degradation for 12Cr Steel by Electrochemical Polarization Method (전기화학적 분극법을 이용한 12Cr강의 고온 재질열화도 평가)

  • Seo Hyon-Uk;Park Kee-Sung;Yoon Kee-Bong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.8 s.251
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    • pp.965-975
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    • 2006
  • High pressure turbine blades are one of the key components in fossil power plants operated at high temperature. The blade is usually made of 12Cr steel and its operating temperature is above $500^{\circ}C$. Long term service at this temperature causes material degradation accompanied by changes in microstructures and mechanical properties such as strength and toughness. Quantitative assessment of reduction of strength and toughness due to high temperature material degradation is required for residual life assessment of the blade components. Nondestructive technique is preferred. So far most of the research of this kind was conducted with low alloy steels such as carbon steel, 1.25Cr0.5Mo steel or 2.25Cr1Mo steel. High alloy steel was not investigated. In this study one of the high Cr steel, 12Cr steel, was selected for high temperature material degradation. Electrochemical polarization method was employed to measure degradation. Strength reduction of the 12Cr steel was represented by hardness and toughness reduction was represented by change of transition temperature, FATT. Empirical relationships between the electrochemical polarization parameter and significance of material degradation were established. These relationship can be used for assessing the strength and toughness on the aged high pressure blade components indirectly by using the electrochemical method.