高温長時間クリープ特性の推定での信頼性向上
丸山 公一
pp. 767-777
抄録
The present critical review aims at evaluating long-term creep properties from short-term tests with enough reliability. Two examples cited in the present review are extrapolation of creep rupture lives of short-term creep tests to longer term by means of the Larson-Miller equation and evaluation of a rupture life of an on-going creep test from its minimum creep rate with the aid of a Monkman-Grant relation. Short-term creep tests as short as 1 h are carried out at higher temperatures, and their results are extrapolated toward lower temperature and longer term as long as 1 Mh. A temperature range of the tests can be 200 K. This means that the total variation of effective creep duration is 9 orders of magnitude in terms of diffusion of atoms. In the extrapolation, temperature dependence of rupture life, in other words, a Larson-Miller constant C is assumed not to change from the high temperatures to the low temperature. The Monkman-Grant relation determined by short-term creep tests at higher temperatures and higher stresses is applied directly to the long-term on-going creep test. However, microstructures, creep deformation mechanisms and creep fracture mechanisms of a material cannot be kept unchanged over the wide time range. The difference between the assumption and the reality can result in a large difference between the creep rupture life evaluated and the actual creep rupture life. It will be discussed what should be done for improving reliability of the evaluation.
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鉄と鋼 Vol.105(2019), No.8
鉄と鋼 Vol.105(2019), No.8
鉄と鋼 Vol.105(2019), No.8