Small Punch Creep Life Prediction from Steady-State Deflection Rate in High-Chromium Ferritic Heat-Resistant Steels
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CREEP rupture life in conventional uniaxial creep tests can be predicted using minimum creep rate from the Monkman–Grant model,[1] which defines relationship between the minimum creep rate and time to rupture. The small punch (SP) creep test which utilizes small specimens can be employed as an effective tool for evaluating creep rupture properties of materials.[2–8] The test method can determine creep properties with a high accuracy because of a kind of destructive test. Since the test needs miniaturized specimen (diameter: 3 to 10 mm and thickness: 0.25 to 0.5 mm),[9] it is advantageous over conventional full scale creep test. A great amount of effort has been made by a number of researchers to deepen the understanding of both, the SP creep test results and its correlation to conventional uniaxial creep test results, and it is still evolving. The applicability of Monkman–Grant relationship in SP creep test has been
NAVEENA is with the Division of Mechanical Engineering, Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan. Contact e-mail: [email protected] SHIN-ICHI KOMAZAKI is with the Research Field in Engineering, Science and Engineering Area, Research and Education Assembly, Kagoshima University, Kagoshima 890-0065, Japan. Manuscript submitted August 3, 2017. Article published online January 23, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
investigated by a number of authors.[10–14] It was found that the minimum deflection rate can be well correlated to the time to rupture. In SP creep test, the minimum deflection rate appears in the latter half of creep life, just before the onset of acceleration creep, unlike in uniaxial creep tests. As a result, to determine minimum deflection rate, one has to carry out the SP creep test until almost the rupture of specimen. In this regard, instead of minimum deflection rate, if the steady-state deflection rate that would appear prior to minimum deflection rate is available and can be used for predicting creep rupture life then it is more advantageous. This would permit one to forego the necessity of running the creep test until rupture of the specimen. In SP creep test, the relationship between steady-state deflection rate and time to rupture has not been analyzed so far. Therefore, the present study was undertaken to investigate steady-state creep deformation as well as rupture behavior and their interrelationship in high-chromium ferritic heat-resistant steels and to analyze the possibility of predicting creep rupture life using steady-state deflection rate. We investigated this in different high-chromium ferritic heat-resistant steels which vary by its chemical compositions, heat-treatment conditions and microstructures with a view to examine their influence on steady-state deflection rate–time to rupture correlation and prediction of creep rupture life from this correlation.
VOLUME 50A, APRIL 2019—1655
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EXPERIMENTAL PROCEDURE
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The high-chromium ferritic heat-resistant steels considered for the present investigat
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