MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Nondestructive Evaluation by Reversible Magnetic Permeability of the Residual Life of Ferritic 9Cr Steel Subjected to Creep-Fatigue Damage
Chungseok Kim
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2018 Volume 59 Issue 2 Pages 316-319

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Abstract

This work presents a nondestructive and magnetic technique for evaluating the residual life of ferritic 9Cr steel using the peak interval of reversible magnetic permeability (PIRMP). The ferritic 9Cr steel was exposed to creep-fatigue damage, and samples were prepared with different damage levels using the interrupt test. The PIRMP decreased continuously with the fraction of creep-fatigue damage. The hardness (Hv) also decreased until failure. The rates of decrease of PIRMP and Hv were 18.2% and 11.8%, respectively, compared with the as-tempered sample. The hardness and PIRMP decreased as a function of the Larson-Miller parameter (LMP) and showed a good linear relationship with the LMP. Mechanical softening was caused by microstructural degradation during creep-fatigue damage. The microstructural features were analyzed and shown to support the variation in hardness and PIRMP. The results are of interest because mechanical softening of structural materials can be evaluated nondestructively by measuring the reversible magnetic permeability. Consequently, the PIRMP offers a useful tool for estimating the residual life of structural materials in a nondestructive and reliable manner.

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© 2017 The Japan Institute of Metals and Materials
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