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Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

REVIEW ARTICLE

Fujio Abe

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TOPICAL REVIEW

It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of creep strength and for improving long-term creep strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher creep strength at 650 °C than existing high-strength steels used for thick section boiler components.


PACS

62.20.Hg Creep

81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

81.40.Lm Deformation, plasticity, and creep

84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Subjects

Electronics and devices

Condensed matter: structural, mechanical & thermal

Dates

Issue 1 (January–March 2008)

Received 26 September 2007, accepted for publication 15 November 2007

Published 13 March 2008



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