Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Coherent Laves Phase Finely Precipitated in Heat Resisting High-W and 10% Cr Ferritic Steels
Yoshinori MURATAKyohei TAKAMIMisaki KAMIYAMasahiko MORINAGARyokichi HASHIZUMEKazuhiro MIKITsukasa AZUMAToru ISHIGURO
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2002 Volume 88 Issue 4 Pages 214-221

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Abstract

In recent advanced high Cr ferritic steels, it is known that the Laves phase precipitates during creep test when the steels contain a relatively high level of Mo+W content. The Laves phase is believed to be granular in shape and to exist in the boundaries of lath, block, packet and prior austenite grains, but a number of fine Laves-phase precipitates are found to exist even inside the martensite lath in the tempered steels containing 10 mass% Cr and 4.6 mass% W. The shape of this Laves phase is plate-like, and the size is below 300 nm. The crystallographic relationship between the fine Laves phase and the matrix phase is as follows; (111)ferrite//(001)Laves and [011]ferrite//[110]Laves. In the microstructure aged at 923 K for 714 Ms, the fine precipitates of the Laves phase disappear inside the martensite lath, and coagulated Laves phase is observed at the lath-, block-, or packet- boundaries. Only the low C steel containing 0.08% C and 3% W shows a few amounts of the fine precipitates of the Laves phase after aging at 923 K for 7.268 Ms. This compositional dependence of the precipitation behaviour can be understood qualitatively with the aid of the System-Free-Energy Concept.

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