Coherent Laves Phase Finely Precipitated in Heat Resisting High-W and 10% Cr Ferritic Steels
TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN(2002)
摘要
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 10mass% 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 [0 (1) over tilde1](territe)//[110](Laves). In the microstructure aged at 923 K for 7similar to14 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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关键词
ferritic steel,high Cr,heat resisting,Laves,coherent precipitate,martensite
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