Abstract
Creep-fatigue and oxidation properties of Zr-free and Zr-containing HK40 and HP centrifugal heat-resisting alloys were studied. The mechanism of improving these properties by Zr addition was discussed through microstructural examination of materials. The following results were obtained;(1) A small amount of Zr addition markedly impoves the low-cycle-fatigue life under creep conditions, creep rupture strength and ductility, and oxidation resistance of HK40 and HP.(2) The improvement of creep-fatigue properties is thought to be brought about by the following two effects;(i) Zirconium gives an excellent resistance to the localized oxidation of eutectic carbides and/or grain-boundaries, which can be fatigue crack initiation sites.(ii) A number of small Zr-carbides (ZrC) are precipitated homogeneously in grains at elevated temperatures. These carbides suppress the formation of sub-boundaries and the precipitation of coarse carbides (M23C6) on sub-boundaries, which can be fatigue crack propagation paths.
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