Microstructural evolution in a strip-cast Ni-base superalloy
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Microstructure and mechanical properties of the strip-cast Ni-base superalloy(Hastelloy-X) alloy have been compared with those of a conventionally ingot-cast alloy. As-cast strip shows a fine columnar dendritic structure as a result of a relatively high cooling rate of 102 -104 K/sec during the process. The alloying elements, such as Cr and Fe, are homogeneously distributed in the γ matrix of the as-cast strip. Whereas, Mo is segregated at the center part of the as-cast strip. Mo distribution, however, becomes homogeneous after cold rolling and subsequent heat treatment at 1175°C. Two types of carbide, a Mo-rich M6C type and a Cr-rich M23C6 type, are present in the γ matrix of the as-cast and rolled strips. Rolling and subsequent heat treatment of the strip-cast alloy results in a fine grain structure compared to the ingot-cast alloy. The γ matrix grains in stripcast and ingot-cast alloy are approximately 14 μm and 34 μm in diameter respectively. Superior tensile properties in the strip-cast alloy is due to the fine microstructural evolution during the process.
KeywordsCold Rolling Carbide Particle Secondary Phase Particle Rolled Sheet Subsequent Heat Treatment
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