Kinetics of the Formation of Intermetallic Phases in HP-Type Heat-Resistant Alloys at Long-Term High-Temperature Exposur
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TRODUCTION
HEAT-RESISTANT casting alloys of the HP series (Fe-25Cr-35Ni-0.45C wt pct, plus micro additions of Nb, Ti, Si, W, Mn, and rare metals) are widely used by the petrochemical industry to make high-temperature components in pyrolysis and reforming systems.[1–4] This equipment operates at temperatures of 1173 K to 1273 K (900 C to 1000 C) with local temperature occasionally rising up to 1423 K (1150 C) for a short duration. Bulky casting blocks with wall thickness 50 mm produced of HP alloys by chill and centrifugal molding. The initial as-cast microstructure of these alloys is sharply defined, by an optical metallographic, heterogeneous dendritic morphology and consists of three main phases. These phases are: the matrix c-solid solution with a chemical composition close to an average of the alloy; the eutectic, which consists of the c-phase and carbides; and matrix carbides.[5–10] Such structure is formed as a result of a carbon segregation because of its slight solubility in c-phase (
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