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PHYSICAL METALLURGY OF ALLOYS 718, 725, 725HS, 925 FOR SERVICE IN AGGRESSIVE CORROSIVE ENVIRONMENTS
ABSTRACT
Processing conditions were designed to produce alloys 718 (UNS N07718), 725 / 725HS (UNS N07725), and 925 (UNS N09925) with essentially clean grain boundaries, partial coverage of grain boundaries by the precipitates, and full coverage of grain boundaries by the precipitates. Grain boundary precipitates were found to degrade room temperature impact strength. Partial coverage of grain boundaries by second phase particles did not adversely affect the properties in slow strain rate (SSR) tests conducted in the oil patch environments. However, the materials having grain boundaries fully covered with second phase particles had inferior properties in SSR testing.
Key Words: UNS N07718, UNS N07725, UNS N09925, slow strain rate, oil patch, microstructure, time-temperature-transformation diagram, grain boundary precipitates, processing.
