The microstructural features of INCOLOY alloy 617 in the solution annealed condition and after longterm creep tests at 700 and 800 C were characterized and correlated with hardness and creep strength. Major precipitates included (Cr,Mo,Fe)23C6 carbides and the d-Ni3Mo phase. M6C and MC carbides were also detected within the austenitic grains. However, minor precipitates particularly c¢-Ni3(Al,Ti) was found to play an important role. At different exposure temperatures, the microstructural features of the Ni–22Cr–12Co–9Mo alloy changed compared with the as-received condition. The presence of discontinuously precipitated (Cr,Mo,Fe)23C6 carbides and their coarsening until the formation of an intergranular film morphology could be responsible both for a reduction in rupture strength and for enhanced intergranular embrittlement. The fraction and morphology of the c¢-phase, precipitated during exposure to high temperature, also changed after 700 or 800 C exposure. At the latter test temperature, a lower volume fraction of coarsened and more cubic c¢ precipitates were observed. These microstructural modifications, together with the presence of the d-phase, detected only in specimens exposed to 700 C, were clearly responsible for the substantially good creep response observed at 700 C, compared with that found at 800 C.

Creep behaviour of INCOLOY alloy 617

GARIBOLDI, ELISABETTA;RIPAMONTI, DARIO
2008-01-01

Abstract

The microstructural features of INCOLOY alloy 617 in the solution annealed condition and after longterm creep tests at 700 and 800 C were characterized and correlated with hardness and creep strength. Major precipitates included (Cr,Mo,Fe)23C6 carbides and the d-Ni3Mo phase. M6C and MC carbides were also detected within the austenitic grains. However, minor precipitates particularly c¢-Ni3(Al,Ti) was found to play an important role. At different exposure temperatures, the microstructural features of the Ni–22Cr–12Co–9Mo alloy changed compared with the as-received condition. The presence of discontinuously precipitated (Cr,Mo,Fe)23C6 carbides and their coarsening until the formation of an intergranular film morphology could be responsible both for a reduction in rupture strength and for enhanced intergranular embrittlement. The fraction and morphology of the c¢-phase, precipitated during exposure to high temperature, also changed after 700 or 800 C exposure. At the latter test temperature, a lower volume fraction of coarsened and more cubic c¢ precipitates were observed. These microstructural modifications, together with the presence of the d-phase, detected only in specimens exposed to 700 C, were clearly responsible for the substantially good creep response observed at 700 C, compared with that found at 800 C.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/528175
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