Study of Aging-Induced Degradation of Fracture Resistance of Alloy 617 Toward High-Temperature Applications
- PDF / 2,428,589 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 21 Downloads / 169 Views
DUCTION
TOWARD meeting the demands for doubling the electric energy generation in coming decades[1] with low greenhouse gas (CO2) emission in fossil-fired power plants, operating conditions with very high steam temperature and pressure have been envisaged worldwide. However, toward achieving this goal, selection of proper materials for the piping system ensuring resistance to creep deformation, corrosion resistance, and long-term microstructural stability is a major technological challenge for researchers. In this endeavor, where the conventional high-temperature materials like ferritic–martensitic steels (P91, P92) fall short of these requirements,[2,3] the use of Ni-based superalloys[4–7] is showing a promising potential owing to their better creep rupture life and corrosion resistance in the operating conditions.[8] Among Ni-based superalloys, Alloy 617 is one of the forerunners as the candidate
ADITYA NARAYAN SINGH, A. MOITRA, PRAGNA BHASKAR, G. SASIKALA, ARUP DASGUPTA, and A.K. BHADURI are with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam, Tamil Nadu, 603 102, India. Contact e-mail: [email protected] Manuscript submitted September 29, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
piping material for high-temperature applications and are likely to be used in a temperature regime from 973 K to 1033 K (700 C to 760 C) under high pressures of 35 MPa.[9–12] Alloy 617 is known to draw its high-temperature (>973 K/700 C) strength both from the solid solution (ensured by Co and Mo) strengthening[13] and from the precipitation strengthening originating from the ordered c¢ phase (Ni3 (Ti, Al)) and M23C6 precipitates. The oxidation resistance[14] is assured by Cr and Al. In addition to these properties, this alloy also shows good fabricability.[15] The microstructural constituents like grain size and precipitate variants and their evolution during the service condition influence the mechanical properties of alloys significantly, especially during the service conditions. For the Alloy 617, in spite of having desirable properties in the as-received condition, the effect of microstructural degradation on the mechanical properties after long-term exposure to service conditions has always been a matter of great concern to the designers. The literature in this direction has reported several efforts correlating the microstructural changes with the creep, fatigue, or creep crack growth during aging[16–18] at high-temperatures, often pointing to severe deterioration compared with the as-received material. However, the literature data on the
aging-induced microstructural changes on the fracture properties of this alloy is scanty. Guo et al.[19] have reported a significant drop in fracture resistance even after a short aging treatment for 300 hours at 1033 K (760 C). A similar observation has been reported by Nanstad et al.,[20] where the 36 pct degradation of fracture energy was observed just after 200 hours of aging at 1023 K (750 C). Although the results have been attribute
Data Loading...
