Alumina-forming austenitic (AFA) heat-resistant steels have been reported as a promising new class of steels in recent years with potential applications in advanced ultra-supercritical power plants. It is well known that L12-ordered γ’ phase is the most important precipitate for high-temperature strengthening in Ni-based superalloys and it can be stabilized by increasing the Ni content in heat-resistant steels. In the current work, the evolution of L12-ordered precipitates were compared in the Cu-bearing AFA alloys with 20, 27 and 35 wt.% Ni. After slow tensile tests at 700°C (∼2 × 10−5 s−1), L12-ordered precipitates occurred in all the alloys. Alloy AFA27 displayed the most densely distributed L12-particles in the matrix, whose ultimate tensile strength was also the highest. However, the L12-ordered precipitates were only observed in alloy AFA27 after the slow tensile test at 750°C due to the thermodynamic and kinetic reasons. Flow curves of slow tensile tests indicated different precipitation behaviors at 700°C and 750°C. Chemical composition analysis and thermodynamic calculation revealed that the occurrence of L12-ordered Ni-Cu-Al phase depends on temperature, Ni content and the atomic ratio of Ni/Al. This opens up new opportunities to promote the formation of L12-ordered phase in Fe-based austenitic heat-resistant steels with low Ni content and benefits high-temperature strengthening.
- International Gas Turbine Institute
Introduction of L12-Ordered Precipitation to Alumina-Forming Austenitic Heat-Resistant Steels With Low Ni Content
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Zhao, B, Dong, X, Sun, F, & Zhang, L. "Introduction of L12-Ordered Precipitation to Alumina-Forming Austenitic Heat-Resistant Steels With Low Ni Content." Proceedings of the ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy. Charlotte, North Carolina, USA. June 26–30, 2017. V006T24A006. ASME. https://doi.org/10.1115/GT2017-63621
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