Creep and oxidation behavior of modified CF8C-plus with W, Cu, Ni, and Cr

Journal Article · Mon Feb 01 00:00:00 EST 2016 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-016-3348-3· OSTI ID:1246771

Unocic, Kinga A. ^[1]; Dryepondt, Sebastien N. ^[1]; Yamamoto, Yukinori ^[1]; Maziasz, Philip J. ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Here, the microstructures of modified CF8C-Plus (Fe-19Cr-12Ni-0.4W-3.8Mn-0.2Mo-0.6Nb-0.5Si-0.9C) with W and Cu (CF8CPWCu) and CF8CPWCu enhanced with 21Cr + 15Ni or 22Cr + 17.5Ni were characterized in the as-cast condition and after creep testing. When imaged at lower magnifications, the as-cast microstructure was similar among all three alloys as they all contained a Nb-rich interdendritic phase and Mn-based inclusions. Transmission electron microscopy (TEM) analysis showed the presence of nanoscale Cu-rich nanoprecipitates distributed uniformly throughout the matrix of CF8CPWCu, whereas in CF8CPWCu22/17, Cu precipitates were found primarily at the grain boundaries. The presence of these nanoscale Cu-rich particles, in addition to W-rich Cr₂₃C₆, nanoscale Nb carbides, and Z-phase (Nb₂Cr₂N₂), improved the creep strength of the CF8CPWCu steel. Modification of CF8CPWCu with Cr and Ni contents slightly decreased the creep strength but significantly improved the oxidation behavior at 1073 K (800 °C). In particular, the addition of 22Cr and 17.5Ni strongly enhanced the oxidation resistance of the stainless steel resulting in a 100 degrees or greater temperature improvement, and this composition provided the best balance between improving both mechanical properties and oxidation resistance.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1246771
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 47A, Issue 4; ISSN 1073-5623
• Publisher: ASM International
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE