Creep and Oxidation Behavior of Modified CF8C-Plus with W, Cu, Ni, and Cr

Kinga A. Unocic; Sebastien Dryepondt; Yukinori Yamamoto; Philip J. Maziasz

doi:10.1007/s11661-016-3348-3

Creep and Oxidation Behavior of Modified CF8C-Plus with W, Cu, Ni, and Cr

Kinga A. Unocic, Sebastien Dryepondt, Yukinori Yamamoto, Philip J. Maziasz

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Abstract

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.

Original language	English
Pages (from-to)	1641-1653
Number of pages	13
Journal	Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume	47
Issue number	4
DOIs	https://doi.org/10.1007/s11661-016-3348-3
State	Published - Apr 1 2016

Funding

The authors would like to thank G.W. Garner, T.M. Lowe, T. Geer, J.L. Moser, and K.A. Powers for assistance with the experimental work. B.A Pint, L. F. Allard, and R.R. Unocic provided helpful comments and suggestions on the results and manuscript. Research was supported by the U.S. Department of Energy, Office of Coal and Power R&D, Office of Fossil Energy, Office of Coal and Power R&D in the Office of Fossil Energy, and microscopy was supported through a user proposal by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility.

Funders	Funder number
CNMS
ORNL’s Center for Nanophase Materials Sciences
Office of Coal and Power R&D
U.S. Department of Energy
Office of Fossil Energy
Office of Science

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10.1007/s11661-016-3348-3

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title = "Creep and Oxidation Behavior of Modified CF8C-Plus with W, Cu, Ni, and Cr",

abstract = "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.",

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Creep and Oxidation Behavior of Modified CF8C-Plus with W, Cu, Ni, and Cr

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