Abstract
Creep strengthening of Al-modified austenitic stainless steels by MC carbides or Fe2Nb Laves phase was explored. Fe-20Cr-15Ni-(0-8)Al and Fe-15Cr-20Ni-5Al base alloys (at. pct) with small additions of Nb, Mo, W, Ti, V, C, and B were cast, thermally-processed, and aged. On exposure from 650 ° to 800 ° in air and in air with 10 pct water vapor, the alloys exhibited continuous protective Al2O3 scale formation at an Al level of only 5 at. pct (2.4 wt pct). Matrices of the Fe-20Cr-15Ni-5Al base alloys consisted of γ (fcc) + α (bcc) dual phase due to the strong α-Fe stabilizing effect of the Al addition and exhibited poor creep resistance. However, adjustment of composition to the Fe-15Cr-20Ni-5Al base resulted in alloys that were single-phase γ -Fe and still capable of alumina scale formation. Alloys that relied solely on Fe2Nb Laves phase precipitates for strengthening exhibited relatively low creep resistance, while alloys that also contained MC carbide precipitates exhibited creep resistance comparable to that of commercially available heat-resistant austenitic stainless steels. Phase equilibria studies indicated that NbC precipitates in combination with Fe2Nb were of limited benefit to creep resistance due to the solution limit of NbC within the γ-Fe matrix of the alloys studied. However, when combined with other MC-type strengtheners, such as V4C3 or TiC, higher levels of creep resistance were obtained.
Original language | English |
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Pages (from-to) | 2737-2746 |
Number of pages | 10 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 38 A |
Issue number | 11 |
DOIs | |
State | Published - Nov 2007 |
Funding
This research was sponsored by the Office of Fossil Energy, United States Department of Energy, National Energy Technology Laboratory, under Contract No. DE-AC05-00OR22725 with UT–Battelle, LLC. Additional funding and collaboration with the United States DOE Distributed Energy program and the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, are also acknowledged. A portion of this research was conducted at the SHaRE User Facility, Oak Ridge National Laboratory, which is sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences, United States Department of Energy.