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Title: Development of cast alumina-forming austenitic stainless steels

Abstract

Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt. % are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt. % Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800 C - 850 C in H 2O-, S-, and C- containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromia-forming alloy along with improved oxidation resistance typical of alumina-forming alloys. Lastly, challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Advanced Research Projects Agency - Energy (ARPA-E)
OSTI Identifier:
1362187
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
JOM. Journal of the Minerals, Metals & Materials Society
Additional Journal Information:
Journal Volume: 68; Journal Issue: 11; Journal ID: ISSN 1047-4838
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; austenitic stainless steels; creep; casting; oxidation; alumina

Citation Formats

Muralidharan, G., Yamamoto, Y., Brady, M. P., Walker, L. R., Meyer III, H. M., and Leonard, D. N.. Development of cast alumina-forming austenitic stainless steels. United States: N. p., 2016. Web. doi:10.1007/s11837-016-2094-8.
Muralidharan, G., Yamamoto, Y., Brady, M. P., Walker, L. R., Meyer III, H. M., & Leonard, D. N.. Development of cast alumina-forming austenitic stainless steels. United States. doi:10.1007/s11837-016-2094-8.
Muralidharan, G., Yamamoto, Y., Brady, M. P., Walker, L. R., Meyer III, H. M., and Leonard, D. N.. 2016. "Development of cast alumina-forming austenitic stainless steels". United States. doi:10.1007/s11837-016-2094-8. https://www.osti.gov/servlets/purl/1362187.
@article{osti_1362187,
title = {Development of cast alumina-forming austenitic stainless steels},
author = {Muralidharan, G. and Yamamoto, Y. and Brady, M. P. and Walker, L. R. and Meyer III, H. M. and Leonard, D. N.},
abstractNote = {Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt. % are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt. % Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800 C - 850 C in H2O-, S-, and C- containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromia-forming alloy along with improved oxidation resistance typical of alumina-forming alloys. Lastly, challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.},
doi = {10.1007/s11837-016-2094-8},
journal = {JOM. Journal of the Minerals, Metals & Materials Society},
number = 11,
volume = 68,
place = {United States},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
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  • Efforts at Oak Ridge National Laboratory to developAl2O3-forming austenitic (AFA) stainless steels for high-temperature (600-900 aC) structural use under aggressive oxidizing conditions are overviewed. Data obtained to date indicate the potential to achieve superior oxidation resistance to conventional Cr2O3-forming Fe- and Ni-base heat-resistant alloys, with creep strength comparable to state-of-the-art advanced austenitic stainless steels. Preliminary assessment also indicates the developed alloys are amenable to welding. Details of the alloy design approach and composition-microstructure-property relationships are presented.
  • Creep strengthening of Al-modified austenitic stainless steels by MC carbides or Fe{sub 2}Nb 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 C to 800 C in air and in air with 10 pct water vapor, the alloys exhibited continuous protective Al{sub 2}O{sub 3} 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 {gamma} (fcc) + {alpha} (bcc) dual phase due to the strongmore » {alpha}-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 {gamma}-Fe and still capable of alumina scale formation. Alloys that relied solely on Fe{sub 2}Nb 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 Fe{sub 2}Nb were of limited benefit to creep resistance due to the solution limit of NbC within the {gamma}-Fe matrix of the alloys studied. However, when combined with other MC-type strengtheners, such as V{sub 4}C{sub 3} or TiC, higher levels of creep resistance were obtained.« less
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  • A family of creep-resistant austenitic stainless steels based on alumina (Al2O3) scale formation for superior high-temperature oxidation resistance was recently identified. Results of long-term cyclic oxidation studies (100 h cycles and total exposure duration for up to 7500 h) from 650-800 aC in air and/or air with 10% water vapor for a series of 2.5, 3, and 4 wt.% Al AFA compositions, with varying levels of Nb and Ni additions, are presented. Water vapor was observed to enhance subscale Al consumption in the AFA alloys relative to dry air exposure, presumably via enhanced alumina scale cracking and reformation. Water vapormore » also increased the tendency for internal oxidation. Increased levels of Nb additions were found to significantly improve oxidation resistance, as were reactive element additions of Hf and Y. Computational thermodynamic calculations of the austenitic matrix phase composition and the volume fraction of MC, B2-NiAl, and Fe2Nb base Laves phase precipitates were used to guide interpretation of oxidation behavior alloy composition trends in terms of two-phase oxidation theory, reservoir effect, and the third-element effect of Cr. The implications of these findings for the upper-temperature service limit for this new class of alloys and the potential for AFA alloy modification for increased service temperatures are discussed.« less
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