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Title: High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Materials Letters
Additional Journal Information:
Journal Volume: 195; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 21:31:50; Journal ID: ISSN 0167-577X
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Citation Formats

Hu, Bin, and Baker, Ian. High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels. Netherlands: N. p., 2017. Web. doi:10.1016/j.matlet.2017.02.086.
Hu, Bin, & Baker, Ian. High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels. Netherlands. doi:10.1016/j.matlet.2017.02.086.
Hu, Bin, and Baker, Ian. Mon . "High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels". Netherlands. doi:10.1016/j.matlet.2017.02.086.
title = {High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels},
author = {Hu, Bin and Baker, Ian},
abstractNote = {},
doi = {10.1016/j.matlet.2017.02.086},
journal = {Materials Letters},
number = C,
volume = 195,
place = {Netherlands},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.matlet.2017.02.086

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  • 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
  • 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.
  • A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the {approx}923 K to 1173 K (650 C to 900 C) temperature range due to the formation of a protective Al{sub 2}O{sub 3} scale rather than the Cr{sub 2}O{sub 3} scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerationsmore » of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe{sub 2}(Mo,Nb)-Laves, Ni{sub 3}Al-L1{sub 2}, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.« less
  • The effect of a Zr addition on the precipitation behavior and mechanical properties in Nb-containing alumina-forming austenitic (AFA) stainless steels was investigated using tensile tests, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) analysis. The TEM observation showed that a Zr addition led to the formation of a (Nb,Zr)(C,N) complex particle, which coarsened the Nb-rich carbonitride. Tensile tests were performed at an elevated temperature (700 °C), and both the tensile and yield strengths decreased with a Zr addition. This unexpected result of a Zr addition was due to the reduction of the precipitation strengthening by particle coarsening. -more » Highlights: • The effect of Zr on high temperature strength in AFA steel containing Nb was studied. • Both the tensile and yield strengths of an AFA steel decreased with Zr-addition. • This is due to the reduction of precipitation strengthening by particle coarsening. • Nb(C,N) and (Nb,Zr)(C,N) particles were precipitated in an AFA and Zr-added AFA steel. • The size of (Nb,Zr)(C,N) particle is much bigger than that of Nb(C,N) particle.« less
  • Work in 2007 focused on the development of a new class of heat-resistant austenitic stainless steel alloys which achieved a unique combination of high-temperature creep strength and excellent oxidation resistance via protective Al{sub 2}O{sub 3} scale formation. Strengthening is achieved via the formation of stable nano NbC carbides with/without Fe{sub 2}Nb and related intermetallic phase dispersions, with controlled levels of Al to enable Al{sub 2}O{sub 3} scale formation in both air and air + water vapor environments up to {approx}800-900 C. The developed alloys exhibit comparable creep resistance to that of the best commercial heat-resistant austenitic stainless steels, and themore » protective Al{sub 2}O{sub 3} scale formation provides oxidation resistance superior to that of advanced Cr{sub 2}O{sub 3}-forming heat-resistant austenitic alloys. Preliminary screening also indicated that the developed Al-modified alloys were amenable to welding.« less