Effect of alloying additions on phase equilibria and creep resistance of alumina-forming austenitic stainless steels

Y. Yamamoto; M. L. Santella; M. P. Brady; H. Bei; P. J. Maziasz

doi:10.1007/s11661-009-9886-1

Effect of alloying additions on phase equilibria and creep resistance of alumina-forming austenitic stainless steels

Y. Yamamoto, M. L. Santella, M. P. Brady, H. Bei, P. J. Maziasz

Alloy Behavior & Design

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Abstract

The high-temperature creep properties of a series of alumina-forming austenitic (AFA) stainless steels based on Fe-20Ni-(12-14)Cr-(2.5-4)Al-(0.2-3.3)Nb-0.1C (weight percent) were studied. Computational thermodynamics were used to aid in the interpretation of data on microstructural stability, phase equilibria, and creep resistance. Phases of MC (M: mainly Nb), M₂₃ C₆ (M: mainly Cr), B2 [β-(Ni,Fe)Al], and Laves [Fe₂(Mo,Nb)] were observed after creep-rupture testing at 750 °C and 170 MPa; this was generally consistent with the thermodynamic calculations. The creep resistance increased with increasing Nb additions up to 1 wt pct in the 2.5 and 3 Al wt pct alloy series, due to the stabilization of nanoscale MC particles relative to M₂₃C₆. Additions of Nb greater than 1 wt pct decreased creep resistance in the alloy series due to stabilization of the Laves phase and increased amounts of undissolved, coarse MC, which effectively reduced the precipitation of nanoscale MC particles. The additions of Al also increased the creep resistance moderately due to the increase in the volume fraction of B2 phase precipitates. Calculations suggested that optimum creep resistance would be achieved at approximately 1.5 wt pct Nb in the 4 wt pct Al alloy series.

Original language	English
Pages (from-to)	1868-1880
Number of pages	13
Journal	Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume	40
Issue number	8
DOIs	https://doi.org/10.1007/s11661-009-9886-1
State	Published - 2009

Funding

The authors thank E.P. George, C.T. Liu, and J.H. Schneibel for helpful comments on this manuscript. This work was funded by the United States Department of Energy (USDOE) Fossil Energy Advanced Research Materials program. The Oak Ridge National Laboratory is managed by UT–Battelle, LLC (Oak Ridge, TN), for the USDOE under Contract No. DE-AC05-00OR22725. The authors also acknowledge the SHaRE User Facility at the Oak Ridge National Laboratory, sponsored by the USDOE Office of Basic Energy Sciences, Division of Scientific User Facilities.

Funders	Funder number
Division of Scientific User Facilities
Fossil Energy Advanced Research Materials
USDOE Office of Basic Energy Sciences
United States Department of Energy
Oak Ridge National Laboratory

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title = "Effect of alloying additions on phase equilibria and creep resistance of alumina-forming austenitic stainless steels",

abstract = "The high-temperature creep properties of a series of alumina-forming austenitic (AFA) stainless steels based on Fe-20Ni-(12-14)Cr-(2.5-4)Al-(0.2-3.3)Nb-0.1C (weight percent) were studied. Computational thermodynamics were used to aid in the interpretation of data on microstructural stability, phase equilibria, and creep resistance. Phases of MC (M: mainly Nb), M23 C6 (M: mainly Cr), B2 [β-(Ni,Fe)Al], and Laves [Fe2(Mo,Nb)] were observed after creep-rupture testing at 750 °C and 170 MPa; this was generally consistent with the thermodynamic calculations. The creep resistance increased with increasing Nb additions up to 1 wt pct in the 2.5 and 3 Al wt pct alloy series, due to the stabilization of nanoscale MC particles relative to M23C6. Additions of Nb greater than 1 wt pct decreased creep resistance in the alloy series due to stabilization of the Laves phase and increased amounts of undissolved, coarse MC, which effectively reduced the precipitation of nanoscale MC particles. The additions of Al also increased the creep resistance moderately due to the increase in the volume fraction of B2 phase precipitates. Calculations suggested that optimum creep resistance would be achieved at approximately 1.5 wt pct Nb in the 4 wt pct Al alloy series.",

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Effect of alloying additions on phase equilibria and creep resistance of alumina-forming austenitic stainless steels

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