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

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Metallurgical and Materials Transactions A

DOI:https://doi.org/10.1007/s11661-009-9886-1· OSTI ID:979097

Yamamoto, Yukinori ^[1]; Santella, Michael L ^[1]; Brady, Michael P ^[1]; Bei, Hongbin ^[1]; Maziasz, Philip J ^[1]

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1. ORNL

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), M{sub 23}C{sub 6} (M: mainly Cr), B2 [{beta}-(Ni,Fe)Al], and Laves [Fe{sub 2}(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 M{sub 23}C{sub 6}. 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.

• Research Organization: Oak Ridge National Laboratory (ORNL); Shared Research Equipment Collaborative Research Center
• Sponsoring Organization: FE USDOE - Office of Fossil Energy (FE)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 979097
• Journal Information: Metallurgical and Materials Transactions A, Journal Name: Metallurgical and Materials Transactions A Journal Issue: 8 Vol. 40A
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALLOYS
CREEP
LAVES PHASES
PRECIPITATION
STABILITY
STABILIZATION
STAINLESS STEELS
TESTING
THERMODYNAMICS