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Published on: September 23, 2018
Creep-resistant, Al2O3-forming austenitic stainless steels
Y Yamamoto1, M P Brady, Z P Lu
1Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6115, USA.
Science (New York, N.Y.)
|April 21, 2007
Summary
New austenitic stainless steels offer enhanced high-temperature performance. These cost-effective alloys provide superior creep strength and oxidation resistance for energy applications.
Area of Science:
- Materials Science
- Metallurgy
- High-Temperature Alloys
Background:
- Developing advanced materials for high-temperature applications is crucial for improving energy conversion efficiency and component longevity.
- Existing high-strength steels often face limitations in aggressive oxidizing environments and at elevated operating temperatures.
- Austenitic stainless steels are desirable for their mechanical properties but require enhancements for extreme conditions.
Purpose of the Study:
- To develop a new family of cost-effective, high-creep strength austenitic stainless steels capable of forming protective alumina (Al2O3) scales.
- To enable higher operating temperatures for structural components in demanding energy-conversion systems.
- To investigate the effects of specific alloying elements on creep resistance and oxidation behavior.
Main Methods:
- Alloy design based on Fe-20Ni-14Cr-2.5Al (weight percent) composition.
- Strengthening achieved through nanodispersions of niobium carbide (NbC).
- Elimination of titanium and vanadium to facilitate Al2O3 scale formation and stabilize the austenitic matrix.
- Testing of creep-rupture lifetime and oxidation resistance under various high-temperature conditions.
Main Results:
- Demonstrated creep-rupture lifetime exceeding 2000 hours at 750°C and 100 MPa in air.
- Achieved protective Al2O3 scale formation with reduced aluminum content compared to previous alloys.
- Exhibited resistance to oxidation in air with 10% water vapor at both 650°C and 800°C.
- Stabilization of the austenitic matrix structure was confirmed.
Conclusions:
- The developed inexpensive, Al2O3-forming austenitic stainless steels exhibit excellent creep strength and oxidation resistance.
- These alloys have significant potential for increasing operating temperatures of structural components in energy-conversion systems.
- Optimized alloy composition, particularly the reduction of Al and elimination of Ti/V, is key to achieving superior high-temperature performance.
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