Aging effects on the mechanical properties of alumina-forming austenitic stainless steels

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2010-03, Vol.527 (7), p.2079-2086
• Main Authors: Bei, H., Yamamoto, Y., Brady, M.P., Santella, M.L.
• Format: Article
• Language: English
• Subjects: Aging; Applied sciences; Cross-disciplinary physics: materials science; rheology; Elasticity. Plasticity; Exact sciences and technology; Fracture; Intermetallics; Materials science; Mechanical characterization; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Physics; Solid solution, precipitation, and dispersion hardening; aging; Steel; Treatment of materials and its effects on microstructure and properties
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2009.11.052

Isothermal aging and tensile evaluation were conducted for recently developed alumina-forming austenitic stainless steels (AFAs). Microstructural observation reveals that NiAl-type B2 and Fe 2(Mo,Nb)-type Laves phase precipitates form as dominant second phases in the austenitic matrix during aging at 750 °C. At room temperature these precipitates increase the strength but decrease the ductility of the AFA alloys. However, when tested at 750 °C, the AFA alloys did not show strong precipitation hardening by these phases, moreover, the elongation to fracture was not affected by aging. Fracture surface and cross-sectional microstructure analysis after tensile testing suggests that the difference of mechanical behaviors between room temperature and 750 °C results from the ductile–brittle transition of the B2 precipitates. At room temperature, B2 precipitates are strong but brittle, whereas they become weak but ductile above the ductile–brittle transition temperature (DBTT).