Bainite
Encyclopedia : B : BA : BAI : Bainite
| Iron alloy phases |
|---|
|
Austenite (γ-iron; hard) Bainite Martensite Cementite (iron carbide; Fe3C) Ferrite (α-iron; soft) Pearlite (88% ferrite, 12% cementite) |
| Types of Steel |
|
Plain-carbon steel (up to 2.1% carbon) Stainless steel (alloy with chromium) HSLA steel (high strength low alloy) Tool steel (very hard; heat-treated) |
| Other Iron-based materials |
|
Cast iron (>2.1% carbon) Wrought iron (almost no carbon) Ductile iron |
Bainite is a mostly metallic substance that exists in steel after certain heat treatments. First described by Davenport E. S. and Edgar Bain, it forms when austenite (a solution of carbon in iron) is rapidly cooled past a critical temperature of 1333°F (about 723°C).
A fine non-lamellar structure, bainite commonly consists of ferrite and cementite. It is similar in constitution to pearlite, but with the ferrite forming by a displacive mechanism similar to martensite formation, usually followed by precipitation of carbides from the supersaturated ferrite or austenite.
When formed during continuously cooling, the cooling rate to form bainite is higher than that required to form pearlite, but lower than that to form martensite, in steel of the same composition.
Bainite is generally stronger and more ductile than pearlite.
External links
- [Free online textbook devoted to bainite], from Cambridge University Press and the Institute of Materials
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