Austenite

Austenite (or gamma phase iron) is a metallic non-magnetic solid solution of iron and an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (about 727 °C); other alloys of steel have different eutectoid temperatures. It is named after Sir William Chandler Roberts-Austen (1843-1902).

Behavior in Plain-Carbon Steel

As austenite cools, it often transforms into a mixture of ferrite and cementite as dissolved carbon falls out of solution. Depending on alloy composition and rate of cooling, pearlite may form. If the rate of cooling is very fast, the alloy may experience a slight lattice distortion known as martensitic transformation, instead of transforming into a mixture. In this industrially very important case, the carbon is not allowed to blend out in the remaining melt due to the cooling speed, but is captured inside the FCC-structure of austenite, creating tension in the crystal when the alloy cools. The result is hard martensite. The rate of cooling determines the relative proportions of these materials and therefore the mechanical properties (e.g. hardness, tensile strength) of the steel. Quenching (to induce martensitic transformation), followed by tempering will transform some of the brittle martensite into bainite. If a low-hardenability steel is quenched, a significant amount of austenite will be retained in the microstructure.

tabilization

The addition of certain alloying elements, such as manganese and nickel, can stabilize the austenitic structure, facilitating heat-treatment of low-alloy steels. In the extreme case of austenitic stainless steel, much higher alloy content makes this structure stable even at room temperature. On the other hand, such elements as silicon, molybdenum, and chromium tend to de-stabilize austenite, raising the eutectoid temperature.

Austenite transformation and Curie point

In many magnetic alloys, the Curie point, the temperature at which magnetic materials cease to behave magnetically, occurs at nearly the same temperature as the austenite transformation. This behavior is attributed to the paramagnetic nature of austenite, while both martensite and ferrite are strongly ferromagnetic.

Thermo-optical emission

A blacksmith causes phase changes in the iron-carbon system in order to control the material's mechanical properties, often using the annealing, quenching, and tempering processes. In this context, the color of light emitted by the workpiece is an approximate gauge of temperature, with the transition from red to orange corresponding to the formation of austenite in medium- and high-carbon steel.

Maximum carbon solubility in austenite is 2.03% C at 1420 K (1147 °C).

ee also

*Cementite
*Eutectoid
*Ferrite (iron)
*Martensite

References

* Reed-Hill, Robert, and Reza Abbaschian. "Physical Metallurgy Principles", 3rd Edition. Boston: PWS-Kent Publishing, 1991. ISBN 0534921736.

External links

* [http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/examples/kimcon.html Fe-Fe3C phase diagram]


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Look at other dictionaries:

  • austénite — [ ɔstenit ] n. f. • 1903; de Austen, métallurgiste angl. ♦ Métall. Constituant micrographique des aciers (à face cubique centrée) contenant une solution d environ 2% de carbone. ⇒ ferrite. ● austénite nom féminin (de Austen, nom propre)… …   Encyclopédie Universelle

  • Austenite — Austénite Cet article est lié aux composés du fer et du carbone Fer Carbone …   Wikipédia en Français

  • austenite — n. (Metallurgy) [From W. C. Roberts Austen, an English metallurgist.] a solid solution of ferric carbide or carbon in iron; it cools to form pearlite or martensite. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • Austenite — Austenite. См. Ayстенит. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • austenite — [ôs′tən īt΄] n. [Fr, after Sir Wm. C. Roberts Austen (1843 1902), Eng metallurgist] a nonmagnetic solid solution of carbon or iron carbide in some iron, obtained in high carbon steels by rapid quenching and deformation at high temperatures …   English World dictionary

  • Austénite — Cet article est lié aux composés du fer et du carbone Fer Carbone Phases …   Wikipédia en Français

  • Austenite — noun a fan or admirer of ; someone who studies the works of Jane Austen. [I]t seems a pity that they should not form a volume in one of the neat series of Jane Austens novels now published, as to a real Austenite they contain much that is… …   Wiktionary

  • austenite — /aw steuh nuyt /, n. Metall. 1. a solid solution of carbon or of carbon and other elements in gamma iron, having a face centered cubic lattice at all temperatures. 2. an allotrope of iron, stable between 910°C and 1400°C and having a face… …   Universalium

  • austenite — /ˈɒstənaɪt/ (say ostuhnuyt) noun a solid solution of one or more elements in face centred cubic iron; unless otherwise designated (such as nickel austenite) the solute is generally assumed to be carbon. {named after Sir WC Roberts Austen,… …   Australian English dictionary

  • austenite — austenitas statusas T sritis chemija apibrėžtis Homogeninė plieno fazė, kurioje gali būti iki 2,14% anglies ir kuri išlieka >727 °C temperatūroje. atitikmenys: angl. austenite rus. аустенит …   Chemijos terminų aiškinamasis žodynas

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