Austenite

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Definition - What does Austenite mean?

Austenite is a metallic non-magnetic allotrope of iron with an alloying element. In plain-carbon steel, austenite exists far above the critical eutectoid temperature of 1000°K.

It is a solid solution created when carbon steel is heated to red hot. It is also known as gamma phase iron. During cooling of the steel, it can transform into pearlite or ferrite. This gamma form of iron is exhibited by the most common type of stainless steel used in hospital and food-service equipment.

It is named after Sir William Chandler Roberts-Austen (1843-1902), an English metallurgist.

Corrosionpedia explains Austenite

Austenite is a metallic, non-magnetic solid solution of carbon and iron that exists in steel above the critical temperature of 1333°F (723°C). Its face-centered cubic (FCC) structure allows it to hold a high proportion of carbon in solution. During cooling, this structure either breaks down into a mixture of ferrite and cementite (usually in the structural forms pearlite or bainite), or undergoes a slight lattice distortion known as martensitic transformation.

The rate of cooling is a determining factor for relative proportions of these materials and therefore the mechanical properties (e.g. hardness, tensile strength) of the steel. The introduction of certain other metals, such as manganese and nickel, can stabilize the austenitic structure, facilitating heat-treatment of low-alloy steels. These elements are referred to as austenite stabilizers. Elements like silicon, molybdenum and chromium tend to de-stabilize austenite, raising the eutectoid temperature.

Austenite can contain far more carbon than ferrite, between 0.8% at 1333°F (723°C) and 2.08% at 2098°F (1148°C). Thus, above the critical temperature, all of the carbon contained in ferrite and cementite (for a steel of 0.8% C) is dissolved in the austenite. Since austenite steel holds a greater amount of dissolved carbon, it exhibits increased formability.

The phase at which solid steel recrystallizes and has a face-centered cubic crystal structure is known as austenite phase. From 1674 to 2541°F (912 to 1394°C) alpha iron undergoes a phase transition from body-centered cubic (BCC) to the face-centered cubic (FCC) configuration of gamma iron, also called austenite.

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