Austenite发表评论(0)编辑词条

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 the carbon diffuses. Depending on alloy composition and rate of cooling, pearlite may form. If the rate of cooling is very fast, the alloy may experience a large lattice distortion known as martensitic transformation, instead of transforming into ferrite and cementite. In this industrially very important case, the carbon is not allowed to diffuse due to the cooling speed, resulting in a BCC-structure. 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 tempered martensite. If a low-hardenability steel is quenched, a significant amount of austenite will be retained in the microstructure.
Stabilization
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).

　　奥氏体英文名称：austenite
　　晶体结构：面心立方（fcc）
　　字母代号：A、γ
　　定 义：碳在γ－Fe中形成的间隙固溶体
　　性能特点：奥氏体是一种塑性很好，强度较低的固溶体，具有一定韧性。不具有铁磁性。因此，分辨奥氏体不锈钢刀具(常见的18－8型不锈钢）的方法之一就是用磁铁来看刀具是否具有磁性。
　　古代铁匠打铁时烧红的铁块既处于奥氏体状态。
　　另外，奥氏体因为是面心立方，四面体间隙较大，可以容纳更多的碳。