AskDefine | Define pearlite

Dictionary Definition

pearlite n : a lamellar mixture of cementite and ferrite formed during the cooling of austenite; a micro-constituent of steel and cast iron

Extensive Definition

For the amorphous volcanic glass see perlite.
Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of alpha-ferrite (88 wt%) and cementite (12%) that occurs in some steels and cast irons. It forms by a eutectoid reaction as austenite is slowly cooled below 727°C. The eutectoid composition of Austenite is approximately 0.8% carbon http://www.ariuseickert.com/ScissorTechnicalArticles/EutectoidRegionOfSteel.htm; steel with less carbon content will contain a corresponding proportion of relatively pure ferrite crystallites that do not participate in the eutectoid reaction and cannot transform into pearlite.
The appearance of pearlite under the microscope resembles mother of pearl (also a lamellar structure), from which it takes its name.
A similar structure with lamelle much smaller than the wavelength of visible light lacks this pearlescent appearance. Called bainite, it is prepared by more rapid cooling. Unlike pearlite, whose formation involves the diffusion of all atoms, bainite grows by a displacive transformation mechanism.
pearlite in Bosnian: Perlit (željezo)
pearlite in German: Perlit (Stahl)
pearlite in Modern Greek (1453-): Περλίτης (μεταλλουργία)
pearlite in Persian: پرلیت
pearlite in French: Perlite (acier)
pearlite in Italian: Perlite
pearlite in Hungarian: Perlit (acél)
pearlite in Dutch: Perliet (staal)
pearlite in Japanese: パーライト
pearlite in Polish: Perlit
pearlite in Russian: Перлит
pearlite in Slovak: Perlit (strojárstvo)
pearlite in Turkish: Perlit
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