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Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5 wt%) and cementite (12.5 wt%) that occurs in some steels and cast irons. During slow cooling of an iron-carbon alloy, pearlite forms by a eutectoid reaction as austenite cools below 723 °C (1,333 °F) (the eutectoid temperature).
Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.
Being about twice the diameter of the tetrahedral hole, the carbon introduces a strong local strain field. Mild steel (carbon steel with up to about 0.2 wt% C) consists mostly of α-Fe and increasing amounts of cementite (Fe 3 C, an iron carbide). The mixture adopts a lamellar structure called pearlite.
Every gardener wants nutrient-rich soil. But just because your yard doesn’t have enough nutrients naturally doesn’t mean you can’t add more with the help of vermiculite or perlite, common ...
Normalized steel consists of pearlite, martensite, and sometimes bainite grains, mixed together within the microstructure. This produces steel that is much stronger than full-annealed steel, and much tougher than tempered quenched steel. However, added toughness is sometimes needed at a reduction in strength.
The pearlite takes on longer, deeper scratches, and either appears shiny and bright, or sometimes dark depending on the viewing angle. The martensite is harder to scratch, so the microscopic abrasions are smaller. The martensite usually appears brighter yet flatter than the pearlite, and this is less dependent on the viewing angle. [12]
A very rapid quench is essential to create martensite. For a eutectoid carbon steel of thin section, if the quench starting at 750 °C and ending at 450 °C takes place in 0.7 seconds (a rate of 430 °C/s) no pearlite will form, and the steel will be martensitic with small amounts of retained austenite. [2]
Perlite (volcanic glass) Phengite (variety of muscovite) Phosphorite (name given to impure, massive apatite.) Pimelite; Pitchblende (a massive impure form of uraninite) Plessite (mixture of kamacite and taenite) Potassium alum or potash alum (as a mineral, is called alum-(K))