Pearlite


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Related to Pearlite: Bainite, cementite

pearlite

[′pər‚līt]
(geology)
(metallurgy)
A lamellar aggregate of ferrite (almost pure iron) and cementite (Fe3C) often occurring in carbon steels and in cast iron.

Pearlite

 

(in metallurgy), a structural component of iron-carbon alloys (steels and cast irons) that consists of a eutectic mixture of two phases, ferrite and cementite. In alloy steels the two phases that combine to form pearlite are different carbides.

Pearlite is a product of the eutectic decomposition of austenite upon relatively slow cooling of iron-carbon alloys below 723°C. In this process, γ-iron is transformed into α-iron, in which the solubility of carbon is only about 0.02 percent. The excess carbon precipitates as cementite or carbides.

A distinction is made between lamellar and granular pearlite. In the former, which is more common, both phases are present as lamellas; in the latter, rounded granules, or globules, of cementite are arranged against a background of ferrite globules. As supercooling proceeds, the number of pearlite colonies increases; that is, the number of sections of the piece of metal in which ferrite and cementite or carbide lamellas are uniformly oriented increases. Furthermore, the lamellas of pearlite become thinner as the temperature drops.

The mechanical properties of pearlite depend primarily on the interlamellar distance, that is, the total thickness of the two adjacent lamellas. Decreasing this distance increases ultimate strength and yield strength and decreases the ductile-to-brittle transition critical temperature. The structure of pearlite facilitates mechanical working of steel. Certain dispersed varieties of pearlite are sometimes called sorbite or troostite.

REFERENCE

Bunin, K. P., and A. A. Baranov. Metallografiia. Moscow, 1970.

R. I. ENTIN

perlite

A siliceous volcanic rock; under heat it expands to 15 to 20 times its original volume, forming an excellent lightweight aggregate; used in plaster or gypsum wallboard, as loose-fill thermal insulation, and as an aggregate in concrete.
References in periodicals archive ?
Weld metal consisting of ledeburitic carbide with some amount of alloyed pearlite microstructure have attributed higher hardness than PMZ which show lesser amount of coarser ledeburitic carbide and higher amount of pearlite than weld metal.
Embury, "Fracture of steels containing pearlite," Metallurgical Transactions, vol.
The microstructural results showed that the coarsened polygonal ferrite and pearlite were obtained in the weld seam, whereas no obvious oxide and other inclusions were observed (Figure 2).
Sequence 2--Post-compression condition, strain rate of [10.sup.-3] [s.sup.-1]--martensitic-bainitic microstructure with a small volume fraction of pearlite and retained austenite--scanning electron micrograph
Structure is more even, consists of ferrite and pearlite, therefore it is possible to observe several microstructural inhomogeneities.
HAZ presents mainly pearlite grains, shown to be affected by the heat produced during the welding process.
Figure 5(a) shows the microstructure for the original specimen, which shows the microstructure was ferrite in the parent and pearlite phases (black) [13, 14], and the pearlite phase had a density of 24.36% and distribution in the parent phase.
Tool life showed a better wear performance and surface finish in the cast iron inoculated with IMSR75, since the presence of strontium increased the number of eutectic cells with finer pearlite and graphite.
Cement, sand, aggregates, Fly ash concrete block: Cement, fly ash, aggregates, Lightweight concrete hollow block: Cement, lightweight aggregate, such as, fly ash, ceramisite, pumice, furnace slag, cinder, pearlite and other waste slag.
The local cooling rate of the material during the manufacturing process may also influence the spacing of the pearlite lamellae, with a smaller spacing corresponding to a higher hardness.