pearlite

The eutectoid steel is heated and fully austenitized, then cooled slowly, and eutectoid decomposition occurs at a temperature slightly lower than A1. The product is a mixture of & alpha; and Fe3C. It is called pearlite because of its image like mother of Pearl under the microscope.            Lamellar pearlite can be divided into pearlite, sorbite and troostite according to the size of lamellar spacing.            Generally, the so-called lamellar pearlite refers to the pearlite formed in the temperature range of a1-650 ℃, which can clearly distinguish the lamellar structure of ferrite and cementite under the optical microscope, and its lamellar spacing is about 150-450 nm. Under the optical microscope, the pearlite of the lamellae can be distinguished obviously, and the lamellar spacing is about 150-450 nm.            The pearlite formed in the temperature range of 650-600 ℃ has a small plate spacing of about 80-150nm. The lamellar morphology of ferrite and cementite can only be distinguished under a high-power optical microscope (when the magnification is 800-1500 times). This kind of lamellar pearlite is called sorbite. When the film spacing is 80-150 nm, it is called sorbite, and the film layer is difficult to be distinguished under optical microscope.            The pearlite formed in the temperature range of 600-550 ℃ has very fine lamellar spacing, about 30-80nm. Under the optical microscope, the lamellar characteristics can not be distinguished at all. Only under the electronic microscope can it be distinguished. This kind of very fine pearlite is called troostite. The pearlite with 30-80nm spacing formed at lower temperature is called troostite. The lamellar structure can only be observed under electron microscope.            When cementite exists on ferrite matrix in granular form, it is called granular pearlite. Granular pearlite can be obtained by the decomposition of inhomogeneous austenite during slow cooling, or by other heat treatment methods.