Formation and Growth of Pearlite
At eutectoid point, austenite is an interstitial solid solution having 0.8 percent carbon dissolved in f.c.c. iron. Ferrite, however, is b.c.c. iron and dissolves very little carbon. So, the change in crystal cannot occur until the carbon atoms come out of solution. Therefore, the first step is the precipitation of the carbon atoms to form plates of cementite (iron carbide). In the area immediately adjacent to the cementite plate the iron is depleted of carbon, and the atoms may now rearrange themselves to form b.c.c. ferrite. Thin layers of ferrite are formed on each side of the cementite plate. The process continues by the formation of alternate layers of cementite and ferrite to give the fine fingerprint mixture known as pearlite.
Formation and Growth of PearliteAt eutectoid point, austenite is an interstitial solid solution having 0.8 percent carbon dissolved in f.c.c. iron. Ferrite, however, is b.c.c. iron and dissolves very little carbon. So, the change in crystal cannot occur until the carbon atoms come out of solution. Therefore, the first step is the precipitation of the carbon atoms to form plates of cementite (iron carbide). In the area immediately adjacent to the cementite plate the iron is depleted of carbon, and the atoms may now rearrange themselves to form b.c.c. ferrite. Thin layers of ferrite are formed on each side of the cementite plate. The process continues by the formation of alternate layers of cementite and ferrite to give the fine fingerprint mixture known as pearlite.
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