2090 – 05 – When Does Pearlite Form?

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At room temperature, steel contains both ferrite and cementite. As steel cools from the cementite to the austenite phase, part of the ferrite and cementite turns into pearlite. Pearlite has equal rows of ferrite and cementite. Austenite will become pearlite in between 1000 and 1341 degrees Fahrenheit.
Pearlite formation occurs differently in hypoeutectoid and hypereutectoid steels. Since hypoeutectoid steel has less carbon, it forms ferrite first. The rest of the austenite will change to pearlite when temperatures are below 1341 Fahrenheit. This creates steel with a mix of ferrite and pearlite.
Hypereutectoid steels have more carbon content, so cementite makes at austenite grain boundaries at the start of the cooling process. When steel dips below the eutectic temperature, the last parts of austenite will change to pearlite, creating a mixture of pearlite and cementite.