Composition: Carbon steel (1,3%C, hypereutectoid).

Processing: Hot-rolled. Furnace cooling from 970ºC.

Etching: 10-15 s immersion in 2% nital.

This is a hypereutectoid steel and, therefore, with higher carbon content than specimens X17 and X18. At 970ºC, the material is in the austenitic field (see phase Fe-Fe₃C diagram). During slow cooling in the furnace, primary or proeutectoid cementite precipitates along the grain boundaries of austenite. This precipitation reduces the amount of C in austenite until it reaches 0.8 %C, where it transforms to ferrite and cementite in a lamellar arrangement known as pearlite. The lamellae of ferrite and cementite are readily visible in the micrographs.

Fe-Fe₃C diagram

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