X20
Carbon steel (1.3%C) Annealed
![](/data/cont/docs/2468-2022-07-11-naranja web56.jpg)
![](/data/cont/docs/2468-2022-07-11-verde web66.jpg)
![](/data/cont/docs/2468-2022-07-11-azul web90.jpg)
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
![](/data/cont/docs/2468-2022-07-14-Fe-Fe3C82.png)
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