It's seems that addition of carbon atoms increase the hardness by solid solution strengthening. However I do not know why it will have more effect on ferrite than on Austenite.
https://www.doitpoms.ac.uk/tlplib/jominy/uses2.php
Austenite with its CFC structure is more compact than ferrite with a CC structure ,on the other hand, the diffusion coefficient of carbon in austenite is greater than that in ferrite, as well as austenite can dissolve a larger amount of carbon than feriite ;; so how did you find that carbon hardened ferrite more than austenite?
This has to do with where C locates in the different lattices and what distortions this causes, which in turn affects dislocation movement.
In the fcc lattice structure C locates in the rather large octrahedral sites, thus causing less lattice distortion. As such, dislocations are not so much affected by this and the hardening efect is less pronounced.
In the bcc lattice structure C is situated in the much smaller tetrahedral lattice sites. This causes a more severe lattice distortion and stronger interaction with passing dislocations.
- Badges
- Science topic