It seems that we have a perennial notion of relation Austentite and Ferrite in Fe-C phase diagram however we refer to them as gamma or alpha iron.Is having a minimal carbon content necessary for this polymorph to exist can we have other alloying elements instead of Carbon?
Existence of ferrite (alpha or gamma) and austenite is independent of carbon content. However, the amount of carbon can control the temperature range of phase stability.
Those phases are present in the phase diagram even at 0%C, so there's no question about their existence in pure iron. The austenite/ferrite transformation does not require carbon, unlike the martensitic transformation in the same system. Gamma and alpha iron are just traditional names used for convenience.
No. it is not possible to get these phases without solubility of carbon
It is a question of terminology. If we speak about words ferrite and austenite we really means the structure of steel, and some ammount of carbon is dissolved in fe with fcc and bcc structure correspondingly. we did not use these terms for pure Fe or Fe based alloys without carbon. on phase diagrames we peaple wrote the name of the phase with the use greek and by these way they indicate the crystal structure... It was common... nowadays it is not exactly so and smtimes one prefer indicate as bcc-Fe, fcc-Cu, hcp-Ti without indication solutions
Shunmugasundaram Natarajan - https://www.tandfonline.com/doi/full/10.1080/14786430410001663178
https://www.ispatguru.com/pure-iron/
The short answer is yes. Austenite is stable between 1394 °C and 912 °C at 0% C, at a lower temperature ferrite is the more stable phase. You can see that in the Fe-C diagram.
We talk about Carbon a lot when it comes to these phases not just because of the different solubility limits but also because of the fact that Carbon is an austenite stabilizer. You can see that in the Fe-C diagram as well: the more %C you have the more stable austenite is at lower temperatures, until it reaches the A1 temperature that is, where ferrite becomes the more stable phase and the excess carbon forms carbides such as cementite (iron carbides) or chromium carbides.
Existence of ferrite (alpha or gamma) and austenite is independent of carbon content. However, the amount of carbon can control the temperature range of phase stability.
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