This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Austenite is an alloy of iron and carbon with the iron in: \nSelect and explain. \nA. Alpha form, B. Beta form, C. Gamma form, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: At room temperature, pure iron has a body-centered-cubic (bcc) structure. This phase is stable up to 912 °C, where it transforms to a face-centered-cubic (fcc) structure. The solubility of\xa0carbon in bcc is very low and reaches a maximum of\xa0 0.02% at 723°C. This material is known as ferrite.\xa0\xa0\nAbove\xa0723 °C, a solid solution of carbon in an fcc iron matrix called austenite is formed. The maximal solubility of carbon in fcc matrix is 2.1%.\nWhen plain carbon steel containing\xa00.8%\xa0carbon is cooled slowly in the austenitic phase to 723 °C, it undergoes a solid-state eutectoid transformation to yield a microstructural constituent called pearlite, which consists of alternating fine-scale lamellae of ferrite and iron carbide (Fe3C), referred to as cementite, or simply, carbide.\xa0\nThe Fe3C phase is much harder and more rigid than austenite or ferrite.\n\nKey Concept\n\nIt is an interstitial solid of a small of a carbon dissolved in γ iron.\nThe maximum solubility is 2.1%C at 1147o C.\nThe crystal structure of Austenite (γ) is F.C.C.\nHardness – 40 HRC and toughness is high.\n\nRef:Phillips Ed-12th P: 406', 'role': 'assistant'}]