True-false Austenite has a FCC crystal structure. The chemical composition of Fe

Question

True-false Austenite has a FCC crystal structure. The chemical composition of Fe_3C can be anything between 2.14 and 6.70 wt% C. 1030 steel is hypereutectoid. The Fe-FejC system has three important phase reactions: one peritectic, one eutectic, and one eutectoid. A 1030 steel cooled from the austenite phase field to the ferrite field would have ferrite, eutectoid ferrite, and present in the final microstructure. Eutectic solder alloys are typically stronger than hypo- or hyper-cutectoid solders in the same system. Metastable systems are time independent and are obtained during equilibrium condition. Steel alloys are commonly divided into families such as low-carbon or medium-carbon based on the amount of carbon in the steel.

Explanation / Answer

a) True: It is a metallic, nonmagnetic allotrope of iron or a solid solution of iron with carbon.

b) True: Cast iron contains 2.14-6.70 wt% C. Commercial cast iron typically contain < 4.5 wt%. At 6.7 wt% C, the iron carbide intermediate compound (Fe3C) is known as cementite.

c) False: Hypereutectoid steel has greater than 0.8% C. But 1030 steel has 0.28-0.34% C. 1030 steel is hot rolled and cold drawn.

d) True:

Eutectic or invariant point. Liquid and two solid phases exist in equilibrium at the eutectic composition and the eutectic temperature.

The eutectoid reaction occurs from one solid phase to two new solid phases. It also shows as V on top of a horizontal line in the phase diagram.

Solid Phase 1 ------> Solid Phase 2 + Solid Phase 3

The peritectic reaction also involves three solid in equilibrium, the transition is from a solid + liquid phase to a different solid phase when cooling. The inverse reaction occurs when heating.

Solid Phase 1 + liquid ----------> Solid Phase 2

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