Metallurgy and Phase Diagrams Flashcards
6 cards from real ME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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On the iron-iron carbide (Fe-Fe3C) phase diagram, what is the carbon content at the eutectoid composition?
Answer: 0.76 wt% C
The eutectoid point in the Fe-Fe3C system occurs at 0.76 wt% C and 727°C, where austenite transforms to pearlite upon slow cooling.
Pearlite is a microstructure consisting of alternating lamellae of:
Answer: Ferrite and cementite
Pearlite forms by the eutectoid reaction and consists of alternating layers of alpha-ferrite and cementite (Fe3C).
Martensite in steel is formed by:
Answer: Rapid quenching of austenite, preventing diffusion-based transformation
Martensite forms by a diffusionless shear transformation when austenite is quenched too rapidly for carbon to diffuse, trapping carbon in a body-centered tetragonal structure.
The Gibbs phase rule for a system in equilibrium is expressed as:
Answer: F = C - P + 2
The Gibbs phase rule F = C - P + 2 relates degrees of freedom (F), components (C), and phases (P) at equilibrium.
In a binary phase diagram, the lever rule is used to determine:
Answer: The relative amounts (fractions) of each phase in a two-phase region
The lever rule applies the principle of mass balance to calculate the weight fractions of each phase present in a two-phase region of a phase diagram.
Normalizing a steel involves:
Answer: Heating to the austenite region and air cooling
Normalizing heats steel into the austenite phase field and then allows it to air cool, producing a fine, uniform microstructure.