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Steel at the eutectoid composition: identify the resulting room-temperature microstructure Consider plain carbon steel of eutectoid composition cooled appropriately. Choose the correct phase constitution.

Difficulty: Easy

Wholly pearlite
Wholly austenite
Pearlite and ferrite
Pearlite and cementite

Correct Answer: Wholly pearlite

Explanation:

Concept

Eutectoid composition (≈ 0.76–0.80% C) transforms at 723°C (A₁) to 100% pearlite (lamellae of ferrite + cementite).

Elimination
Below A₁ at room temperature, austenite (b) cannot persist in plain carbon steel.Hypoeutectoid steels contain ferrite + pearlite; hypereutectoid contain pearlite + cementite. Exactly eutectoid is 100% pearlite.

Final Answer
Wholly pearlite

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