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.
Mechanical Engineering
Engineering Materials
Difficulty: Easy
Choose an option
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AWholly pearlite
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BWholly austenite
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CPearlite and ferrite
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DPearlite and cementite
Answer
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).
EliminationBelow 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 AnswerWholly pearlite