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Iron–carbon diagram: select the lower critical temperature (A₁) common to all steels Identify the standard lower critical point for steels on heating/cooling (eutectoid temperature). Choose the correct temperature.

Q: Iron–carbon diagram: select the lower critical temperature (A₁) common to all steels Identify the standard lower critical point for steels on heating/cooling (eutectoid temperature). Choose the correct temperature.

Concept The lower critical temperature A₁, i.e., eutectoid transformation temperature for plain carbon steels, is approximately 723°C. 913°C corresponds to A₃ for pure iron (α→γ transition), not the universal lower critical for steels.

Difficulty: Easy

600°C
700°C
723°C
913°C

Correct Answer: 723°C

Explanation:

Concept

The lower critical temperature A₁, i.e., eutectoid transformation temperature for plain carbon steels, is approximately 723°C.
913°C corresponds to A₃ for pure iron (α→γ transition), not the universal lower critical for steels.

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