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.