Lower critical temperature (A₁) of steel vs. carbon content How does the lower critical temperature (A₁) behave for plain carbon steels as carbon content varies? Choose the correct option.

Concept
The lower critical temperature (A₁) for plain carbon steels is taken as approximately 723–727°C and is commonly treated as essentially constant for these steels in basic metallurgy problems. The upper critical temperature (A₃) decreases with increasing carbon. While Ac₁/Ar₁ can vary slightly with heating/cooling rates, the standard teaching is that A₁ is effectively the same for plain carbon steels.

Final Answer
Is the same for all steels