– Upper critical temperature (point) A3 is the temperature, below which ferrite starts to form as a result of ejection from austenite in the hypo-eutectoid alloys.
– Upper critical temperature (point) ACM is the temperature, below which cementite starts to form as a result of ejection from austenite in the hyper-eutectoid alloys.
– Lower critical temperature (point) A1 is the temperature of the austenite-to-Pearlite eutectoid transformation. Below this temperature austenite does not exist.
– Magnetic transformation temperature A2 is the temperature below which α-ferrite is ferromagnetic.
