Question

. Line Acm on Iron-iron-carbide diagram indicates
1) the beginning of transition from austenite
to ferrite
2) completion of austenite transition to ferrite and
pearlite
3) limit of carbon solubility in austenite
4) all of these​

Answer 1

Acm line illustrates that solid solubility of carbon in austenite decreases very rapidly from a maximum of 2.14 % at 1148 deg C to a maximum of 0.76 % at 727 deg C, due to greater stability of cementite at lower temperatures.