Formation Mechanism 上游克通大粤 SHANGHAI JIAO TONG UNIVERSITY 1.Austenite Nucleation Local variation of energy,composition,and crystal structure 1538 A8+L 1495℃ Maximum C concentration in ferrite: 1500 0.02% L 1394 C concentration required to transform Y+L 1227℃ ferrite to austenite is: 1148℃ L+Fe;C >0.77%at727℃ Y E >0.66%at740℃ 000 >0.40%at780℃ 912 Y+Fe;C I Acml >0.32%at800℃ 1727℃(A) >All much larger than that in ferrite P I a+Fe;C 500 00.02 0.77 2.11 4.30 6.69 Fe C Concentration / Fe;C K.Chen 13K. Chen Formation Mechanism 13 1. Austenite Nucleation Local variation of energy, composition, and crystal structure  Maximum C concentration in ferrite: 0.02%  C concentration required to transform ferrite to austenite is:  0.77% at 727℃  0.66% at 740℃  0.40% at 780℃  0.32% at 800℃  All much larger than that in ferrite C Concentration /% Temperature /ºC