上海交通大学：《材料加工原理 Principles of Materials Processing》教学资源（课程讲稿）金属材料热处理原理 Heat Treatment Principles of Metals Chapter 9 Eutectoid and Reverse Eutectoid

Intro to Austenite h 上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY 1538 Aδ+L 1495℃ 1500 B 1394 L Y+L 1227℃ 1148℃ C L+Fe:C Y E Mother of pearl 1000 G I 912 Y+Fe;C As Acml I727C(A1) AP 1 +FeC I 1 500 I L 00.02 0.77 2.11 4.30 6.69 Fe Fe;C C Concentration / Pearlite K.Chen 6

K. Chen Intro to Austenite 6 C Concentration /% Temperature /ºC Pearlite Mother of pearl

Intro to Austenite 上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY Actual transformation temperatures: Y Heating:Aci,Ac3,Accm ACcm ACm G Cooling:Ari,Ar3,Arcm a+y Y+Fe;C Ac stands for arret chauffant (stop heating) A,stands for arret refroidissement(stop &+Fe;C cooling) Q wcX100 K.Chen 7

K. Chen Intro to Austenite 7 Actual transformation temperatures: - Heating: ACl, AC3, Accm - Cooling: Arl,Ar3, Arcm 𝜶𝜶 + 𝜸𝜸Temperature /ºC - Ac stands for arret chauffant (stop heating) - Ar stands for arret refroidissement (stop cooling)

Intro to Austenite 上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY In Fe-C system:austenite solid solution of C in fcc Fe Interstices in FCC structure. (a)Octahedral void. (b)Tetrahedral void. (a) (b) ●.Regular site atoms K.Chen 8

K. Chen Intro to Austenite 8 In Fe-C system: austenite solid solution of C in fcc Fe Interstices in FCC structure. (a)Octahedral void. (b)Tetrahedral void. >

Intro to Austenite 上游充通大粤 SHANGHAI JIAO TONG UNIVERSITY In Fe-C system:austenite solid solution of C in fcc Fe All octahedral interstices occupied? →50at%C,or,20wt%C →Maximum2.11wt%C →Therefore,No！ →The maximum is10at%C 0.364 0.362 wu/ Fe 0.360 Because: 1A0 Radius of C is 0.77A 0.358 >Radius of octahedral site is 0.52A >Lattice distortion>100%occupied 0.356 impossible Lattice parameter 0 0.5 1.0 1.5 2.0 increase C Concentration / K.Chen 9

K. Chen Intro to Austenite 9 In Fe-C system: austenite solid solution of C in fcc Fe All octahedral interstices occupied?  50 at% C, or, 20 wt% C  Maximum 2.11 wt% C  Therefore, NO!  The maximum is 10 at% C Because:  Radius of C is 0.77Å  Radius of octahedral site is 0.52Å  Lattice distortion  100% occupied impossible  Lattice parameter increase C Concentration /% Austenite Lattice Parameter /nm

Intro to Austenite h 上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Properties: Stabilizable to produce Austenitic Steel FCC>low hardness and yield strength ©FCC→good formability FCC>most closely packed>Smallest specific volume Small self-diffusion coefficient of Fe>high-temperature application ©Paramagnetic→non-magnetic steel Large liner expansion coefficient Poor thermal conductivity>heating/cooling rate? AI JIAO TONG UNI K.Chen 10

K. Chen Intro to Austenite 10 Properties: Stabilizable to produce Austenitic Steel FCC  low hardness and yield strength FCC  good formability FCC  most closely packed  Smallest specific volume Small self-diffusion coefficient of Fe  high-temperature application Paramagnetic  non-magnetic steel Large liner expansion coefficient Poor thermal conductivity  heating/cooling rate?