第五章钢的退火选编.ppt

第五章 钢的退火与正火;5．1 Annealing of steel 5.1.1 Transformation during heating;1. Formation process of Austenite;Nucleation of A ;Growth of A nucleus/grains;Solution of remained CM, homogenization of A;注意：以上形成模式只适合加热速度不太高的情况，对于高速加热的早期阶段，钢中奥氏体转变以位移型转变—贝氏体型转变为主, Referred to W.J. Kaluba et al., Acta Mater.,46(1998),5917-27;(At high heating rate!);At early stage for high heating rate: Step 1: Superheating cause local supersaturate of carbon and diffusion along grain boundary of ferrite. Step 2: Lath formation of A Step 3: Coalescence of the A lath;Microstructural features: (1) Lath-like products at early stage of formation; (2) Direct formation at ferrite grain boundaries; (3) Kurdjumov-Sachs orientation relationship with the parent grain of ferrite; (K-S) (4) Lateral growth of the sheaves of austenite by side-by side coalescence.;2. Kinetics for A formation at Isothemal condition;Factors affecting the formation rate of A; 3．Grain size of A ; 影响奥氏体晶粒长大及最终晶粒大小的因素 ;铁轨用弹簧钢60Si2MnA: Fe-0.6C-1.74Si-0.7Mn-0.011P-0.006S-0.12Cr, Treated at different T for 1.5hr.;（2）A的实际晶粒度;5.1.2 Transformations during cooling of steel;Transformation products of undercooled A: ;;2. Factors influencing the “C” curve ;Effect of carbon content on “C” curve;过/亚共析钢的”C”曲线;Effect of alloying elements;3．CCT map of A: practical, welding ;4．Critical cooling rate: Here for steel in continuous cooling，no pre-eutecoid F or CM forming. Higher rate of cooling: the minimal cooling rate in order to obtain overall M microstructure ----Critical quenching Lower rate of cooling: the maximum cooling rate to obtain overall P microstructure; 5．Applications of TTT or CCT ;应用： 冷却曲线与C曲线重叠 找相交点，估计产物 与实际有差异 For example: Cooling curve b: (P)+M+(A)rem. Cooling curve d: (P);5.1.3 Formation of Pearlite in steel during eutectoid transformation ;Schematic process for pearlite formation;奥氏体分别与渗碳体和铁素体平衡，但由于在P或CM的端向含C量差异，在珠光体前沿出现浓度梯度。;珠光体端向长大（续）;2． Relationship of crystallographic orientation