SDP2新型贝氏体模具钢的相变及动力学

Transformation process and kinetics in a new plastic mould of bainite steel SDP2

对新开发大截面贝氏体塑料模具钢SDP2在极低冷速下的过冷奥氏体连续冷却转变过程和相变动力学进行了研究。采用DIL805A高精度差分热膨胀仪测量SDP2钢线膨胀行为,利用SEM分析冷却转变产物;根据JMA公式计算SDP2钢贝氏体相变激活能和Avrami指数。结果表明,SDP2钢过冷奥氏体连续冷却过程包含珠光体、贝氏体和马氏体转变,而无铁素体转变;当冷速大于0.02℃/s时,转变产物以下贝氏体或马氏体为主;小于0.02℃/s时,以上贝氏体或粒状贝氏体为主,并出现珠光体。SDP2钢贝氏体转变的激活能为117 k J/mol,SDP2钢在不同冷速下贝氏体转变动力学指数Avrami指数n≈2~3,经分析计算所得的Avrami指数值所对应的显微组织形态和实验所观察到的显微组织相符合。

The continuous cooling of undercooBng austenite transformation process and the transformation kinetics for a new large section bainite plastic die steel SDP2 cooling at ultra-low rates were investigated. The expansion curves of SDP2 steel were measured by using DILS05A dilatometer. The transformation products were analyzed by SEM. Finally, the activation energy and Avrami exponent of the bainite transformation for steel SDP2 were calculate by JMA equation. The results show that the transformation product of undercooled austenite includes pearlite, bainite and martensite in SDP2 steel under continuous cooling conditions. When the cooling rate is more than 0.02 ℃/s, the microstructure of the SDP2 steel mainly contains upper bainite and granular bainite, and begin to appear pearlite, otherwise, the microstructure of the SDP2 steel mainly consists of a mixture of lower bainite and lath martensite. Activation energy and Avrami exponent （n） of bainite transformation is 117 kJ/mol and about 2-3 under different cooling rates. The microstructure draw from Avrami exponent is in accord with the experimental results.