形变对Cr-Mo低合金钢相变的影响

 Cr-Mo低合金钢在工业生产中有着重要的应用。CCT曲线是研究过冷奥氏体相转变的重要依据。通过Gleeble-3500热模拟试验机及DIL805A淬火变形膨胀仪模拟了Cr-Mo低合金钢的变形及冷却工艺，并利用超组元模型进行热力学计算分析。理论计算结果表明，形变通过提高了Cr-Mo低合金钢相变过程中的自由能进而影响了碳在奥氏体中的活度及相界面碳平衡摩尔分数，相界面碳平衡摩尔分数的变化带来了相变驱动力与形核驱动力的不同，进而影响相变的孕育期与过冷度。结果表明，相变孕育期与过冷度的变化与理论计算结果一致，热力学计算很好地解释了形变对相变的影响。同时表明形变可以提高铁素体相变临界冷速，当冷速为0.3 ℃/s时，Cr-Mo低合金钢可获得最为均匀细小的铁素体晶粒。适当的变形与冷却工艺对改善Cr-Mo低合金钢组织与性能有着重要的作用。

Effect of deformation on the phase transformation of Cr-Mo low alloy steel

Cr-Mo low alloy steel has important applications in industrial production. CCT curve is an important basis for the research on the phase transformation of supercooled austenite. The deformation and cooling process were simulated by Gleeble-3500 thermal simulation tester and DIL 805 dilatometer in this paper. The superelement model was used to do the thermodynamic calculation and analysis. The results indicate that the deformation has a great influence on the phase transition free energy of Cr-Mo low alloy steel during the process of transformation， also on activity of carbon， mole fraction of carbon on phase boundaries， driving force of transformation and driving force of nucleation， which has an effect on the the incubation period and the degree of supercooling of the transition in the end. The measured results show that the incubation period and the degree of supercooling consistent with the theoretical calculated results. The deformation can also be used to enhance the critical cooling rate ferrite transformation. The finest ferrite grain can be obtained when the cooling rate is 0.3 ℃/s. Therefore， appropriate deformation and cooling process is of great importance in improving the microstructure and properties of Cr-Mo low alloy steel.