铁素体基Ti-Mo高强钢连续冷却相变及组织性能

摘要：为了深入了解铁素体基Ti-Mo高强钢在连续冷却相变过程中组织及硬度的变化及其原因，通过热膨胀法、金相及硬度等实验研究了Ti-Mo微合金钢在连续冷却条件下组织及性能的变化，探讨了冷却速率对组织、硬度及相变行为的影响机理，揭示了（Ti，Mo）C在奥氏体和铁素体中Ti/Mo原子比变化的原因。结果表明，随着冷却速率由0.06℃/s增加至17.9℃/s，组织依次为多边形铁素体+珠光体→多边形铁素体+粒状贝氏体→粒状贝氏体，硬度由144HV逐渐增大至228HV。当冷速由0.14℃/s增大至0.90℃/s时，组织中多边形铁素体比例不断增大，珠光体比例不断降低，硬度的提高主要来自于铁素体晶粒尺寸的细化及纳米级（Ti，Mo）C粒子的增多；当冷速由1.79℃/s增大至17.9℃/s时，组织中多边形铁素体比例不断降低，贝氏体比例不断提高，硬度的提高主要是由于贝氏体组织的细化及其比例的增加。（Ti，Mo）C粒子主要有2类：一类是奥氏体中析出的10～20nm的粒子，Ti原子数分数约为88%，另一类是铁素体中析出的小于10nm的粒子，Ti原子数分数约为68%，EDS测量结果与计算结果大致相当。

Microstructure and properties of continuous cooling transformation of Ti Mo ferritic high strength steel

In order to deeply understand the changes in microstructure and hardness of Ti-Mo ferritic high strength steel during continuous cooling transformation (CCT) process and the reasons，the microstructures and properties of Ti-Mo microalloyed steel during CCT process were investigated by the Formastor FП dilatometer method，hardness testing and metallographic experiments，and the mechanisms of the effect of cooling rates on microstructure，hardness，precipitation and the transformation behavior were analyzed. The reason of the changes of the Ti/Mo atomic ratios of（Ti，Mo）C was also revealed. The results show that the microstructures are successively evolving from polygonal ferrite + pearlite to polygonal ferrite + granular bainite and then to granular bainite，and the hardness increases gradually from 144 HV to 228 HV as the cooling rate increases from 0.06℃/s to 17.9℃/s. The percentage of polygonal ferrite is increasing while the proportion of pearlite is decreasing with the cooling rate increasing from 0.14℃/s to 0.90℃/s. The increase in hardness is attributed to the hardening of many nano-sized（Ti，Mo）C particles and the refinement of ferrite grain size. When the cooling rate further increases from 1.79℃/s to 17.9℃/s，the proportion of polygonal ferrite decreases，but the percentage of bainite increases continuously. The increase in hardness is mainly due to a larger proportion of bainite and the refinement of microstructure. There are two types of（Ti，Mo）C particles：one precipitates in the austenite with a size of 10~20nm and a Ti atom fraction of about 88%，and the other precipitates from ferrite with a size of less than 10nm and a Ti atomic fraction of around 68%. The calculated results are in approximate agreement with the measurements.