Q&P工艺参数对34SiMn2CrNiMo钢组织和力学性能的影响

Effects of Q&P technological parameters on microstructures and mechanical properties of 34SiMn2CrNiMo steel

设计制备一种中碳合金钢34SiMn2CrNiMo,通过对淬火-配分(Q&P)热处理试样的显微组织表征和力学性能测试,建立工艺-组织-性能的关系,结合热膨胀相变行为研究结果,探讨淬火中止温度TQ、加热模式、配分温度TP和配分时间tP对组织演变的影响规律并进行强韧性机理分析。结果表明:实验钢经过Q&P处理后可以获得马氏体+残余奥氏体的复相组织,从而大幅提高强塑性。在最佳处理状态组织中残余奥氏体体积分数约为24%,屈服强度为1053 MPa,抗拉强度为1607 MPa,伸长率为24.9%,强塑积为40.0 GPa·%。为了避免生成块状二次马氏体,实验钢最佳淬火温度应位于马氏体相变开始温度Ms以下150℃左右。实验钢不完全淬火后缓慢加热比快速加热配分能获得更多的残余奥氏体,钢的塑韧性提高更明显。实验钢在400℃配分时Q&P组织和性能相对稳定,而在450℃配分时残余奥氏体体积分数随时间延长而减少,导致屈服强度和伸长率同步下降。

A medium carbon steel 34SiMn2CrNiMo was designed and fabricated,and the relationships between processing,microstructures and mechanical properties were established through microstructure characterization and mechanical properties testing on the quenching and partitioning(Q&P)heat-treated samples.Based on the experiment results of thermal expansion transformation behavior,the effects of quenching temperature TQ,heating approach,partitioning temperature TPand partitioning time tPon microstructures evolution were investigated and mechanism of strength and toughness was illuminated as well.The results show that multiphase microstructures of martensite and retained austenite can be obtained by means of Q&P processing,as a result the match of strength and plasticity is greatly improved.In the optimal treatment state,the retained austenite volume fraction is about 24%,the yield strength is 1053 MPa,the tensile strength is 1607 MPa,the elongation is 24.9%,and the product of strength and elongation(PSE)is 40.0 GPa·%.To avoid forming the blocky secondary martensite,the best quenching temperature has to be set at least 150℃below martensitic transformation starting temperature Ms.More retained austenite can be achieved by slow heating than fast heating upon partitioning after the steel is incompletely quenched,the plasticity and toughness are improved apparently.The microstructures and properties of Q&P treated steel keep relatively stable with prolonged duration when it is partitioned at 400℃.However,the volume fraction of retained austenite decreases with tPat 450℃,leading the yield strength and elongation decrease simultaneously.