新型孪生诱发塑性淬火-分配-回火钢微观组织和力学性能研究

A new generation of advanced high strength steels emphasizes the precise control of the microstructure in order to improve the strength at the same time not lowering the plasticity even improving it. Recently, quenching-partitioning (Q-P) process and quenching-partitioning-tempering attract extensive attention, which can make material with high strength and good plasticity by precisely controlling the retained austensite content and optimizing the morphology of steels. Based on the enhanced ductility mechanism by austensite in Q-P-T steels, recently, we proposed the dislocation absorption by retained austensite (DARA) effect which happens in uniform deformation by the dislocations transporting from martensite to austensite at their interfaces. However, the specific micromechanism still needs further research and development. This project will be researched on the relationship between the mechanical and the microstructure of high carbon and medium manganese Q-P-T steels by designing different aluminum contents in these steels. Thus, this project can verify the enhanced ductility mechanism of DARA effect in Q-P-T steels. Thus, combined with Twinning Induced Plasticity (TWIP) and Tranformation Induced Plasticity (TRIP), the strength and plasticity of these steels can be further enhanced. In conclusion, this work will lay a solid foundation for designing a new generation of advanced high strength steels.

新一代先进高强钢（AHSS）强调微观组织的精确调控，在提高强度的同时不损害甚至提高塑性。最近提出的淬火-分配（Q&P）和淬火-分配-回火（Q-P-T）工艺可以通过精确控制残余奥氏体分数并优化组织形态，使材料兼具高强度和良好塑性，受到广泛关注。针对Q-P-T钢残余奥氏体增强塑性机制，申请人最近提出在均匀形变阶段位错越过马氏体/奥氏体界面的残余奥氏体吸收位错（DARA）效应，但具体的微观机制仍需进一步研究和拓展。本项目拟通过设计具有孪生诱发塑性（TWIP）效应的高碳Q-P-T钢，研究力学性能与微观组织之间的关系，进一步验证高碳Q-P-T钢中的DARA效应增塑机制，并结合TWIP效应和相变诱发塑性（TRIP）效应进一步提高钢的强度和塑性，为新一代高强高塑AHSS的组织设计奠定理论基础。

设计了具有少量孪生诱发塑性（TWIP）效应的高碳Q-P-T 钢，研究力学性能与微观组织之间的关系，验证了高碳Q-P-T 钢中存在DARA 效应增塑机制。在Q-P-T 钢形变过程中，残余奥氏体具有三个相继的效应，即DARA效应、TRIP效应和BCP效应，三者共同构成残余奥氏体增强高强度钢塑性的微观机制。三种效应均相继增强了硬相马氏体与邻近残余奥氏体软相协调形变的能力，继而相继提高了高强度钢的塑性。.另外，对比相同碳含量（0.2 wt.%）的三种材料分别通过Q&P和Q-P-T工艺处理并充氢后的慢应变速率拉伸（SSRT）力学性能，发现微合金元素Nb通过细晶强化和弥散强化进一步提高Q-P-T钢的强度，不同形态粗大的和细小弥散分布NbC颗粒作为氢陷阱捕获大量的氢，增强Q-P-T钢的抗氢脆敏感性；奥氏体的形状和位置对氢的捕获能力有区别，马氏体条间的残余奥氏体捕获能力更强；同样为软相的铁素体并没有表现出较强的捕获氢的能力。