Q&P处理中碳富硅高强钢分配过程亚稳奥氏体转变动力学及组织演变机制研究

Quenching and Partitioning (Q&P) process treated steels have been considered as the third generation advanced high strength steels, because it has the characteristics of low coast, high strength, good plasticity and toughness. In the past few years, some encouraging progress has been made in theoretical studies of the process. It has been defined the carbon diffusion behavior during the partitioning process and the relationship between Q&P process and mechanical properties. However, some issues need further research such as the changing behavior of metastable austenite during the partitioning process. Additionally, less attention are paid on the Q&P process for traditional medium carbon Si-rich steels to enhance their mechanical properties..In this project, commercial medium carbon Si-rich high strength steel (60Si2CrVA) will be in-situ researched by 805A/D dilatometer during the Q&P process. We will study the changing behavior of metastable austenite during the partitioning process. Reveal metastable austenite transformation mechanisms, build up the transformation dynamic model of metastable austenite, get the influence of short time isothermal quenching process parameters on the initial microstructure and obtain the microstructure evolution dependence on initial microstructure during the partitioning process. Propose the scientific principle of controlling initial microstructure difference affecting on the microstructure changing behavior during the partitioning process. The microstructure and mechanical properties can be controlled accurately for medium carbon Si-rich high strength steels treated by Q&P process. Promote the industrial application of Q&P process in medium carbon Si-rich high strength steels.

Q&P钢因其具有低成本和高强塑韧性配合的特征，被认为是发展第三代超高强度钢的主要手段。近年来,该工艺在基础理论上取得了明显进展。明确了分配过程的碳扩散行为和工艺与力学性能之间的关系，但是关于分配过程中亚稳奥氏体的转变行为等问题有待进一步深入研究，同时，对于传统中碳富硅钢的Q&P热处理强韧化机理研究匮乏。.本项目以商用中碳富硅高强钢（60Si2CrVA）为研究对象，采用高温相变仪（DIL 805A/D）在线研究Q&P处理时，分配过程中亚稳奥氏体的转变行为，明晰亚稳奥氏体的演变机制，建立亚稳奥氏体转变的动力学模型；探明短时等温淬火工艺参数对初始组织的影响，明确分配过程组织转变对初始组织的依赖关系,提出控制初始组织差异对分配过程组织转变行为影响的科学原则，准确调控中碳富硅高强钢经Q&P处理后的显微组织和力学性能，促进Q&P工艺在中碳富硅高强钢中的工业应用。

Q&P钢因其具有低成本和高强韧性配合的特征，被认为是发展第三代超高强度钢的主要手段。近年来,围绕该工艺的研究在基础理论上取得了明显进展。明确了分配过程的碳扩散行为和工艺与力学性能之间的关系，但是关于分配过程中亚稳奥氏体的转变动力学和显微组织演变机制等问题有待进一步深入研究，同时，对于传统中碳富硅钢的Q&P热处理强韧化机理研究匮乏。为了解决上述问题，本项目以商用中碳富硅高强钢（60Si2CrVA）为研究对象，采用相变仪（DIL 805A/D）、TEM、SEM、XRD、MTS材料试验机等研究手段，系统研究了试验钢连续冷却转变过程中的相变行为，Q&P工艺参数对组织性能的影响以及亚稳奥氏体分配过程中的转变行为。绘制了60Si2CrVA 钢的CCT曲线，掌握了亚稳奥氏体在分配过程中的组织演变机制，建立了亚稳奥氏体在分配过程中的转变动力学模型；明确了等温淬火工艺参数对一次马氏体、亚稳奥氏体含量、形态和分布的影响；建立了一次淬火组织对分配过程亚稳奥氏体、马氏体、贝氏体以及碳化物转变的影响规律，获得了初始组织对最终组织的影响关系，提出了通过控制一次淬火工艺来控制初始组织的科学原则，进一步丰富了Q&P处理中碳富硅高强钢的强化理论，成功实现对中碳富硅高强钢经Q&P工艺处理后的显微组织和力学性能的准确调控；为Q&P工艺在中碳富硅高强钢产品上的推广应用奠定了良好的理论基础。