Nb-V-Ti超高强度钢碳化物转变机制及其组织控制

Development of ultra-high strength steels is the key to the localization and re-export of advanced equipments, and both their safety and service life are closely related to the strength and toughness of steels. To improve the strength and toughness of ultra-high strength steels, it is essential to tailor the microstructure and optimize the complex structure between the matrix and carbides. In this project, based on the previous studies on Nb-V-Ti ultra-high strength steel, microstructure evolution and mechanical performances of the Nb-V-Ti microalloyed ultra-high strength steel subjected to heat treatments will be investigated by SEM, TEM, XRD examination and mechanical tests.The combined strengthening effects between martensite and thermally stable carbides will be used to ensure the excellent strength and toughness of steels, and the microstructure will be further tailored and optimized. The matrix design will be focused on significant effects of microstructure refinement on strength and toughness of steels, while the carbide design will be focused on the effects of tempering treatment and magnetic field on types, morphologies, distribution and evolution of carbides. The optimal microstructure will be identified by processing optimization, and the relationship between the microstructure and mechanical performance will be clarified, as well as the strengthening mechanisms, which will provide fundamental knowledge and guidance for the microstructural control and performance optimization of ultra-high strength steels.

超高强度钢开发是实现高端装备国产化及再出口的关键，其强韧性决定着高端装备的安全性及使用寿命，迫切需要开展基于强韧性提高的组织设计、基体与碳化物强化相复合结构调控等方面的工作。在此背景下，本项目拟在前期Nb-V-Ti超高强度钢研发基础上，采用SEM、TEM、XRD以及力学性能测量等手段，对25CrMo48V钢的组织、碳化物及性能的演变规律进行系统分析。探索马氏体基体高热稳定弥散碳化物的引入确保超高强度钢优异强韧性能的新途径，进一步优化超高强度钢的微观组织。其中基体组织设计将重点考虑马氏体板条细化对强韧性提高的关键作用，强化相将重点关注回火处理和磁场热处理对碳化物种类、形态、分布以及演变规律的影响，通过工艺参数优化来确定其理想微观组织，阐明微观组织和力学性能之间的内在关联性，澄清其强韧化机制，为超高强度钢的组织调控及性能优化提供基础数据和指导。

超高强度钢广泛应用于航天航空、高速铁路和新能源开发等领域。高端装备国产化对我国自主生产的超高强度钢强韧性能提出更高要求，迫切需要开展基于强韧性提高的组织设计、基体与碳化物强化相复合结构调控等方面的工作。本项目系统研究高温回火条件下不同回火时间、磁场条件下回火温度及回火时间对25CrMo48V超高强度钢显微组织及性能的影响。结合高温回火时间条件下组织、碳化物及性能之间的内在联系。明确25CrMo48V超高强度钢代表性显微组织为板条马氏体基体及板条间少量残余奥氏体，基体内部有六种不同类型尺寸碳化物析出，阐明600oC高温回火时不同种类碳化物演变规律为M3C→M2C→M7C3→M23C6；通过磁场热处理对组织及碳化物演变规律影响的分析，澄清磁场施加会抑制马氏体板条合并，促进M23C6与M7C3型碳化物提前析出，阐明磁场热处理在控制碳化物种类、形貌、尺寸及分布方面所起到的作用，为磁场热处理提高材料强韧性提供基础实验数据和理论指导。本项目的顺利实施有助于加深热处理工艺对超高强度钢组织、碳化物演变及性能影响的理论认知，从显微组织的角度探索超高强度钢强韧化机制，为超高强度钢的制备和加工提供理论依据。