高强度高韧性是钢铁材料的主要发展方向。如何使钢铁材料兼备超高强度和良好的韧性是研究热点。本项目针对“高强度纳米结构金属材料的加工硬化能力低”这一科学问题，制备具有不同晶粒尺寸、析出相尺寸与分布的纳米晶粒结构D6A钢，研究纳米结构材料在复杂应力下的晶粒转动、再结晶等现象的成因及其与力学性能变化的关系；揭示晶粒尺寸、晶粒取向、析出相尺寸与分布、微应力分布等对纳米晶粒结构D6A钢加工硬化能力的影响规律；探索在复杂应力作用下，纳米晶粒结构材料微区多尺度应力分布变化引起的微观结构退化及纳/微裂纹起源、演化规律；提出有效改善纳米晶粒结构D6A钢的塑性的技术措施。本课题的研究，为开发高强、超塑、成型性能更优的D6A钢提供实验和理论支撑，丰富金属材料在纳米尺度下的变形理论，具有重要学术价值。同时，为工程材料的使役性能预估提供实验及理论借鉴，对航空航天、军工、工程应用等领域中关键材料的需求等都具有重要意义。

The main target of steel development is how to achieve both the higher strength and better toughness simultaneously. Currently, much attentions have been focused on how to maintain the good ductility as increasing strength. Based on the scientific issuse of poor work-hardening ability of nanostructured metals with a high strength, four parameters including grain size, grain misorientation, precipitations size and distributions have been suggested as the dominated factors. The main objective of this project faces to explore relationship between mechanical properties and the grain misorientation, grain rotation, recrystallization as well as lattice distortion of the D6A alloys with various nanoscale grain sizes and precipitation types and sizes under a complex stresses, based on the direct measurements of lattice strain distributions by in-situ neutron scattering and synchrotron-based X-ray diffraction experiments, in combination with other advanced in-situ characterization as well as post-mortem TEM observations.. The fundamental mechanisms responsible for the degeneration of microstructures and the origin and evolution of nano-/micro-scale cracks/voids of nanocrystalline D6A alloys will be elucidated by exploring the evolution of work-hardening ability with the variation of grain size and grain misorientation, characteristics of typical grain boundaries, micro-stress distribution, volume fraction and distribution of precipitation. The mechanisms are closely related to the evolution of microstructural unit including grain size and precipitations distribution, resulting from the variation of micro-stress/strain distribution under complex deformation conditions.. It is predicted that some breakthroughs will be achieved through a successful execution of this program in the following several aspects: (1) an effective measure will be suggested for improving the toughness of nanocrystalline D6A steel; (2) a significantly experimental and theoretical basis will be provided for the devolepment of a new generation of D6A steels possessing the higher strength, better ductility, and enhanced formability; (3) the deformation theories of metallic materials with nanoscale microstructures will be enriched；(4) a new microstructure-based damage theory will be developed to predict accurately the service performance and deformation damage of anisotropic nanocrystalline materials under the complex service conditions. This is extremely important for the demands of key materials in the fields of aerospace, military industry, and engineering application.