超高强度纳米钢兼具高强度、高塑性和优异的耐腐蚀性与焊接性能，具有广阔的应用前景。已有的研究表明，纳米相结构对钢的力学性能有直接和重要的影响。具有复杂结构的多相同位共沉淀纳米相较单一纳米相具有更高的热稳定性和更显著的强韧化效果，而纳米相结构及其热稳定性又与钢的成分与热加工工艺密切相关。本项目提出富铜纳米团簇与纳米碳化物、纳米金属间化合物三者同位共沉淀形成复杂结构纳米相强化低碳低合金钢的新思路，利用HRTEM、3D-APT和SANS从局部原子尺度和统计分析相结合的方法对纳米相结构和成分分布进行表征，系统研究合金成分与时效处理对同位共沉淀复杂纳米相结构和异相界面结构状态的影响，探明纳米相形成、演化规律及其影响因素，深入理解复杂结构纳米相形核长大热、动力学机制，揭示纳米析出强化钢的强、韧化机理，为有效控制纳米相结构、进一步提高钢的综合性能、设计新型超高强度钢提供理论指导。

Ferritic steels strengthened by nano-scale precipitates have outstanding mechanical and metallurgical properties, including high strength and toughness, good corrosion resistance and desirable weldability. Thus, these steels have a great potential for structural use in advanced engineering systems and energy conversion power plants. The superior properties are derived from the co-precipitation of multiple particles of nano-clusters, nano-intermetallic phases and nano-carbides. The complex nano-particles produced by both alloy-composition control and thermo-mechanical treatment possess superior thermal stability and prominent hardening effects as compared with those single nano-precipitates.The objective of this proposal is to understand the basic mechanisms controlling the complex precipitation processes of the three nano-particles as well as the strengthening mechanisms of the nano-precipitates. Furthermore, our efforts will be focused on the enhancement of the stability of coherent interphase boundaries via control of boundary energy and chemistry. In order to achieve these goals, analytical tools of high-resolution transmission electron microscope (HRTEM), 3-dimenstional atom probe tomography (3D-APT) and small-angle neutron scattering (SANS) will be utilized to characterize microstructural features of these clusters and particles at the nanoscale. Also, computer-aided calculations based on Thermo-Calc and JMatPro software will be applied to determine the transformation kinetics, grain size, and phase formation in multicomponent ferritic steels. All these efforts will lead to the design of a new class of ultra-high strength steels with superior mechanical properties for structural applications.