非均匀层状双相不锈钢强韧化机理的原位电镜定量研究

As a new microstructure design strategy, heterogeneous lamella structure (HL) in a single phase material has shown an excellent combination of high strength and high ductility due to the improved work hardening rate. However, there is no such report on two phase materials. A preliminary experimental investigation has been tried to produce an HL two phase structure in a commercial SAF 2507 duplex stainless steels. The strength of the steel has been improved to be about 1GPa and the elongation is around 30%, greater than its coarse grained counterpart. Based on this result, we intend to systematically investigate the stability of the lamella structure during heat treatment and the strengthening mechanism during deformation, focusing on the generation and multiplication of dislocations, interactions of dislocations with dislocations and grain boundaries, the interactions of micro-cracks with dislocations and grain boundaries, as well as the effects of above phenomena on the flow stress. By using various in situ techniques, such as tensile test in SEM, in situ tensile and compression tests in TEM and in situ heating test in TEM, an improved understanding of the characteristic strengthening and toughening mechanisms in heterogeneous lamella two phase steels can be expected. This will provide guidelines for the design of advanced steels with high strength, ductility and toughness.

作为一种新的组织结构设计思路，非均匀层状结构在单相材料中获得了高于粗晶材料的加工硬化率及强塑性匹配。申请人将这一结构设计思路拓展到双相材料中，在试制的商用SAF2507双相不锈钢中得到了令人鼓舞的初步成果，拉伸强度约1GPa时延伸率仍能达到30%左右。然而，为了实现对非均匀层状双相结构特性的调控和力学性能的优化，需要针对材料原始组织、变形及热处理工艺对层状结构演变的影响、热处理过程中层状结构的稳定性、各层变形过程中的微观机理和协调机制，及其对裂纹扩展的影响等开展系统的研究。本项目针对以上情况，将以SAF2507双相不锈钢为主要研究材料，利用SEM中原位拉伸实验，TEM中原位加载及加热实验，研究非均匀层状结构钢强韧化的微观机理及热处理过程中层状结构的稳定性，这些研究成果将丰富结构钢的强韧化基础理论，并为设计新型高强度高韧性结构钢提供新的指导方针。

作为一种新的组织结构设计思路，非均匀层状结构在单相材料中获得了良好的强塑性匹配。申请人将这一结构设计思路拓展到双相材料中，在商用铁素体-奥氏体双相不锈钢及中锰铁素体-马氏体双相钢中通过热锻/冷锻、热轧或冷轧加退火工艺等方式，制备出了非均匀层状双相结构。利用扫描电镜、透射电镜、电镜内的原位力学表征、纳米压痕及宏观/微观DIC等方式，研究了材料原始组织、变形及热处理工艺对层状结构演变的影响、热处理过程中层状结构的稳定性、各层变形过程中的微观机理和协调机制等；系统考察了微观组织结构对材料力学性能的影响，通过在微纳尺度考察强韧化机制为先进高强金属的微观组织设计与力学性能优化提供有效的实验依据及理论指导，从而实现对非均匀层状双相结构特性的调控和力学性能的优化。项目执行期间，发表论文11篇，其中包含1篇Scripta Mater.，4篇Mater. Sci. Eng. A，两篇J Mater. Eng. Performance及3篇国际会议论文。申请发明专利2项，其中，授权1项。