低温动载荷下富锰残余奥氏体的变形行为及韧化机理

In this project, the low carbon and medium manganese design is proposed to introduce retained austenite acting as another toughening mode in hot rolled heavy steel plate, and the objective is to systematically resolve the practical problem that the low temperature toughness of high strength heavy steel plate greatly decreases as the strength and thickness increase and the limitation of conventional toughening mode. The key problems consisting of the deformation behavior of Mn-rich retained austenite under dynamic loading and low temperature conditions and the mechanism of its effect on crack initiation and propagation are systematically investigated. The methods to obtain retained austenite with different characteristics are made clear. The intrinsic control factors affecting the stability of retained austenite are determined. Moreover, the quantitative models of the volume fraction, stability and stacking fault energy of retained austenite are also established. The size and volume fraction of nano-cell structure, twins, ε martensite and α′ martensite and the nucleation and growth mechanism are emphatically analyzed. The deformation behavior of Mn-rich retained austenite under the dynamic loading and low-temperature conditions and its key affecting factors are determined. The role of deformation behavior of retained austenite under the dynamic loading and low-temperature conditions in enhancing plasticity of matrix and crack initiation and propagation is clarified. This work will be expected to reveal the toughening mechanism of Mn-rich retained austenite under the dynamic loading and low-temperature conditions. Moreover, the theoretical and experimental data is provided to support the application of Mn-rich retained austenite in high strength heavy steel plate.

本项目针对高强中厚板低温韧性随着强度和厚度的增加而大幅下降的现实问题及传统韧化手段的局限性，拟采用低碳中锰设计在热轧中厚板中引入残余奥氏体作为另一种韧化方式，围绕低温动载荷下富锰残余奥氏体的变形行为及其对裂纹形核和扩展影响的微观机制等关键问题开展研究。弄清不同特征残余奥氏体的控制方法，确定残余奥氏体稳定性相关本征控制因子，建立残余奥氏体体积分数、稳定性和层错能的定量模型；重点分析残余奥氏体内的纳米晶胞结构、孪晶、ε和α′马氏体等的尺寸和体积分数及相关形核和长大机制，明确低温动载荷下富锰残余奥氏体的变形行为及其关键影响因子；阐明低温动载荷下残余奥氏体变形行为在改善基体塑性以及裂纹形核和扩展中的微观作用机制。本研究有望揭示低温动载荷下富锰残余奥氏体的韧化机理，为富锰残余奥氏体在高强中厚板中的应用提供理论和实验支撑。

高强度中厚板是支撑国家经济建设和社会发展的关键材料，但体心立方金属材料具有韧脆转变现象，使得高强度中厚板面临低温韧性差的技术难题。本项目拟采用低碳中锰设计引入残余奥氏体作为另一种韧化方式，围绕低温动载荷下富锰残余奥氏体不同的或新的变形行为及其对裂纹形核和扩展影响的微观机制等关键问题开展研究。并取得如下重要结果：1）发现残余奥氏体在准静态拉伸和动载荷冲击条件下不同的力学响应行为和不稳定残余奥氏体往往伴随更多的γ/ε、SF或TBs等界面缺陷，确定了残余奥氏体稳定性关键控制因素为形态、尺寸和化学成分；2）首次解释了残余奥氏体特性与强度、裂纹形核功和扩展功间的定量关系，发现残余奥氏体稳定性对裂纹形核功的影响相关较小，而其稳定性显著影响裂纹扩展功，明确了基体组织的回复在优化低温冲击韧性中的关键作用，揭示了残余奥氏体的韧化机理；3）残余奥氏体的变形行为与其稳定性密切相关，低温冲击变形后，板条残余奥氏体内存在一定量的薄片状ε马氏体，而块状γ/ε岛几乎全部转变为孪晶马氏体，孪晶马氏体的出现显著降低低温韧性。4）提出了采用抗拉强度和某一温度下冲击吸收功的乘积评价实验钢强韧性的方法，形成了高强度、高塑性和高韧性协同控制的方法，探索出一条新的进一步提升中厚板强韧性的技术路线。5）开发出690MPa级和1.0GPa级高强韧钢和可替代3.5Ni钢的低温钢，并具有在工程机械领域和低温领域应用的潜力。丰富了体心立方结构钢铁材料的韧化手段，并阐明了残余奥氏体的低温韧化机理，第一作者发表SCI论文5篇，获授权发明专利1项，培养研究生3名。