核压力容器用钢高温大变形所致织构大晶粒的形成条件与演化机理

因大变形而产生明显织构倾向的晶粒长时间处于高温环境易发生合并形成织构大晶粒，引起材料性能各向异性，严重降低锻件的塑性、韧性和疲劳性能。织构大晶粒的形成与初始晶粒状态、变形过程中的应变分布和再结晶形核与长大的择优取向等因素有关，然而仅通过实验观测很难揭示其形成条件与演化机理，目前尚缺乏有效的研究手段。本项目以厘清核岛大锻件锻造过程织构大晶粒的形成条件和演化机理为目的，采用微观组织表征、锻造工艺实验和多尺度模拟相结合的方法，以非连续热变形过程位错密度与织构演变为线索，结合分子动力学计算表征与晶界特征相关的择优取向并转化为织构模拟中的取向转变规则，建立考虑各向异性晶粒三维晶体学信息的多级元胞模型，揭示织构大晶粒形成条件与演化机理，提出避免出现织构大晶粒的极限参数范围确定方法。通过对上述问题的深入研究和解决，形成一套行之有效的晶粒与织构演化计算方法，为核岛大锻件织构大晶粒的预控提供理论分析依据。

The grains with obvious texture tendency are easy to merge into textured large grains because of the large deformation and following with long holding time at high temperature. Textured large grains have strong impact on the anisotropy of the materials. And they can severely reduce the plasticity, toughness and fatigue properties of forgings. The formation of textured large grains is due to the comprehensive effect of the initial grain, the distribution of the strain during deformation and the preferred orientation during nucleation and growth of the newly recrystallized grains. However, it is difficult to reveal the formation and evolution mechanism only using experimental observation. At present, there is also a lack of effective calculation method. The project aims to investigate the refinement condition and evolution mechanism of the textured large grains during heavy forging process for nuclear island, though experimental observation, forging process and multiscale simulation, taking the evolution of the dislocation density and the texture as the main line, combining the characterization of grain boundary with the preferred orientation by using molecular dynamics and building the transformation rules, and establishing the multi-level mesoscale model, to reveal the formation condition and evolution mechanisms of the textured large grains. The research of this project will form an effective computational method for the prediction of grain and texture evolution, and the achievement will provide theoretical basis for the control of heavy forging for nuclear island.