The conventional micromechanical approaches today are still not able to properly predict the ductile-to-brittle transition (DBT) of steels because of their inability to consider the co-operating ductile fracture and cleavage mechanisms in the transition region, and simultaneously to incorporate the inherent complexity of microstructures. In this study, a complete methodology with coupled cellular automata finite element method (CAFE) and multi-barrier microcrack propagation models is presented to advance the prediction of DBT. The methodology contains three key elements: (i) a multiscale CAFE modelling approach to realize the competition between ductile damage and cleavage fracture and embrace the probabilistic nature of microstructures, (ii) a continuum approach to estimate the effective surface energy for a microcrack to penetrate over particle/matrix interface, and (iii) a method to calculate the effective surface energy for the microcrack to propagate across grain boundaries. The prediction of DBT therefore needs only (1) the stress-strain curves tested at different temperatures, (2) the activation energy for DBT, (3) the ratio between the size of cleavage facets and cleavage-initiating defects, and (4) key statistical distributions of the given microstructures. The proposed methodology can accurately reproduce the experimental DBT curve of a low-carbon ultrahigh-strength steel.

如今，传统的微机械方法仍无法正确预测钢的延性-脆性转变（DBT），因为它们无法考虑过渡区域中的协同延性断裂和分裂机制，同时无法整合固有的微观结构的复杂性。在这项研究中，结合细胞自动机有限元方法（CAFE）和多屏障微裂纹传播模型的完整方法被提出，以推进DBT的预测。该方法学包含三个关键要素：（i）多尺度CAFE建模方法，以实现延性损伤与乳沟断裂之间的竞争并包含微观结构的概率性质，（ii）估算微裂纹穿透颗粒/基质界面的有效表面能的连续方法，以及（iii）计算微裂纹跨晶界传播的有效表面能的方法。因此，对DBT的预测仅需要（1）在不同温度下测试的应力-应变曲线；（2）DBT的活化能；（3）分裂面的大小与分裂引发缺陷之间的比率；以及（4）给定微结构的关键统计分布。所提出的方法可以准确地再现低碳超高强度钢的实验DBT曲线。因此，对DBT的预测仅需要（1）在不同温度下测试的应力-应变曲线；（2）DBT的活化能；（3）分裂面的大小与分裂引发缺陷之间的比率；以及（4）给定微结构的关键统计分布。所提出的方法可以准确地再现低碳超高强度钢的实验DBT曲线。因此，对DBT的预测仅需要（1）在不同温度下测试的应力-应变曲线；（2）DBT的活化能；（3）分裂面的大小与分裂引发缺陷之间的比率；以及（4）给定微结构的关键统计分布。所提出的方法可以准确地再现低碳超高强度钢的实验DBT曲线。