以作者前期提出的位错塞积模型为基础, 结合断裂强度与晶粒尺寸的关系, 建立了晶粒细化导致超细晶粒钢总伸长率降低的临界晶粒尺寸的计算模型. 以晶粒尺寸从10 mm减小到0.2 mm为例, 计算结果表明, 钢的总塑性伸长率随着晶粒尺寸的减小首先呈现增加的趋势, 但是当晶粒尺寸减小到大约2.5 mm后, 随着晶粒尺寸的减小, 钢的总伸长率不仅不再增加, 反而出现了显著的降低, 这一结果较好地吻合了近期超细晶粒材料研究的实验现象. 本工作的研究说明, 导致超细晶粒钢伸长率降低的主要机制在于当晶粒细化到一定程度后, 晶界对位错源开动的阻力增大, 由此导致的可动位错数目显著降低使得应变量显著减少.

Based on our earlier preliminary work, a model was developed for prediction of the critical grain size where the plasticity would be decreased as the grain refined. In the model the effect of grain size on the fracture strength was combined. The prediction of the model exhibited that in the range of grain size of 10 mm to 0.2 mm as an example, the total elongation of the steels would be firstly increased. But when the grain size was refined to 2.5 mm and below, the total elongation of the steels was not increased but decreased sharply, which was good agreement with the experimental results published recently. Present work illustrated that the dominant mechanism of the elongation decreased in the ultra-fine grain size materials is due to increase in resistance force of grain boundaries on the dislocation sources resulting in the difficulty of activation of dislocation movements. Its expression would be the decrease of the plastic strain in macro-level.