Brittle to Ductile Transition in Cleavage Fracture of Fe-3% Si Alloy

9906613氩多晶钢中晶界通过促进塑性松弛过程在抑制脆韧（B-D）转变温度方面的重要作用已得到充分证明。 然而，这种有益互动的实际形式并没有得到充分的理解。 在最近的基本实验和理论的考虑热引发的B-D转变的解理裂纹的传播，很明显，这种裂纹的晶界的重复机械逮捕促进塑性松弛，在抑制B-D转变温度有明显的有益效果。 因此，一个全面的研究计划，计划涉及的断裂阻力的实验测量的广泛选择的单个晶界在大双晶体的Fe-3%Si合金，收获从一个大的锭包含一系列的晶粒尺寸。 另外的实验研究检查了Fe-3%Si单晶中的热刺激B-D断裂转变，以清楚地了解控制转变的位错机制。 补充实验计划通过细晶粒多晶面板的解理断裂的拓扑特征。 这些测量的边界开裂阻力和其他注意到的方面的渗透的解理断裂通过一个领域的晶粒被纳入模型的全球解理开裂阻力。 该模型不仅适用于下陆架区，而且适用于上陆架区，在工程实践中具有直接的适用性。在本质上脆性的结晶固体，特别是钢中，断裂模式从脆性解理到韧性形式的转变，或者反之亦然，是一种既有基本科学意义又有确保结构安全的巨大技术重要性的现象。

9906613ArgonThe important role of grain boundaries in polycrystalline steel in suppressing the brittle-to-ductile (B-D) transition temperature by promoting plastic relaxation processes is well documented. However, the actual forms of this beneficial interaction are inadequately understood. In recent fundamental experimental and theoretical considerations of thermally initiated B-D transition in the propagation of cleavage cracks, it is clear that repeated mechanical arrest of such cracks by grain boundaries promotes plastic relaxations that have distinct beneficial effects in suppressing the B-D transition temperatures. Accordingly, a comprehensive research program is planned involving the experimental measurement of the fracture resistance of a broad selection of individual grain boundaries in large bi-crystals of a Fe-3% Si alloy, harvested from a large ingot containing a range of grain sizes. Additional experimental research examines the thermally stimulated B-D fracture transitions in Fe-3% Si single crystals to develop a clear understanding of the dislocation mechanisms governing the transition. Complementary experiments are planned on the topological features of cleavage fracturing through finer-grained polycrystalline panels. These measurements of boundary cracking resistance and other noted aspects of percolation of cleavage fracture through a field of grains are incorporated into models of global cleavage cracking resistance. The models should have immediate applicability in engineering practice for dealing with the B-D transition not only in the lower shelf region but also in the upper shelf region.%%%Transitions in fracture mode from brittle cleavage to ductile forms, or vice versa, in intrinsically brittle crystalline solids, particularly steels, is a phenomenon of both basic scientific interest and immense technological importance in assuring safety in structures.***