Workpieces of a low carbon steel (LCS) are deformed by equal-channel angular pressing (ECAP) up to an equivalent strain of 6 in their as-received, coarse-grained condition. ECAP of LCS produces an ultrafine-grained (UFG) banded structure of 0.6 μm in width, with a high dislocation density and lattice strain. Though the refinement improves strength significantly, the material suffers from a detrimental low ductility. ECAPed samples are therefore electropulsed to recover the ductility to a large extent. A mechanism, by which a unique microstructure that fecilitates the regainment of ductility, is proposed in this study. Electropulsing (EP) creates additional low angle grain boundaries (LAGBs) by electromigration of dislocations within the grain and leads to the migration of high angle grain boundaries (HAGBs) under high electron wind force. Groups of subgrain boundaries move towards high angle grain boundaries and coalesce, producing a region of relatively lower defect density, i.e., the formation of recrystallized nuclei. On further pulsing, the HAGBs of the recrystallized nuclei continue to migrate and eventually impinge on each other. As a result, a bimodal grain size distribution consisting of micron-sized, near-equiaxed grains that are favorably interspersed with UFG grains occurs, and has a low defect density. The microstructure is clear of any residual strain. Upon electropulsing the strength of ECAPed LCS is marginally traded off for a larger gain in ductility. The micron-sized grains of the bimodal distribution are understood to accommodate larger deformations and enhance the ductility.

低碳钢 (LCS) 工件通过等通道角挤压 (ECAP) 变形，在其收到的粗晶粒状态下，等效应变达到 6。LCS 的 ECAP 产生 0.6 μ的超细晶 (UFG) 带状结构米宽，具有高位错密度和晶格应变。尽管这种改进显着提高了强度，但该材料的延展性较低。因此，对 ECAPed 样品进行电脉冲以在很大程度上恢复延展性。本研究提出了一种促进延展性恢复的独特微观结构的机制。电脉冲 (EP) 通过晶粒内位错的电迁移产生额外的低角度晶界 (LAGB)，并在高电子风力下导致高角度晶界 (HAGB) 的迁移。亚晶界群向大角度晶界移动并聚结，产生一个缺陷密度相对较低的区域，即.，形成重结晶核。在进一步脉冲时，重结晶核的 HAGB 继续迁移并最终相互碰撞。结果，出现由良好地散布有UFG晶粒的微米级、近等轴晶粒组成的双峰晶粒尺寸分布，并且具有低缺陷密度。微观结构没有任何残余应变。在进行电脉冲时，ECAPed LCS 的强度会略微折衷以获得更大的延展性增益。双峰分布的微米级晶粒被理解为适应更大的变形并增强延展性。