Abstract: Cold-drawn pearlitic steel wire is widely used because of its high strength and certain toughness. In the process of cold drawing, the evolution of cementite lamellae has an important influence on the strength and toughness of steel wire. In this work, high-carbon steel wire rod with a diameter of 7.81 mm is selected, and the series of high-strength pearlite steel wires with different diameters are obtained by multi-pass cold drawing until the maximum true strain reached to 2.18. The evolution law and microscopic mechanism of cementite lamellae evolution during cold drawing are observed by transmission electron microscope (TEM) and scanning electron microscope (SEM) methods. The results show that during steel wire drawing, the longitudinal fibrous pearlite structure becomes more obvious with the increase of strain, and pearlite lamellae composed of ferrite and cementite are gradually adjusted to the drawing direction, and all of them are parallel to the drawing direction at the strain of 2.18. Complex changes have taken place in the cementite lamellae during drawing, which are characterized by lamellar refinement, bending and fracture in morphology, and polycrystalline, amorphous and nanocrystalline phenomena in microstructure. When the pearlitic lamellar orientation is nearly parallel to the drawing direction, interlamellar spacing gradually decreases, the lamellar arrangement direction gradually turns to the drawing direction, and the cementite lamellae become amorphous and nanocrystalline. When pearlite lamellae are nearly perpendicular to the drawing direction, cementite lamellae are bent, fractured and crystallized. At low drawing strain, dislocations mainly move in ferrite phase with a single slip, forming dislocation lines. At high strain, dislocations transform into multi-slip motions, generating dislocation tangles and dislocation cells, and some dislocations slip across the α-ferrite/cementite interfaces. Dislocation interacts strongly with cementite, and the lattice distortion in cementite increases, which is the main reason for the complex changes of cementite lamellae during cold drawing.

Key words: pearlite steel wire, drawing, cementite, dislocation slip, microstructure

摘要： 冷拔珠光体钢丝因具有高强度和一定的韧性而获得广泛应用。冷拔过程中，渗碳体片层演变对钢丝强韧性有重要的影响。本工作选用直径为7.81 mm的高碳钢盘条，通过多道次冷拉拔至最大真应变2.18，获得系列高强度珠光体钢丝。通过透射电子显微镜(TEM)和扫描电子显微镜(SEM)观察盘条拉拔过程中渗碳体片层的演变规律及其微观机制。结果表明，在钢丝拉拔过程中，珠光体纤维化程度不断增强，由铁素体和渗碳体构成的珠光体片层逐渐向拉拔方向调整，在真应变为2.18下全部平行于拉拔方向。拉拔过程中渗碳体片层发生了复杂的变化，形貌上表现为片层细化、弯曲和断裂，微观结构上出现了多晶化、非晶化和纳米晶化等现象。珠光体片层取向与拉拔方向近平行时，片层间距逐步减小，片层排列方向逐渐转到拉拔方向，渗碳体片层发生了非晶化和纳米晶化等现象。珠光体片层与拉拔方向近垂直时，渗碳体片层发生了弯曲、断裂和多晶化。拉拔过程中，位错与渗碳体强烈交互作用，渗碳体内晶格畸变增大，是渗碳体片层发生复杂变化的主要原因。

关键词: 珠光体钢丝, 拉拔, 渗碳体, 位错滑移, 微观结构