In the current work, nanostructured pearlitic steels in bulk with interlamellar spacing of 86 and 168 nm, respectively, are developed through suitable alloying combined with appropriate heat treatment. The specimens extracted from the steels are tested separately in tension and torsion. Under tensile extension, finer pearlite shows a higher yield strength and ultimate tensile strength but fractures at a lower value of strain. However, under torsion testing, finer pearlite deforms to higher shear stress while fracturing at marginally larger shear strain than the coarser pearlite. Under torsion loading, the fractured surface of the finer pearlite presents a larger length of ductile crack propagation (DCP) extending from the circumference toward the center before initiation of cleavage fracture. Scanning electron microscopy (SEM) images of the DCP region are used to characterize the deformation of cementite lamellae, whereas electron backscattered diffraction (EBSD) maps reveal the misorientation changes in ferrite due to torsion. A more frequent and irregular change in ferrite misorientation for coarser pearlite in the DCP region is observed compared with finer pearlite. Bending and fragmentation of cementite lamellae are observed to be higher for fine pearlite, suggesting better strain accommodation. Thus, decreasing the lamellar spacing in nanostructured pearlite improves the torsional response.

中文翻译：

---

拉伸与扭转作用下纳米结构珠光体的形变与微观结构演变

在当前的工作中，通过适当的合金化和适当的热处理，分别开发出层间间距分别为86和168 nm的纳米结构珠光体钢。从钢中提取的试样分别进行拉伸和扭转测试。在拉伸伸长下，较细的珠光体显示出较高的屈服强度和极限拉伸强度，但在较低的应变值下断裂。但是，在扭转试验中，较细的珠光体变形时会产生较高的剪应力，而在断裂时的剪切应变要比较粗的珠光体稍大。在扭转载荷下，较细的珠光体的断裂表面呈现出较大的延性裂纹扩展（DCP）长度，该断裂从断裂开始前从圆周向中心延伸。DCP区域的扫描电子显微镜（SEM）图像用于表征渗碳体薄片的变形，而电子背散射衍射（EBSD）图则显示了由于扭转导致铁素体的取向改变。与较细的珠光体相比，对于DCP区域中较粗的珠光体，观察到铁素体取向差更频繁且不规则的变化。对于细珠光体，观察到渗碳体薄片的弯曲和破碎更高，表明更好的应变适应性。因此，减小纳米结构珠光体中的层状间隔可改善扭转响应。与较细的珠光体相比，对于DCP区域中较粗的珠光体，观察到铁素体取向差更频繁且不规则的变化。对于细珠光体，观察到渗碳体薄片的弯曲和破碎更高，表明更好的应变适应性。因此，减小纳米结构珠光体中的层状间隔可改善扭转响应。与较细的珠光体相比，对于DCP区域中较粗的珠光体，观察到铁素体取向差更频繁且不规则的变化。对于细珠光体，观察到渗碳体薄片的弯曲和破碎更高，表明更好的应变适应性。因此，减小纳米结构珠光体中的层状间隔可改善扭转响应。