Abnormal grain growth in thin wires of commercially pure iron with anisotropic microstructure

This work reports the behavior of annealed commercially pure cold-drawn thin iron wires. Primary recrystallization is complete after holding for 180 s at 1123 K. After recrystallization, grain growth takes place within the central region but not close to the surface. For annealing times up to 14400 s, the grain size distribution broadens and the texture strengthens. The resulting texture is intense along the direction parallel to the wiredrawing direction (WD). For longer times, abnormal grain growth takes place. The center of the wire is the preferred place for abnormal grain growth. By contrast, the grains closer to the surface do not experience any growth, and abnormal grains cannot consume them. Throughout the microstructure, one finds AlN and MnS particles. Close to the wire surface, there is a significantly higher particle density than in the center. We discuss mechanisms for the onset of abnormal grain growth, considering particle pinning and crystallographic texture. We observed two kinds of abnormal grains. Most abnormal grains belonged to the // WD fiber texture component, whereas a minority did not. We propose two mechanisms of abnormal grain growth initiation. The first mechanism explains the initiation of the abnormal grains with the assistance of the texture. The second mechanism associates the formation of a candidate abnormal grain to the topological path of the largest grains during normal grain growth preceding the onset of abnormal grain growth.