Temperature dependence of grain boundary structure and grain growth in bulk silicon-iron

Abstract

Grain boundary shapes and grain growth in bulk 2.61 wt% silicon-iron have been studied by heat-treating at temperatures between 700 and 1 200°C. Initial microstructure with fairly uniform fine grains has been obtained by recrystallization at 800°C for 5 min after deformation. When subsequently heat-treated at 700 and 800°C, a fraction of the grain boundaries have hill-and-valley shapes with several facet planes or kinks. Some of these facet boundary segments are expected to be singular. Abnormal grain growth occurs at 700 and 800°C and is attributed to step growth of the boundaries. When heat-treated at 1 000°C, all grain boundaries are defaceted with smoothly curved shapes, indicating that they are atomically rough. At temperatures above 1 000°C, normal grain growth occurs, because the rough grain boundaries move continuously. This correlation between grain boundary structure and grain growth is consistent with the earlier observations in other metals and oxides. It is thus shown that the abnormal grain growth in this alloy occurs at low temperatures because of the singular grain boundary structure.