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

Grain boundary shapes and grain growth in bulk 2.61 wt% silicon-iron, have been studied by heat-treating at temperatures between 700 and 1200degreesC. Initial microstructure with fairly uniform fine grains has been obtained by recrystallization at 800degreesC for 5 min after deformation. When subsequently heat-treated at 700 and 800degreesC, a fraction of the grain boundaries have hill-and-valley shapes with several facet planes or kinks. Some of the se facet boundary segments are expected to be singular. Abnormal grain growth occurs at 700 and 800degreesC and is attributed to step growth of the boundaries. When heat-treated at 1000degreesC, all grain boundaries are defaceted with smoothly curved shapes, indicating that they are atomically rough. At temperatures above 1000degreesC, 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.