Ex-Situ Time Sequential Observation on Island and Peninsular Grains in Abnormally Growing Goss Grains in Fe-3%Si Steel

Evolution of abnormally growing Goss grains in Fe-3%Si steel was observed time sequentially by electron backscattering diffraction (EBSD). For example, some specimens were heated at 1080 degrees C for 5 min, then cooled, polished and observed by EBSD, whose procedure was repeated for 6 times. After each heat treatment at 1080 degrees C, the abnormal grain growth morphology of Goss grains in Fe-3%Si steel could be observed by polishing away a thin layer of the oxidized surface. Goss grains grew abnormally in a highly irregular way. As a result, some matrix grains were isolated at the growth front, which produced island grains. The irregular growth often resulted in incomplete isolation, which produced peninsular grains. Numerous matrix grains were isolated by the impingement of abnormally growing Goss grains. Once matrix grains became isolated, island or peninsular grains, they shrank much faster than before. If the grain boundary mobility of island and peninsular grains is not low enough, they would shrink in an accelerated way because their local curvature of grain boundary becomes larger as they shrink. Therefore, the high shrinking rate of island and peninsular grains indicates that island and peninsular grains are formed not because of their low grain boundary mobility but because of solid-state wetting.