Effects of decarburization and normalizing heat treatment in boron-silicon iron alloys

Abstract

Effects of carbon content and various heat treatments on the secondary recrystallization in boronsilicon iron have been studied by measurement of induction at a magnetizing force of 800 A/m and examination of microstructures at various stages of sample preparation process. Carbon was varied before and after hot rolling by adding carbon to the melts and by oxide decarburization of hot bands at 700 °C. Results show that complete secondary recrystallization and high induction (1.92 Tesla) are obtained from heats whose hot bands have been decarburized at 700 °C to a level of 30 to 40 ppm provided the heats contained 0.039 to 0.049 wt Pct carbon during heating for hot rolling. From these facts and analysis of microstructures of cross-sectional area of specimens at various stages of process it can be said that one of the major roles that carbon plays is to introduce, through transformation of austenite, a nonuniform layer-like microstructure during hot rolling and during the normalizing heat treatment of the hot band. This structure continues to exist in the final cold rolled sheet and results in anisotropic growth of secondary grains, and plays a significant role in the secondary recrystallization of boron-silicon iron.