Effect of precipitates on grain growth in non-oriented silicon steel

Precipitates and grain sizes in non-oriented silicon steel samples, which were hot-rolled (HR), continuously annealed (CA), and stress-relief-annealed (SA), were characterized using scanning electron microscopy (SEM) equipped with electron back-scattered diffraction. The average grain sizes of the HR, CA, and SA samples were 28, 46, and 46 μm, respectively. SEM observations revealed that the precipitates were mainly dispersed inside grains in the HR and the CA samples, but mainly at grain boundaries in the SA sample. The density of precipitates was highest in the SA sample and lowest in the HR sample. Precipitates at the grain boundaries, which were identified as manganese sulfides, were nearly spherical, their diameter ranging from 0.3 to 0.7 μm. We calculated the pining force exerted by grain-boundary precipitates and found that it outweighed the driving force of the grain growth that was controlled by boundary curvature.