Influence of Cu2S precipitates dissolution on ferrite grain growth during heat treatment in the non-oriented electrical steel sheet

Abstract

The factor to deduce grain growth of non-oriented electrical steel sheet during heat treatment was researched in this paper. Scanning electron microscope equipped with electron backscatter diffraction (EBSD), X-ray diffraction and transmission electron microscope were used to characterize the microstructure, dislocation density and precipitate, respectively. The EBSD results indicated that the grain size increased from 18.7 μm to 56 μm after heat treatment. Meanwhile, the characterization of grain size distribution, dislocation density and precipitates revealed that the dissolution of Cu2S precipitates, which act as inhibitor, may lead to the grain growth. In addition, the pinning force of grain boundary and the driving force of grain growth were calculated. Based on experiments results and theoretical calculations, the Cu2S precipitates with diameter of less than 39 nm and volume fraction of 1.74 × 10-4 would be sufficient to inhibit the ferrite grain growth. Heat treatment provides an efficient way to prompt the grain growth.