Abnormal growth of columnar grains and formation of Σ3 grain boundaries in non-oriented electrical steels

Abstract

The remarkably abnormal growth behavior of columnar grains and the formation of Σ3 grain boundaries (GBs) were studied via plastic deformation and annealing based on an electron backscattering diffraction (EBSD) investigation. Driven by the stored energy and GB mobility, coarse austenite columnar grains were formed by the abnormal growth of fine equiaxed grains with higher grain orientation spread (GOS) values in the reducing atmosphere of hydrogen. Moreover, extraordinarily coarse columnar grains with high GOS values and non-{1 1 1} texture were formed by microstructure inheritance during γ → α transformation. In addition, slender ferritic columnar or island grains with Σ3 GBs and low GOS values were generally obtained, and the formation mechanism was strictly associated with the Kurdjumov-Sachs (K-S) relationship, which was induced during variant selection driven by the GB mobility and surface effect in the reducing atmosphere of hydrogen.