Columnar grain growth during annealing prior to cold rolling of non-oriented electrical steels

Abstract

The present research reports the microstructural factors that favor the development of columnar grains during annealing prior to cold rolling (APCR). Results show that decarburization of steel has a strong effect on phase transformations, grain structure and crystallographic texture. Annealing at 850 °C (two-phase field) promotes the development of columnar-grained microstructures with orientations close to the ideal cube texture. Higher annealing temperatures within the intercritical region, results in a mixture of columnar + equiaxial grains (875 °C) or completely equiaxial-grained microstructures (900 °C). Annealing at temperatures within the single ferrite (700 °C, 750 °C) or austenite (950 °C, 1050 °C) phase fields does not promote the development of columnar grains. In these cases, annealing promotes the development of equiaxial grains with rotated cube texture and orientations along the γ-fibre. Changes in texture produced by APCR are consistent with the Bain and Kurdjumov-Sachs correspondence relationships and occur according to oriented nucleation and selective growth mechanisms depending on the characteristics of decarburization.