Recrystallization Behaviour and Textures in Extra-low Carbon Steel Sheets with Ununiform Distribution of Nitrogen Levels to the Plane Normal Direction

Abstract

Effects of nitrogen content and their diffusion on the recrystallization were investigated for extra-low carbon steel sheets (0.13% Mn). Decarburized sheets with three kinds of nitrogen level distribution to the plane normal direction(PN) were adjusted by atmosphere reaction ; (i) higher nitrogen level in surface layer than neutral layer (series A), (ii) uniform distribution (Series B) and (iii) inverse distribution to Series A (Series C). Each Series was classified into several average nitrogen contents(2-94 ppm). These were heavily cold-rolled and then annealed up to 750°C. Nucleation temperature was increased with average nitrogen content for each Series, while the 50%-recrystallization temperature was decreased with average nitrogen content for Series A and C. In the case of higher nitrogen content in average, the augmentation of (111) component by annealing process was large on both the neutral layer of Series A and the surface layer of Series C, where the grain growth to PN was frequently observed. It was inferred that the enhancement of (111) recrystallization textures was affected by the diffusion of nitrogen atoms dissolved from nitride on annealing stage.