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Microstructure and texture evolution of a 0.04%C steel subjected to an isothermal annealing

Abstract:

This work describes the effect of heating rate and annealing time on the microstructure and texture of a 0.04%C steel, cold rolled up to 80%. The samples were subjected to isothermal annealing at heating rates of 12°C/h, 20°C/h, 40°C/h and 650°C/min., followed by 15 hours soaking at 700°C. By the use of Optical Microscopy, Scanning and Transmission Electron Microscopy, the microstructural evolution of the samples was evaluated during the heating process and the holding time at 700°C. Electron Back-Scattered Diffraction (SEM-EBSD) data as well as the results from conventional mechanical testing were used to reveal texture and plastic anisotropy of the samples. Several important features found are: a) Recrystallization occurred between 600 and 650°C. b) At low heating rates (12°C/h, 20°C/h and 40°C/h), the grain structure developed was the so called "pancake". c) The samples heated at low heating rates and annealed at 700°C do not show appreciable grain growth. These results were associated with the precipitation of AlN before recrystallization. d) The samples heated at 650°C/min, exhibited an equiaxial grain structure and important grain growth during the annealing process at 700°C. The texture measurements illustrated that only at low heating rates (12°C/h, 20°C/h and 40°C/h), the material developed a strong recrystallization texture {111} 〈uvw〉, which is in accordance with the high values of the plastic anisotropy found.