Microstructural evolution of a commercial 0.04%C steel during batch annealing

The effect of heating rate and annealing time on the microstructure and texture of a commercial 0.04 %C steel, cold rolled up to 80 %, is studied. Samples have been isothermally annealed at various heating rates (12 degrees C/h, 20 degrees C/h, 40 degrees C/h and 650 degrees C/min) and then soaked at 700 degrees C for 15 hours. The microstructural. evolution of the samples during the heating process and hold period has been followed by optical microscopy, scanning and transmission electron microscopy. The electron back-scattered diffraction technique is used to reveal the texture of the samples. Tensile tests and hardness measurements are correlated with the microstructural features. Results show that (a) recrystallization occurs between 600 and 650 degrees C; (b) a "pancake" structure develops during recrystallization at low heating rates without appreciable grain growth; (c) samples heated at 650 degrees C/min exhibit an equiaxed grain structure and significant grain growth; (d) only at low heating rates the material develops a strong {111}< uvw > recrystallization texture, in accordance with the high plastic anisotropy found by mechanical testing.