Ferrite grain refinement of Ti-added low carbon steel through dynamic recrystallization in austenite region

摘要

Effect of grain size and deformation condition on dynamic recrystallization behavior of Ti-added low carbon steel in austenite region was studied mainly through hot-compression test. When initial austenite grain size was smaller than 50 pm, a peak of true stress, which is characteristic of dynamic recrystallization, was observed even in high Z (Zener-Hollomon parameter) region such as at 1123K and at the strain rate of 0.4/s. The small austenite grain can be obtained when more than 0.15% Ti is added and the steel is reheated at the temperature of lower than 1423K. In this case, it is considered that TiC precipitates should prohibit the grain growth of austenite during heating. The peak stresses in various deformation conditions were expressed by Z parameter, from which the apparent activation energy was calculated as 340 kJ/mol. The typical final grain size of ferrite after dynamic recrystallization and transformation at the cooling rate of 50K/s was 2～5 μm. It is estimated that the effect of solute C and solute Ti on dynamic recrystallization was very limited.