Effect of acicular ferrite on mechanical properties of hot-rolled ultra-fine grain microalloyed steels

In consideration of the high tensile strength but low elongation properties of ultra-fine grain microalloyed steels prepared by deformation-induced phase transformation rolling technology, microstructural quantitative analysis was conducted. Results show that the volume ratio of acicular ferrites is mainly influenced by cooling rate, the higher the cooling rate is, the more acicular ferrites are obtained. By increasing the volume ratio of acicular ferrites, the tensile strength increases; On the other hand, the elongation reduces markedly because of the morphological characteristics, needle effect, size factor of acicular ferrites and so on. By adjusting the cooling rate in cooling process, the volume ratio of acicular ferrites can be controlled in the optimum range, so as to improve the comprehensive mechanical properties of steel.