Abstract: For two cold-rolled low carbon steel with different compositions, the effects of heating rates and specimens' compositions on phase transformation during rapid heating were investigated using Gleeble-3800 thermal simulation testing machine, as well as the evolution of austenite grain size. The results show that the phase transformation temperature increases rapidly with increasing the heating rate from 5 to 100°C/s and then slowly from 100 to 500°C/s. There is a key temperature during continuous heating, i. e., 1050°C, at which austenite grains begin to grow abnormally. The average grain size is less than 5 μm at 850-950°C. Adding alloy elements is beneficial to refining austenite grains. The results provide a reference to obtain the cold-rolled ultrafine grained steel using the method of rapid heating followed by holding for a short time.