Abstract: Based on the analysis of thermodynamics and dynamics for austenization during intercritical annealing of a dual phase steel; an austenization model was established and solved by using the explicit finite volume method at two austenite temperatures of 740℃ and 780℃. The simulated results show that the initial stage of austenite growth is controlled by carbon diffusion in austenite and reaches paraequilibrium quickly, and the austenization rate in this stage is very fast. The late stage of austenite growth is controlled by manganese diffusion in ferrite. As the diffusion rate of manganese is several orders of magnitude slower than that of carbon, this stage lasts for thousands of seconds. When the diffusion flux of manganese in each phase is equal, austenite stops growing. But manganese continues its transfer from ferrite to austenite in order to achieve its homogenization in each phase.