Transformed ferrite growth was studied using a dual-phase steel cooled at a rate of 0.1℃/sec after intercritical annealing at 830℃ for 30min. A local equilibrium model assuming a diffusion-controlled reaction has been developed to estimate the growth extent of transformed ferrite as a function of time during cooling. The extent of transformed ferrite grown during cooling to temperature T₂X_(T2), is estimated by the following equation: (수식) However, when cooled to temperature T₃ below T₂ at which diffusion fields of separate transformed ferrite begin to overlap, X_(T3) is given as fellows: (수식) The predicted extent of transformed ferrite agreed well with the experimentally measured data.