It is very important to understand interstitial carbon behaviors in cold rolled steel to get the good formability as well as the high strength. In low carbon steel, most of carbons are consumed by the formation of grain boundary cementite during cooling. During heating and holding between Ae1 and Ae3, cementite is dissolved and consequently carbon enriched austenite is formed. By controlled cooling, retained austenite as well as bainite and martensite are formed. In this study, the effect of silicon, intercritical annealing, isothermal bainite transformation on the formation of ferritic bainite, cementite and retained austenite are modeled by nucleation and growth, diffusion and dissolution. In addition, the formation of retained austenite and their carbon contents are modeled and compared with experimental data.