Ferrite precipitation-strengthened steel characterized by a large amount of nano-carbide precipitation has been widely used in the automotive industry to meet its growing energy-reduction requirements. Because of its high strength and excellent tensile flange properties, it has always been of great interest to researchers. Among the topics of interest, the composition of nanoscale carbides and their precipitation behavior have always been a popular subject area of research. In recent years, studies have confirmed that the addition of Cr is beneficial to the formation of nanoscale complex carbide in ferrite and can refine the size of and increase the number density of precipitates, thereby enhancing the strength of the ferrite. The precipitation behavior of carbides is closely related to the phase transformation of ferrite. However, there is controversy about how Cr affects the kinetics of the ferrite phase transition. This study investigated the effect of Cr on the isothermal decomposition behavior of austenite in low-carbon Ti-bearing microalloyed steel using experimental and numerical simulation methods. The driving forces behind the transformation of ferrite and pearlite, as well as the growth kinetics of ferrite, were calculated using Thermo-Calc software for thermodynamics. The reasons for Cr promoting the formation of pearlite were elucidated through first-principles calculations. The isothermal experimental results indicate that Cr element inhibits the nucleation and growth of ferrite and promotes the decomposition of austenite into pearlite. Thermodynamic calculations show that Cr reduces the driving force behind the γ-to-α phase transition, which results in an increase in the critical nucleation radius (r*) and critical nucleation work (ΔG*). Moreover, Cr significantly reduces the diffusion coefficient of C in austenite and increases austenite’s diffusion activation energy (Q_c). The combined effect of both factors leads to the slow nucleation of ferrite. During the growth of ferrite, its phase transformation under negligible-partitioned local equilibrium (NPLE) mode is controlled by C diffusion. Cr reduces the diffusion coefficient of C in austenite, thereby decreasing the growth rate of ferrite. Under partitioned local equilibrium (PLE) mode, the phase transformation is controlled by the diffusion of the alloying elements. Because the diffusion coefficients (D_i) of element i follow the order D_Cr ＜ D_Mn ＜ D_Si, the growth rate of ferrite is slow. Furthermore, Cr element can significantly reduce the Gibbs free energy of the cementite, thereby increasing the driving force of the transformation of pearlite. According to first-principle calculations, Cr atoms tend to substitute for Fe and Mn atoms in cementite, a (Fe, Mn)₃C alloy. Particularly for the Fe atoms, they can markedly decrease the formation energy and promote the precipitation of cementite, thereby facilitating the transformation to pearlite.