The first part of this diploma thesis deals with calculating ortho- and paraequilibrium for a quaternary FeMnSiC-system using the sublattice model (the substitutional components and the interstitial components are occupying different lattice sites). The chemical potentials of the four components (Fe, Mn, Si and C), obtained from molar Gibbs energies of these two phases, are used to simulate the kinetics of diffusional gamma/alpha phase transformation of the steel 10MnSi7. By means of a transformation routine - based on the sharp interface approximation (infinitely small thickness of the interface) - the coupled problem of finite mobility and carbon bulk diffusion controlled interface migration during the phase transformation is solved. The input parameters of the kinetic routine - implemented in Fortran - are the temperature regime, the initial size of the austenite grain, the chemical composition of the steel 10MnSi7, the diffusion coefficient of carbon in austenite and the effective mobility of the migrating interface as a fit parameter. The calculations are based on the assumption of immobile substitutional components in the bulk phases, which means that the molar Fe/Mn and Fe/Si ratios remain constant during the transformation and are of the same value in both phases. In order to determine the kinetics of the diffusional phase transformation experimentally, dilatometer tests with the thermo-mechanical testing machine Gleeble 3800 are accomplished. The isothermal transformation characteristics of this steel grade are investigated for two cylindrically shaped samples in the temperature range between 705 °C and 765°C. By comparing experimental and modeling results it is observed that the gamma/alpha phase transformation is described reasonably well in the investigated temperature range. As an underlying assumption the kinetics is modeled by assuming a spherical shell growing to its center. The diffusion processes in the interface are considered by an effective interface mobility which serves as a fit parameter. It is observed that for the steel composition investigated in this diploma thesis diffusion processes in the interfacial region are relevant only for substitutional components and not for interstitially dissolved carbon. This can be underlined by the dimensionless Péclet-number giving an estimate of the influence of diffusion processes on the transformation kinetics.