In case of an in-vessel corium retention (IVR) the deterioration of vessel steel properties can be caused both by the steel melting and by its physicochemical interaction with corium. The interaction behavior has been studied in the medium-scale experiments with a prototypic corium within the METCOR project. The resulting experimental data give an insight into the steel corrosion at its interaction with UO2+x-ZrO2-FeOy melt in air and steam. It has been established that corrosion rate is practically the same in air and steam atmosphere; if the temperature on the interaction interface grows beyond a certain level, corrosion intensifies, which is explained by the formation of specific fusible phases in the interaction zone. The available experimental data have been used for developing a correlation of corrosion rate versus heat flux density and temperature.