Abstract The precipitation and dissolution of cementite in austenitic medium Mn high C steels capable of deformation-induced twinning were studied based on the associated length changes. In continuous dilatometry heating cycles, the net contraction associated with the precipitation of cementite resulted in a decrease in the apparent coefficient of thermal expansion. The expansion associated with the reverse process of cementite dissolution in austenite, on the other hand, increased the apparent coefficient of thermal expansion. The contraction associated with the cementite precipitation was found by in-situ X-ray diffraction measurements to originate from the decrease in the lattice parameter of austenite. The latter contraction more than offset the expansion expected based on the pure consideration of austenite replacement by cementite. A model was developed to determine the evolution of cementite fraction based on the dilatometry data and the corresponding X-ray diffraction results during continuous heating cycles. The introduced dilatometry method confirmed the effect of aluminum in retarding the cementite precipitation in medium Mn high C steels.