The temperature (T) of a metal (1) can be influenced directly or indirectly by at least one actuator (2) which is actuated in accordance with a control variable (S). The control variable (S) and starting values (TA, p1A, p2A) for a temperature of the metal (1) and phase proportions in which the metal (1) is at least in a first phase or a second phase, respectively, are predetermined for a material model (5). A heat conduction equation and a transformation equation are solved in real time within the material model (5), taking account of these variables (TA, p1A, p2A) , and in this way expected values (TE, p1E, p2E) are determined for these variables. As part of the transformation equation, the Gibbs' free energies (G1, G2) of the phases of the metal (1) are determined, a transformation rate of the metal (1) from the first phase to the second phase is determined therefrom, and the expected proportions (p1E, p2E) are determined from the latter.