AbstractWe consider an optimal control problem concerning heat treatment of steel. The mathematical model consists of the equations of thermoelasticity coupled to a system of rate laws accounting for the phase transition kinetics. For the coupling a mixture ansatz for the different thermal expansion coefficients is used. In contrast to classical thermoelasticity this leads to residual deformations whenever the resulting phase distribution at end‐time is inhomogenous. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)