The problem of determining stresses, phase compositions and temperature distributions during the transformation hardening of steel with a CO-laser beam is investigated. To model the different phases in each material point a parallel fraction model is used, in which each fraction represents one phase. The description of phase transformations is obtained by an incremental formulation of the Avrami-equation for isothermal transformation. A model is developed to describe the superheating of ferrite and pearlite. The model is demonstrated by a detailed computation of stresses, deformations and phase compositions in the case of a stationary laser flash