Modelling of laser surface hardening of AISI 4140 steel including the effect of inhomogeneous austenite formation due to locally different austenizing and quenching conditions is carried out to gain a better understanding of the material reaction during short-time hardening processes. Dilatometric studies at high heating and cooling rates lead to base informations for material laws reflecting the influence of the inhomogeneity of austenite on the quenching process. They were implemented in the finite-element-program ABAQUS as user defined material laws and allow a coupled calculation of temperature and phase development during heating and cooling. The influence of heating rate and cooling rate on the time-dependent temperature fields and phase transformations within the affected zone was investigated. A good correspondence between the results of simulation and experimental data was obtained in respect of the resulting hardness profiles and the degree of homogeneity of the hardened structure.