The following discussion concerns modelling of fracture in steel plates during an impact test, in which both target and striker are manufactured from the same material, high-strength high-hardness armour steel – Mars® 300. The test conditions (3 mm thick targets, projectiles with different nose shapes at impact velocity lower than 400 m/s) result in severely damaged components, which results in an analysis of stress states showing material failure. Numerical analyses are performed using two material models: the Johnson-Cook approach, as traditionally used in impact simulations, accounting for the effect of stress triaxiality, strain rate and temperature and for comparison, a simulation by means of the stress triaxiality and Lode angle parameter-dependent Hosford-Coulomb model, also incorporating the effect of the strain rate on a fracture initiation. The aim of the study is to analyse the mechanisms of penetration and perforation observed in the armour steel plates and validation of the modelling approaches.