The cracking behaviour of the oxide layer formed during hot rolling has been studied together with different combinations of process parameters in order to find their single influence on the surface quality and formation of oxide defects. Several trials have been performed on the CRM pilot line to study in detail the impact of strip reduction, strip temperature, entry scale thickness, roll degradation, lubrication, skin cooling, chemical composition and humidity on the scale behaviour. In general the degree of deformation, entry scale thickness and rolling temperatures are the more important parameters and the importance decreases in that order.