The cracking behaviour of the oxide layer formed duringhot rolling has been studied together with differentcombinations of process parameters in order to find theirsingle influence on the surface quality and formation ofoxide defects. Several trials have been performed on theCRM pilot line to study in detail the impact of strip reduction,strip temperature, entry scale thickness, roll degradation,lubrication, skin cooling, chemical composition andhumidity on the scale behaviour. In general the degree ofdeformation, entry scale thickness and rolling temperaturesare the more important parameters and the importancedecreases in that order.