The copper enrichment behaviours of several copper-containing steels under conditions similar to those in the thin-slab casting processes are examined. Formation of a molten copper phase at the scale-steel interface can be avoided when the substrate phase is occluded in the scale during steel oxidation. Significant enrichment of nickel in the surface layer of the substrate is a necessary condition for the occlusion of the substrate phase into the scale before the precipitation of a molten copper phase. The critical nickel content above which the occlusion mechanism would be operative is between 0.02 % and 0.07 %. The critical temperature above which the occlusion mechanism becomes operative in the high nickel steels differs when the isothermal oxidation step, following continuous cooling in ambient air, is conducted in different atmospheres. When conducted in ambient air, this temperature is between 1150°C and 1230°C, whereas when conducted in moist air or in simulated furnace atmospheres, it is lowered to between 1100°C and 1150°C. Preferential oxide growth along the grain boundaries of the substrate is another important occlusion mechanism, however, the deep oxide penetrations in the substrate may lead to descaling difficulty.