Patent ID: 8458887

Claim:
A method of continuously or semi-continuously direct chill casting an ingot made of a castable metal, comprising the steps of: (a) providing a direct chill casting mold having one or more mold inlets and one or more mold outlets; (b) supplying molten metal to at least one inlet of the casting mold; (c) cooling the mold to solidify a peripheral portion of the metal, thereby forming an embryonic ingot having an external solid shell and an internal molten core; (d) continuously advancing the embryonic ingot beyond at least one outlet of the mold, thereby extending the molten core contained within the solid shell beyond said at least one outlet of the mold; (e) cooling the embryonic ingot emerging from the mold to continue the solidification thereof by directing a supply of coolant liquid onto an outer surface of the embryonic ingot; (f) causing said coolant liquid to be removed from the surface of the embryonic ingot before the ingot has been transformed into a fully solid ingot such that internal heat from the molten core reheats the solid shell adjacent to the core, thereby causing temperatures of said core and said shell to equilibrate at a convergence temperature, said coolant liquid being removed from said surface at a distance from said at least one mold outlet that causes said convergence temperature to be above a transformation temperature at which said metal undergoes in-situ homogenization; (g) cooling said ingot or allowing said ingot to cool; (h) with no intervening homogenization, pre-heating said ingot to a temperature effective for hot rolling; and (i) hot rolling said ingot; wherein said pre-heating of step (h) is carried out in two steps, a first of which comprises heating said ingot to a nucleating temperature below said temperature effective for hot rolling and holding at said nucleating temperature for a time effective to cause nucleation within said ingot, and a second of which comprises heating said ingot from said nucleating temperature to said temperature effective for hot rolling, and maintaining said ingot at said temperature effective for hot rolling for a period of time to allow crystal growth before said hot rolling of step (i).