Method for continuously casting steel billet strands to minimize the porosity and chemical segregation along the center line of the strand

Claim 1

In the continuous casting of steel billet strands which involves teeming molten steel from a tundish at a controlled rate into a continuous casting mold wherein a solidified skin is formed on the billet strand and progressively withdrawing such billet strand from the mold, the improvement which comprises the steps of: a. controlling heat transfer from the billet strand in the region immediately below said mold to allow progressive increase in thickness of said skin due to transverse solidification of the molten steel contained by said skin only to that extent to provide a progressive skin thickening in transverse freezing mode which is capable of withstanding the metallostatic head of the molten core and which consequently is significantly less than that amount which would favor transverse solidification all the way to the center line of the billet strand; b. continuing the controlled cooling of the billet strand in the manner specified in step (a) until the temperature of the molten steel at the center line of the billet strand has decreased to that temperature which favors vertical solidification thereof; and then c. cooling the billet strand to complete solidification of its central region in the vertical solidification mode; the controlled cooling of steps (a) and (b) being effected by water spray applied to the external surface of the billet strand and including the step of cooling the molten steel after it passes through the tundish nozzle and while entering the mold to about its liquidus temperature.

Claim 20

The method of continuously casting steel to produce a billet strand of indefinite length with minimal porosity and chemical segregation along the center line of the billet strand, which comprises the steps of: a. teeming molten steel from a tundish at a temperature sufficiently higher than the liquidus temperature of the steel to insure against plugging of the tundish nozzle, and directing such steel into a continuous casting mold at a controlled rate; b. cooling the molten steel to about its liquidus temperature as it enters the mold; c. forming a skin of sufficient thickness around the billet strand with said mold to withstand metallostatic head of molten steel as the billet strand emerges from the mold; d. controlling the cooling of the emergent billet strand by extracting heat therefrom at a rate only to that extent to provide a progressive skin thickening in transverse freezing mode which is capable of withstanding the metallostatic head of the molten core and which consequently is significantly less than that rate which would favor transverse solidification across the entire cross sectiOn of the billet strand whereby the center of the billet strand remains in molten condition, and continuing such controlled cooling until the temperature of molten steel at the center of the billet strand reaches that value which favors vertical solidification thereof; and then e. radiantly cooling the billet strand to complete solidification of the molten steel at the center of the billet strand in the vertical mode.

Claim 21

The method of continuously casting steel to produce a billet strand of indefinite length with minimal porosity and chemical segregation along the center line of the billet strand, which comprises the steps of: a. teeming molten steel from a tundish at a temperature sufficiently higher than the liquidus temperature of the steel to insure against plugging of the tundish nozzle, and directing such steel into a continuous casting mold at a controlled rate; b. cooling the molten steel to about its liquidus temperature as it enters the mold; c. forming a skin of sufficient thickness around the billet strand with said mold to withstand metallostatic head of molten steel as the billet strand emerges from the mold; d. controlling the cooling of the emergent billet strand by extracting heat therefrom at a rate only to that extent to provide a progressive skin thickening in transverse freezing mode which is capable of withstanding the metallostatic head of the molten core and which consequently is significantly less than that rate which would favor transverse solidification across the entire cross sectiOn of the billet strand whereby the center of the billet strand remains in molten condition, and continuing such controlled cooling until the temperature of molten steel at the center of the billet strand reaches that value which favors vertical solidification thereof; and then e. radiantly cooling the billet strand to complete solidification of the molten steel at the center of the billet strand in the vertical mode.