Tundish upper nozzle structure and continuous casting method

Abstract

A tundish upper nozzle structure and a continuous casting method make it possible to cause inclusions to float within a tundish. A flange-shaped member having an outside dimension greater than that of an upper end of a tundish upper nozzle is provided along a part or the entirety of the circumference of the upper end of the tundish upper nozzle, and one or more gas discharge holes are provided in one or more of the following surfaces: a lower surface, an outer peripheral surface and a top surface of the flange-shaped member, and a region of an outer peripheral surface of the tundish upper nozzle below the flange-shaped member. A length in the tundish upper nozzle structure is adjusted to cause almost all gas to float upwardly, or to adjust the flow rate of gas flowing downwardly toward the inner bore of the tundish upper nozzle, and the flow rate of gas floating upwardly.

1 . A tundish upper nozzle structure comprises: a tundish upper nozzle; and a flange-shaped member having an outside dimension greater than that of an upper end of the tundish upper nozzle, the flange-shaped member being provided along a part or an entirety of a circumference of the upper end of the tundish upper nozzle, wherein the tundish upper nozzle structure has one or more gas discharge holes provided in one or more surfaces selected from the group consisting of a lower surface, an outer peripheral surface and a top surface of the flange-shaped member, and a region of an outer peripheral surface of the tundish upper nozzle below the flange-shaped member. 
     
     
         2 . The tundish upper nozzle structure as claimed in  claim 1 , wherein the gas discharge hole is provided in the flange-shaped member, wherein the gas discharge hole is an end of a gas distribution passage which is an internal space of the flange-shaped member, or a through-hole penetrating between the lower surface and the top surface of the flange-shaped member. 
     
     
         3 . The tundish upper nozzle structure as claimed in  claim 1 , wherein the lower surface of the flange-shaped member is provided with one or more grooves each allowing gas to pass therethrough. 
     
     
         4 . The tundish upper nozzle structure as claimed in  claim 1 , which is configured such that, in a state in which the tundish upper nozzle structure is attached to a tundish, a space allowing gas to pass therethrough is defined along a part or an entirety of the lower surface of the flange-shaped member. 
     
     
         5 . The tundish upper nozzle structure as claimed in  claim 1 , which is used for operation of continuous casting of steel in which a flow rate of molten steel is controlled by a stopper, wherein a length L (mm) from a position on a vertical extension of an inner bore surface at a lower end of the tundish upper nozzle to the gas discharge hole in the top surface of the flange-shaped member or the outer peripheral surface of the flange-shaped member satisfies the following formula 1:
     L≥− 1.875 M   2 +26.332 M− 0.3929, where  M  denotes a casting speed(t/min).   
     
     
         6 . The tundish upper nozzle structure as claimed in  claim 1 , which is used for operation of continuous casting of steel in which a flow rate of molten steel is controlled by a stopper, wherein a length L (mm) from a position on a vertical extension of an inner bore surface at a lower end of the tundish upper nozzle to the gas discharge hole in the top surface of the flange-shaped member or the outer peripheral surface of the flange-shaped member satisfies the following formula 2:
     L<− 1.875 M   2 +26.332 M− 0.3929, where  M  denotes a casting speed(t/min).   
     
     
         7 . The tundish upper nozzle structure as claimed in  claim 1 , wherein the length L (mm) from the position on the vertical extension of the inner bore surface at the lower end of the tundish upper nozzle to the gas discharge hole in the top surface of the flange-shaped member or the outer peripheral surface of the flange-shaped member is 60 mm or more. 
     
     
         8 . The tundish upper nozzle structure as claimed in  claim 1 , wherein the flange-shaped member is joined to the tundish upper nozzle. 
     
     
         9 . The tundish upper nozzle structure as claimed in  claim 8 , wherein the flange-shaped member and the tundish upper nozzle are joined together by a screw, or a bayonet structure, or an adhesive. 
     
     
         10 . The tundish upper nozzle structure as claimed in  claim 1 , wherein the flange-shaped member is fitted onto an outer periphery of the tundish upper nozzle, and joined to a tuyere adjacent to the tundish upper nozzle, or a refractory layer in a bottom of a tundish. 
     
     
         11 . The tundish upper nozzle structure as claimed in  claim 10 , wherein the flange-shaped member, and the tuyere or the refractory layer in the bottom of the tundish, are joined together by a screw, or a bayonet structure, or an adhesive. 
     
     
         12 . A continuous casting method using the tundish upper nozzle structure as claimed in  claim 1 , wherein the tundish upper nozzle structure is used for operation of continuous casting of steel in which a flow rate of molten steel is controlled by a stopper, the continuous casting method comprising: setting a length L (mm) from a position on a vertical extension of an inner bore surface at a lower end of the tundish upper nozzle to the gas discharge hole in the top surface of the flange-shaped member or the outer peripheral surface of the flange-shaped member, to be equal to or greater than a boundary length LB (mm) satisfying the following formula 3, thereby causing almost the entirety of the gas to float upwardly; or setting the length L (mm) to be less than the boundary length LB (mm), to adjust a flow rate of gas flowing downwardly toward an inner bore of the tundish upper nozzle, and a flow rate of gas floating upwardly;
     L=− 1.875 M   2 +26.332 M− 0.3929, where  M  denotes a casting speed(t/min).