Immersion nozzle for continuous casting and continuous casting method for steel

Abstract

An immersion nozzle for continuous casting is adapted to discharge molten steel into a mold for continuous steel casting and has a tubular nozzle body which is provided with four molten steel discharge ports consisting of left upper, left lower, right upper and right lower ports which open into a lower end portion of the nozzle body to be immersed into the molten steel in the mold. The two left discharge ports and the two right discharge ports have substantially symmetrical shape with respect to an axis of the nozzle. The left discharge ports are opposed to the inner wall of the left minor side of the mold and the right discharge ports are opposed to the inner wall of the right minor side of the mold. The area of the openings of the lower discharge ports is smaller than the area of the openings of the upper discharge ports. The ratio of the area of the openings of the lower discharge ports to the area of a sum of the areas of the openings of the upper and lower discharge ports is not less than 0.2 but not more than 0.4.

1 . An immersion nozzle for continuous casting which has a shape of a cylinder with a bottom and through which molten steel is poured into a mold for continuous casting, wherein:
 the immersion nozzle has, at a portion to be immersed in the molten steel inside the mold for continuous casting, two or more pairs of discharge ports that are axially symmetrical with respect to an axial center of the immersion nozzle;   in a molten steel flow passage inside a straight body part of the immersion nozzle, an inside diameter in a range from an upper end of an upper discharge port to a bottom of the immersion nozzle is equal to or smaller than that at other portions;   when a one-side opening part area of the upper discharge port is S 3  and a one-side opening part area of the lower discharge port is S 4 ,
 a ratio of a straight-body-part internal cross-sectional area (S 1 ) in a range from an upper end of the immersion nozzle to the upper end of the upper discharge port to a total one-side opening part area (S 3 +S 4 ) of the discharge ports is within a range of 0.30 to 0.50, 
 a ratio of a straight-body-part internal cross-sectional area (S 2 ) in a range from the upper end of the upper discharge port to the bottom of the immersion nozzle to the total one-side opening part area (S 3 +S 4 ) of the discharge ports is within a range of 0.10 to 0.40, and 
 the straight-body-part internal cross-sectional areas (S 1 , S 2 ) of the immersion nozzle and the one-side opening areas (S 3 , S 4 ) of the discharge ports meet a relationship 0.20≤(S 2 /S 4 )≤(S 1 /S 3 )≤1.0; 
   a discharge angle of each of the discharge ports is within a range of +20° to −50°, with an upward direction based on a horizontal plane being positive; and   the discharge angle of the discharge port on a vertically lower side is vertically downward within a range of 20° to 55° based on the discharge angle of the discharge port on a vertically upper side.   
     
     
         2 . The immersion nozzle for continuous casting according to  claim 1 , wherein two of the discharge ports with a vertical positional relationship face different directions in the horizontal plane, and at least one pair of the discharge ports faces a direction parallel to a long-side surface of the mold. 
     
     
         3 . A steel continuous casting method, wherein:
 the immersion nozzle for continuous casting according to  claim 1  is used;   a mold powder is added to a surface of molten steel inside a mold for continuous casting; and   molten steel inside a tundish is poured into the mold through the immersion nozzle, while an inert gas is blown into molten steel flowing down the molten steel flow passage of the immersion nozzle.   
     
     
         4 . The steel continuous casting method according to  claim 3 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while a direct-current static magnetic field is applied to the molten steel inside the mold, on an upper side of a discharge port located at a vertically uppermost part and on a lower side of a discharge port located at a vertically lowermost part of the immersion nozzle, from a direct-current magnetic field generation device installed on a back surface of the mold for continuous casting. 
     
     
         5 . The steel continuous casting method according to  claim 3 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while an alternating-current moving magnetic field is applied to the molten steel inside the mold from an alternating-current magnetic field generation device installed on a back surface of the mold for continuous casting. 
     
     
         6 . The steel continuous casting method according to  claim 4 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while an alternating-current moving magnetic field is applied to the molten steel inside the mold from an alternating-current magnetic field generation device installed on the back surface of the mold for continuous casting. 
     
     
         7 . A steel continuous casting method, wherein:
 the immersion nozzle for continuous casting according to  claim 2  is used;   a mold powder is added to a surface of molten steel inside a mold for continuous casting; and   molten steel inside a tundish is poured into the mold through the immersion nozzle, while an inert gas is blown into molten steel flowing down the molten steel flow passage of the immersion nozzle.   
     
     
         8 . The steel continuous casting method according to  claim 7 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while a direct-current static magnetic field is applied to the molten steel inside the mold, on an upper side of a discharge port located at a vertically uppermost part and on a lower side of a discharge port located at a vertically lowermost part of the immersion nozzle, from a direct-current magnetic field generation device installed on a back surface of the mold for continuous casting. 
     
     
         9 . The steel continuous casting method according to  claim 7 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while an alternating-current moving magnetic field is applied to the molten steel inside the mold from an alternating-current magnetic field generation device installed on a back surface of the mold for continuous casting. 
     
     
         10 . The steel continuous casting method according to  claim 8 , wherein the molten steel inside the tundish is poured into the mold through the immersion nozzle, while an alternating-current moving magnetic field is applied to the molten steel inside the mold from an alternating-current magnetic field generation device installed on the back surface of the mold for continuous casting.