Molten steel pouring nozzle

A molten steel pouring nozzle, comprising:

• an upper nozzle (20) made of a refractory, having along the center axis thereof an upper bore (21), an upper end portion of said upper nozzle (20) inserted into an opening in a bottom wall of a molten steel receiving vessel;
• a lower nozzle (23) made of a refractory, having along the center axis thereof a lower bore (24) aligning with said upper bore (21), and having, on an upper end portion (25) thereof, a recess (26, 26') for receiving a lower end portion (22) of said upper nozzle (20), said lower bore (24) of said lower nozzle (23) forming a vertical path (27) for molten steel in cooperation with said upper bore (21) of said upper nozzle (20);
• and
• an open air shutoff means (31) for preventing an open air from penetrating through an interface (28, 28') between said lower end portion (22) of said upper nozzle (20) and said recess (26, 26') of said lower nozzle (23) into said vertical path (27) for molten steel, said open air shutoff means comprising:
• a steel shell (32) covering said upper end portion (25) of said lower nozzle (23), said steel shell having, at the center of an upper surface (32a) thereof, an opening (33) having a size slightly larger than that of said recess (26, 26') of said lower nozzle (23), for receiving said lower end portion (22) of said upper nozzle (20), and said steel shell (32) having, on a side surface (32b) thereof, an inert gas feed port (34);
• an annular equalizing chamber (35), provided between said upper end portion (25) of said lower nozzle (23) and said side surface (32b) of said steel shell (32), over the entire circumference of said upper end portion (25) of said lower nozzle (23), said annular equalizing chamber communicating with said inert gas feed nozzle (34) of said steel shell (32);
• and
• a plurality of grooves (36, 36a, 36b, 36c, 36d) formed at prescribed intervals in the circumferential direction of said lower nozzle (23) between an upper end surface (30) of said lower nozzle (23) and said upper surface (32a) of said steel shell (32), said plurality of grooves being directed toward said lower end portion (22) of said upper nozzle (20), one end of each of said plurality of grooves communicating with said annular equalizing chamber (35), and the other end thereof communicating with said recess (26, 26') of said lower nozzle (23).