Abstract: Disclosed is an immersion nozzle, which comprises a vertically-extending pipe-shaped straight nozzle body 10 adapted to allow molten steel to pass downwardly from an inlet port 9 provided at an upper end thereof, and a pair of discharge portions each including a respective one of a pair of outlet ports 12 provided in a lower portion of the straight nozzle body 10 in a bilaterally symmetrical arrangement and adapted to discharge molten steel laterally from a lateral side of the straight nozzle body. Each of the discharge portions has an inner surface defining the outlet port 12 and extending parallel to an axis of the outlet port 12 to define a length of the discharge portion at 45 mm or more. A ratio of S1/S2 is in the range of 0.8 to 1.

Abstract: A refractory protective block protects heat exchange means connecting tubes to fins. The refractory protective block has an inside complementary shape corresponding to the surface shape of the heat exchange means and the refractory protective block is provided with recesses into which projections formed on the tubes are fitted and received. A pair of projections formed on the two adjacent tubes in the heat exchange means are arranged so as to confront each other. The refractory protective block has a high durability which does not break even when heat exchange means expand more than the refractory block at the time of the repetition of heating and cooling and which enable the dispersion of strain at the time of the repetition of expansion and contraction.