Aluminum pellets are ejected from the nozzle of an elongated tube into a stream of liquid steel flowing from a tundish into a continuous casting mold. Protective gas is utilized to propel the pellets of aluminum from the elongated tube into the molten stream. A special nozzle structure for the elongated tube insures that the aluminum pellets will properly impinge upon and mix with the molten stream. The elongated tube is retained within a larger cylindrical tube that directs low velocity, protective gas at the molten stream. The protective gas, such as nitrogen or argon, provides essentially nonreactive atmosphere that envelops the molten stream of steel.