Control method for producing ultra-low carbon steel through small square billet continuous casting

The invention discloses a control method for producing ultra-low carbon steel through continuous casting of small square billets, which comprises the following control conditions: 1) after molten steel is subjected to vacuum treatment by an RH furnace, oxygenation of the molten steel in a tundish is controlled, and the oxygen content of the molten steel in the tundish is 50-90ppm; (2) during continuous casting, an integral submersed nozzle made of a zirconium carbon material is adopted, and the inner diameter of the nozzle ranges from 40 mm to 45 mm; 3) controlling the carbon content at the slag line of the integral submersed nozzle to be 6.5-8.5%; (4) the baking temperature of the whole submersed nozzle is controlled between 1050 DEG C and 1100 DEG C; and (5) the carbon content in the crystallizer casting powder is controlled to range from 1.0% to 2.0%. The castability of ultra-low carbon steel produced through small square billet continuous casting is improved, the service life of a single tundish is prolon