MOLTEN STEEL DENITRIFICATION METHOD AND STEEL PRODUCTION METHOD

A molten steel denitrification method including CaO-and-Al2O3-containing slag is formed by adding a metal-Al-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and adding a CaO-containing substance to the molten steel, and then an oxygen-containing gas is blown from above the slag to perform a denitrification treatment. T·Fe in the slag after the denitrification treatment is set to 3.0 mass % or lower. It is preferable that, in the denitrification treatment, the oxygen-containing gas be supplied such that a ratio Ls/Ls0 between a thickness Ls0 of the slag and a depth Ls of a depression in the slag resulting from blowing of the oxygen-containing gas becomes 0.9 or lower. The obtained molten steel is cast after its components are adjusted. The method allows an extremely low nitrogen concentration range to be stably reached in a short time.