A molten steel denitrification method, wherein an extremely low nitrogen concentration range is stably reached in a short time without use of a top-blown gas, is a denitrification process wherein CaOandAl.sub.2O.sub.3-containing slag formed by a combination of an Al addition step of adding a metalAl-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel is brought into contact with the Al-containing molten steel to remove nitrogen in the molten steel, in which the molten steel is stirred at a stirring power density of 60 W/t or higher. In the denitrification process, a surface of the molten steel or the slag is subjected to an atmosphere of 1.010.sup.5 Pa or lower. In a steel production method, the obtained molten steel is cast after the components are adjusted.

A spring steel according to the present embodiment has a chemical composition consisting of, in mass %, C: 0.4 to 0.7%, Si: 1.1 to 3.0%, Mn: 0.3 to 1.5%, P: 0.03% or less, S: 0.05% or less, Al: 0.01 to 0.05%, rare earth metal: 0.0001 to 0.002%, N: 0.015%, O or less: 0.0030% or less, Ti: 0.02 to 0.1%, with the balance being Fe and impurities. In the spring steel, the number of oxide inclusions having an equivalent circular diameter of equal to or greater than 5 m is equal to or less than 0.2/mm.sup.2, the oxide inclusions each being one of an Al-based oxide, a complex oxide containing REM, O and Al, and a complex oxysulfide containing REM, O, S, and Al. Further, a maximum value among equivalent circular diameters of the oxide inclusions is equal to or less than 40 m.

A steel consists of, in mass %, C: 0.25 to 0.45%, Si: 0.10 to 0.50%, Mn: 0.40 to 0.70%, P: 0.015% or less, S: 0.005% or less, Cr: 0.80 to 1.50%, Mo: 0.17 to 0.30%, V: 0.24 to 0.40%, Al: 0.005 to 0.100%, N: 0.0300% or less, O: 0.0015% or less, and the balance being Fe and impurities, and satisfies Formula (1) to Formula (4) described in the present specification, wherein: its microstructure is composed of ferrite and pearlite having a total area fraction of 5.0 to 100.0%, and a hard phase having a total area fraction of 0 to 95.0%; a proportion of a total area of CaOCaSMgOAl.sub.2O.sub.3 composite oxides with respect to a total area of oxides in the steel is 30.0% or more; and a number density of oxides having an equivalent circle diameter of 20.0 m or more is 15.0 pieces/mm.sup.2 or less.

Proposed is a technology capable of inexpensively and stably reducing the nitrogen concentration in molten steel within a melting furnace or a refining furnace to a low nitrogen concentration range. Provided is a method for denitrifying molten steel including supplying an oxygen-containing gas and a carbon source carried with a carrier gas to the molten steel charged into a melting furnace or a refining furnace, in which the oxygen-containing gas and the carbon source are simultaneously blown onto the molten steel under a condition that, provided that a triangle XYZ is defined by connecting, in a plan view seen from above, a distal end (point X) of a discharge port of a carbon-source blowpipe; an intersection point (point Y) between an inner wall of the furnace and a line obtained by extending a central axis of a carbon source blowing direction; and a distal end (point Z) of a discharge port of an oxygen-blowing lance, that a point

W is positioned on a side XY that is away from the point X by a distance a length of the side XY, and that an angle) .sub.1() is an angle XZW, an angle .sub.2() of an oxygen-containing-gas blowing direction that is open toward a Y side with respect to a side ZX passing through the distal end (point Z) of the discharge port of the oxygen-blowing lance in the plan view seen from above is a positive value and is the angle .sub.1 or less.