Method of refining molten metal

A method of refining molten metal, which method comprises refining a molten metal in a vessel having heating means under a reduced pressure of vacuum or a low oxygen partial pressure atmosphere to reduce its nitrogen content to 0.01% or less, adding a flux into the refined molten metal substantially without slag, and subsequently heating the molten metal by means of inert gas plasma to re-refine the refined molten metal.

A method of refining molten metal, wherein oxygen or a mixture of oxygen and an insert gas is added or blown into a previously molten metal to reduce its carbon content to 0.01% or less, the processed molten metal is transferred to a vessel having heating means and subjected to reduced-pressure-refining, a flux is added into the molten metal after the reduced-pressure-refining and subsequently the molten metal and flux is heated by means of inert gas plasma to re-refine the metal to reduce its carbon content to 0.01% or less.

A method of refining molten metal, wherein oxygen or a mixture of oxygen and an inert gas is added or blown into a molten metal in vessel having heating means to adjust carbon content of the metal to 0.01% or less, the processed molten metal is subjected to reduced-pressure-refining, a flux is added into the molten metal after the reduced-pressure-refining, and subsequently the molten metal is heated by means of inert gas plasma to re-refine the metal to reduce its carbon content to 0.01% or less.

A method of refining molten metal, wherein a flux mainly comprising any combination of CaO and CaF.sub.2, CaO and Al.sub.2 O.sub.3, or CaO, CaF.sub.2 and Al.sub.2 O.sub.3 is added into a molten metal which has been previously subjected to a reduced-pressure-refining in a vessel having heating means, and subsequently the molten metal is heated by means of inert gas plasma to re-refine the molten metal to reduce its sulfur content to 0.005% or less.

A method of refining molten metal, wherein a previously melted Fe--Ni system alloy comprising 30 to 50 wt % Ni is poured into a vessel having heating means, the molten metal is subjected to a reduced-pressure-refining to reduce its carbon content to 0.01% or less, a flux mainly comprising any combination of CaO and CaF.sub.2, CaO and Al.sub.2 O.sub.3, or CaO, CaF.sub.2 and Al.sub.2 O.sub.3 is added into the refined molten metal, and subsequently the resultant refined molten metal is heated by means of inert gas plasma to re-refine the metal to reduce its carbon and sulfur contents to 0.01% or less and 0.005% or less, respectively.

A method of refining molten metal, wherein a previously melted Fe--Ni system alloy comprising 30 to 50 wt % Ni is melted from a starting cold material in a vessel having heating means under vacuum or a low oxygen partial pressure atmosphere and subjected to reduced pressure refining, a flux mainly comprising any combination of CaO and CaF.sub.2, CaO and Al.sub.2 O.sub.3, or CaO, CaF.sub.2 and Al.sub.2 O.sub.3 is added into the refined molten metal, and subsequently the refined molten metal is heated by means of inert gas plasma to re-refine it to reduce its carbon and sulfur contents to 0.01% or less and 0.005% or less, respectively.