To reduce N content in a steel without providing any new equipment by adding a specific solid oxygen source into molten metal in a vacuum refining.
At the time of executing the vacuum rerfining by using a vacuum refining furnace into which Ar gas is blown from the lower side, the solid oxygen source is added into the refining molten metal. The refining molten metal is a permalloy or a high speed tool steel. As the solid oxidizing source, one or more kinds among Fe2O3, MoO3, NiO3 and Si2O are selected. By this method, the N content can be reduced without modifying the conventional refining method. As the method for adding the solid oxidizing source, the method for placing the source on the bottom of the vacuum refining furnace before pouring the molten metal, the method for blowing the source into the molten metal through a lance and the method for pushing the source into the molten metal by being contained in a refractory-made vessel are exemplified, but the method for placing the source on the bottom of the vacuum refining furnace is simple and reliable.
ISAKA TAKESHI
SAKUMA HITOSHI
