NITRIDING TREATMENT FOR METAL

PURPOSE:To obtain a nitrided layer free from the formation of oxide film and having sufficiently high hardness by adding Mn, Cr, Si, B, Ti, V, Mo, Co, Hf, Nb, Sb, etc., to a molten metal stock and then applying nitriding treatment to the above. CONSTITUTION:In the course of the melting of a metal stock, one or more additives among Mn, Cr, Si, B, Ti, V, Mo, Co, Hf, Nb, and Sb are added to undergo mixing and agitation. Suitable additive quantities are, e.g. about 1.0-2.0% Mn, about 0.05-2.0% Cr, about 1.0-4.0% Si, and about 0.01-1.0% B, and it is desirable that they are added in the form of ferroalloy, such as Fe-Mn. Further, besides the above additives, one or more kinds among Ca-Si, Fe-Si, Fe-Mg, and Ni-Mg may be added as inoculants. Then, the metal stock into which the additives, etc., are mixed is subjected to nitriding treatment, such as plasma nitriding and soft nitriding. By this method, nitriding reaction can be selectively accelerated and the formation of oxide film can be perfectly prevented, by which the nitrided layer having high hardness and excellent in wear resistance and scuffing resistance can be formed.