Method of preparing coated cemented carbide product

Method of treating a cemented carbide substrate containing at least one carbide together with binder metal in order to improve its wear resistance and utility, which method consists essentially of the sequential steps of:

• (a) treating the substrate in an atmosphere selected from carbide, nitride and carbonitride forming atmospheres to form or apply a coating essentially comprising at least one coat of at least one member selected from the group consisting of carbides, nitrides and carbonitrides of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and B;
• (b) heat treating the coated substrate at a temperature close to or greater than the melting point of the binder phase in order to diffuse elements from the substrate into said coating and from the coating into the substrate and to form a microrough surface on the substrate, the treatment of the substrate according to steps (a) and (b) above being performed as one operation, in which the member of the metals of the substrate forming the carbide, nitride and carbonitride is brought to diffuse from the interior of the substrate out to the surface;
• (c) treating the substrate from step (b) in an atmosphere selected from carbide, nitride and carbonitride forming atmospheres to form or apply a second coating essentially comprising at least one member selected from the group consisting of carbides, nitrides and carbonitrides of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and B;
• (d) treating the resulting substrate with a nitrogen-containing gas to nitride a portion of the second coating without detrimentally effecting the adherence of the second coating to the said substrate;
• and
• (e) applying a wear resistant oxide coating on the thus pretreated cemented carbide substrate.