Patent ID: 7510761

Claim:
A cutting tool made of surface-coated cemented carbide having a hard coating layer that exhibits excellent wear resistance in high speed cuffing operation of high hardness steel, comprising: a carbide substrate made of tungsten-carbide cemented carbide or titanium-carbonitride cermet and the hard coating layer formed on the surface of the carbide substrate by vapor deposition, wherein (a) the hard coating layer includes a top layer and a bottom layer both formed from composite nitride of Ti, Al and Si, the top layer having the thickness in a range from 0.5 to 1.5 Î¼m and the bottom layer having the thickness in a range from 2 to 6 Î¼m; (b) the top layer includes a structure having the thin layer A and the thin layer B stacked alternately each having the thickness of 5 to 20 nm, with the thin layer A comprising composite nitride of Ti, Al and Si having the composition of [Ti 1âˆ’(A+B) Al A Si B ]N (A is in a range from 0.01 to 0.06 and B is in a range from 0.25 to 0.35 in an atomic ratio) and the thin layer B comprising composite nitride of Ti, Al and Si having the composition of [Ti 1âˆ’(C+D) Al C Si D ]N (C is in a range from 0.30 to 0.45 and D is in a range from 0.10 to 0.15 in an atomic ratio); and (c) the bottom layer comprising composite nitride of Ti, Al and Si of single phase structure having the composition of [Ti 1âˆ’(E+F) Al E Si F ]N (E is in a range from 0.50 to 0.60 and F is in a range from 0.01 to 0.09 in an atomic ratio).