CEMENTED CARBIDE COATED CUTTING TOOL INSERT PARTICULARLY USEFUL IN TURNING OF CAST IRON AS WELL AS LOW ALLOY STEEL AT MIDIUM TO HIGH CUTTING SPEED

摘要

PURPOSE: To provide a coated cutting tool insert that shows excellent performance in turning of cast iron and low alloy steel. CONSTITUTION: The coated cutting tool insert comprises a cemented carbide body and a coating and is particularly useful in turning of cast iron and low alloy steel, wherein the cemented carbide body has a composition comprising 3.0 to 8.0 wt.%, preferably 4.5 to 7.0 wt.% of Co, 0.5 to 4.0 wt.%, preferably 1.0 to 4.0 wt.% of cubic carbonitride forming elements selected from groups IVb and Vb of the periodic table and the balance being N, C and WC and has a surface region of which thickness is 5 to 40 m, preferably 10 to 30 m, and on which a binder phase is enriched, but a cubic carbonitride phase hardly exists, the maximum content of the binder phase on the surface region being 1.2 to 3 by volume of content of a bulk binder phase; and the coating comprises a first innermost layer of TiCxNyOz (where 0.7=x+y+z=1, preferably z0.5, more preferably yx, and z0.2, most preferably y0.7, grains being equiaxed grains, and the total thickness being less than 2 m, preferably exceeding 0.1 m), a TiCxNyOz layer (where 0.7=x+y+z=1, preferably z0.2, x0.3, and y0.2, most preferably x0.4, thickness being 3 to 14 m, preferably 4 to 12 m, most preferably 5 to 10 m, and grains being columnar grains), and at least one Al2O3 layer (where thickness being 2 to 14 m, preferably 3 to 10 m).