A cutting tool whose surface is coated with a composite hard layer formed by chemical vapor deposition and having excellent wear resistance and chipping resistance. The cutting tool contains a substrate whose surface is coated with a composite hard layer containing an inner layer including one or more layers of titanium carbide, titanium nitride, titanium carbonitride, titanium carboxide, and titanium oxicarbonitride, and an outer layer including at least one alumina layer. The alumina layer contains K-type alumina such that an X-ray intensity ratio I.sub.A /I.sub.B of two specific crystal faces A and B in X-ray diffraction is not smaller than 2, where the A-face and B-face denote faces of K-type alumina defined as those whose interfacial distances are 2.79.ANG. and 2.57.ANG. in ASTM4-0878, and I.sub.A and I.sub.B denote X-ray intensity of the faces A and B in X-ray diffraction.
A method of preparing a coated cutting tool is provided involving formation of a hard coating layer including an aluminum oxide layer to an average layer thickness of 3-20 microns on the surface of a cutting tool substrate using chemical vapor deposition and/or physical vapor deposition, to give a coated cutting tool excellent in chipping resistance, where the aluminum oxide layer is formed from an inert gas type reaction gas containing aluminum chloride and nitrogen oxides, and optionally titanium tetrachloride, nitrogen and hydrogen, in an inert carrier gas.
An oxide coated cutting tool including a body coated with refractory single- or multilayers one of which consists of single-phase .kappa.-Al.sub.2 O.sub.3 characterized by controlled microstructure with crystal planes preferably grown in the (210)-direction with respect to the exposed sure of the coated body. The oxide coated cutting tool exhibits increased wear properties when machining ball bearing steel.
An oxide coated cutting tool including a body coated with refractory single- or multilayers one of which consists of single-phase .kappa.-Al.sub.2 O.sub.3 characterized by controlled microstructure with crystal planes preferably grown in the (210)-direction with respect to the exposed surface of the coated body. The oxide coated cutting tool exhibits increased wear properties when machining ball bearing steel.
The present invention discloses a coated cutting insert particularly useful for dry milling of grey cast iron. The insert is characterized by a WC--Co cemented carbide substrate and a coating including an innermost layer of TiC.sub.x N.sub.y O.sub.z with columnar grains and a top coating of a fine grained .alpha.-Al.sub.2 O.sub.3 layer.
The present invention relates to a coated cutting tool insert useful for grooving or severing steel components such as steel or stainless steel tubes and bars. The insert is characterized by WC--Co-based cemented carbide substrate having a highly W-alloyed Co-binder phase and a relatively thin coating including an inner layer of TiC.sub.x N.sub.y O.sub.z with columnar grains followed by a layer of fine grained .kappa.--Al.sub.2 O.sub.3 and a top layer of TiN.
