Surface-coated cutting tool having therein hard coating layer capable of exhibiting excellent chipping resistance during high-speed intermittent cutting work

A surface-coated cutting tool comprising:

• a cutting tool body made of any one of cemented carbide including tungsten carbide, cermet including titanium carbonitride, and ultra-high pressure sintered material including cubic boron nitride;
• and
• a hard coating layer coated on a surface of the cutting tool body, wherein
• (a) the hard coating layer comprises at least a complex carbonitride layer of Ti and Al with a cubic crystal structure, the complex carbonitride layer being vapor-deposited by a chemical vapor deposition method and having an average thickness of 1-20 μm,
• (b) an Al content ratio X and a C content ratio Y satisfy 0.60≦X≦0.90 and 0.0005%≦Y≦0.005, respectively, in the complex carbonitride layer:
• an average composition of the complex carbonitride layer being expressed by a composition formula, (Ti1-XAlX)(CYN1-Y);
• and X and Y being in atomic ratio,
• (c) an Al content ratio XL is 0.55≦XL≦0.70:
• a location L being a location 0.3 μm from an interface of the complex carbonitride layer on a side of the cutting tool body to an internal part of the complex carbonitride layer;
• compositional analysis being performed on a cross-section, which includes the location L and is perpendicular to the surface of the cutting tool body, centering around the location L to obtain an Al content ratio of the complex carbonitride layer of Ti and Al with a cubic crystal structure;
• and the Al content ratio XL being calculated as an average value of the obtained Al content ratio by the compositional analysis in atomic ratio;
• an Al content ratio XH is 0.8≦XH≦0.95:
• a location H being a location 0.3 μm from an interface of the complex carbonitride layer on an outer surface side of the complex carbonitride layer to the internal part of the complex carbonitride layer;
• compositional analysis being performed on a cross-section, which includes the location H and is perpendicular to the surface of the cutting tool body, centering around the location H to obtain an Al content ratio of the complex carbonitride layer of Ti and Al with a cubic crystal structure;
• and the Al content ratio XH being calculated as an average value of the obtained Al content ratio by the compositional analysis in atomic ratio;
• and
• the complex carbonitride layer has a compositionally gradient structure in which the Al content ratio in the complex carbonitride layer gradually increases from the interface of the complex carbonitride layer on the side of the cutting tool body to the outer surface side of the complex carbonitride layer, and
• (d) an average grain size DL, which is an average value of crystal grain width of the complex carbonitride in a cross-section including the location L and being parallel to the surface of the cutting tool body, is 0.1 μm or less;
• an average grain size DH, which is an average value of crystal grain width of the complex carbonitride in a cross-section including the location H and being parallel to the surface of the cutting tool body, is 0.5 μm to 2 μm;
• and
• an average grain size of the complex carbonitride layer of Ti and Al with the cubic crystal structure forms a grain size distribution gradually increasing from the interface of the complex carbonitride layer on the side of the cutting tool body to the outer surface side of the complex nitride layer.