Abstract: In an end mill body made of ceramic, a corner R rake face is formed in such a manner as to contain a point B and at least a region B, not a region A located on a side toward an end cutting edge. In other words, a first end portion of a cutting edge on a peripheral edge portion of the corner R rake face is formed on a peripheral edge of the region B of a corner R cutting edge, and a second end portion of the cutting edge reaches at least the point B. As a result, partial breakage of the corner R cutting edge is unlikely to occur in the course of cutting. That is, since the corner R rake face is formed in such a manner as to start from the first end portion located apart from a point A, which is the intersection of the end cutting edge and the corner R cutting edge, and such that the second end portion reaches the point B, a large cutting load is unlikely to be imposed on the starting point of the corner R rake face. Therefore, the corner R cutting edge is unlikely to be chipped.

Abstract: In an end mill body made of ceramic, a corner R rake face is formed in such a manner as to contain a point B and at least a region B, not a region A located on a side toward an end cutting edge. In other words, a first end portion of a cutting edge on a peripheral edge portion of the corner R rake face is formed on a peripheral edge of the region B of a corner R cutting edge, and a second end portion of the cutting edge reaches at least the point B. As a result, partial breakage of the corner R cutting edge is unlikely to occur in the course of cutting. That is, since the corner R rake face is formed in such a manner as to start from the first end portion located apart from a point A, which is the intersection of the end cutting edge and the corner R cutting edge, and such that the second end portion reaches the point B, a large cutting load is unlikely to be imposed on the starting point of the corner R rake face. Therefore, the corner R cutting edge is unlikely to be chipped.

Abstract: An insert includes a silicon nitride sintered body including ?-Si3N4 as a main component, Mg, and a rare-earth element Re (Y, La, Ce, Er, Dy, Yb). A content of Mg in terms of MgO is 1.0-7.0 mol %, a content of Re in terms of an oxide thereof is 0.4-1.0 mol %, and a total content of Mg and Re is from 1.7 to less than 7.5 mol %. The insert has a graded composition in which oxygen content increases from a surface of the sintered body toward an inside thereof such that 0.8-1.5 mass % of oxygen is contained in a region of less than 0.5 mm inside from the surface, 1.1-2.3 mass % of oxygen is contained in a region of 0.5 mm or more inside from the surface, and a difference in oxygen content between the regions is 0.1-1.0 mass %.

Abstract: An insert includes a silicon nitride sintered body including ?-Si3N4 as a main component, Mg, and a rare-earth element Re (Y, La, Ce, Er, Dy, Yb). A content of Mg in terms of MgO is 1.0-7.0 mol %, a content of Re in terms of an oxide thereof is 0.4-1.0 mol %, and a total content of Mg and Re is from 1.7 to less than 7.5 mol %. The insert has a graded composition in which oxygen content increases from a surface of the sintered body toward an inside thereof such that 0.8-1.5 mass % of oxygen is contained in a region of less than 0.5 mm inside from the surface, 1.1-2.3 mass % of oxygen is contained in a region of 0.5 mm or more inside from the surface, and a difference in oxygen content between the regions is 0.1-1.0 mass %.

Abstract: A ceramic cutting tool including a ceramic base member 4 of a tool main body 1 which is formed of a composite ceramic which contains a hard phase dispersed within an alumina matrix phase. The hard phase contains, as a predominant component, one or more elements selected from hard-phase-forming metal elements M in the form of at least one of a carbide, nitride, or boride, or in the form of a solid solution of at least two selected from the carbide, nitride and boride. The hard-phase-forming metal elements M include Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si. The surface of the ceramic base member 4 is covered with a coating layer 1f, which contains titanium carbonitride or titanium nitride as a predominant component. The coating layer 1f has an average crystal-grain size of 0.1 to 0.5 ?m as observed on the surface, and an average thickness of 0.5 to 2 ?m. The coating layer 4f is formed by a CVD at a low to medium temperature range of 750 to 900° C.

Abstract: An alumina-based composite sintered material comprising alumina as a main ingredient and containing one or more carbonitridation products of groups IVa, Va and VIa of the periodic table and/or two or more carbonitridation products of solid solutions of groups IVa, Va and VIa of the periodic table. The content of nitrogen solid solute in the carbonitridation product increases from the interior to the surface of the sintered material, and the Vickers hardness at the surface of the sintered material is 19.5 GPa or more.

Abstract: A ceramic cutting tool including a ceramic base member 4 of a tool main body 1 which is formed of a composite ceramic which contains a hard phase dispersed within an alumina matrix phase. The hard phase contains, as a predominant component, one or more elements selected from hard-phase-forming metal elements M in the form of at least one of a carbide, nitride, or boride, or in the form of a solid solution of at least two selected from the carbide, nitride and boride. The hard-phase-forming metal elements M include Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si. The surface of the ceramic base member 4 is covered with a coating layer 1f, which contains titanium carbonitride or titanium nitride as a predominant component. The coating layer 1f has an average crystal-grain size of 0.1 to 0.5 &mgr;m as observed on the surface, and an average thickness of 0.5 to 2 &mgr;m. The coating layer 4f is formed by a CVD at a low to medium temperature range of 750 to 900° C.

Abstract: An alumina-based composite sintered material comprising alumina as a main ingredient and containing one or more carbonitridation products of groups IVa, Va and VIa of the periodic table and/or two or more carbonitridation products of solid solutions of groups IVa, Va and VIa of the periodic table. The content of nitrogen solid solute in the carbonitridation product increases from the interior to the surface of the sintered material, and the Vickers hardness at the surface of the sintered material is 19.5 GPa or more.