Insert and cutting tool
An insert includes a silicon nitride sintered body including β-Si 3 N 4 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 %.
1. An insert comprising:
a silicon nitride sintered body, including
β-Si 3 N 4 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 being 1.0-7.0 mol %, a content of Re in terms of an oxide thereof being 0.4-1.0 mol %, and a total content of Mg and Re being from 1.7 to less than 7.5 mol %,
wherein 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 %.
2. The insert as set forth in claim 1 ,
wherein the rare-earth element Re is Yb, and
wherein the content of Mg in terms of MgO is 1.0-5.5 mol %, a content of Yb in terms of Yb 2 O 3 is 0.4-1.0 mol %, and a total content of Mg and Yb is from 1.7 to less than 6.0 mol %.
3. The insert as set forth in claim 1 , wherein a thermal conductivity at room temperature is 45 W/m·K or more in an outer region with a depth of less than 1.0 mm from a surface and 40 W/m·K or more in an inner region with a depth of 1.0 mm or more from the surface.
4. The insert as set forth in claim 1 , wherein a bending strength at room temperature (a three-point bending strength: JIS R1601) is 900 MPa or more.
5. The insert as set forth in claim 1 , wherein crystals containing a Yb element, an Mg element, an Si element, an O element, and an N element are included in a grain boundary phase.
6. The insert as set forth in claim 5 , wherein an intensity (IYb) of a peak indicating a maximum intensity among peaks based on YbMgSi 2 O 5 N in the crystals is more than 0% to equal to 10% or less against an intensity (Is) of a peak indicating a maximum intensity among peaks based on silicon nitride or sialon in an X-ray diffraction chart of the insert of the silicon nitride sintered body.
7. A cutting tool comprising:
a holder; and
an insert attached to the holder, the insert including:
β-Si 3 N 4 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 being 1.0-7.0 mol %, a content of Re in terms of an oxide thereof being 0.4-1.0 mol %, and a total content of Mg and Re being from 1.7 to less than 7.5 mol %,
wherein 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%.