Sintered valve seat

1. A sintered valve seat press-fitted into a cylinder head of an internal engine;

said valve seat having a two-layer structure comprising a seat layer repeatedly abutting a valve face, and a support layer abutting bottom and inner peripheral surfaces of a valve-seat-press-fitting opening of a cylinder head;

said seat layer containing at least one selected from Co-based hard particles and Fe-based hard particles in a matrix of Cu or its alloy; and

said support layer containing at least one selected from Fe particles and Fe alloy particles in a matrix of Cu or its alloy.

2. The sintered valve seat according to claim 1 , wherein

said seat layer contains 25-70% by mass of at least one selected from Co-based hard particles and Fe-based hard particles; and

said support layer contains 30-70% by mass of at least one selected from Fe particles and Fe alloy particles.

3. The sintered valve seat according to claim 1 , wherein said support layer has higher thermal conductivity than that of said seat layer.

4. The sintered valve seat according to claim 1 , wherein the volume ratio of said seat layer to said support layer is 25/75-70/30.

5. The sintered valve seat according to claim 1 , wherein

said Co-based hard particles contained in said seat layer are at least one selected from Co—Mo—Cr—Si alloy particles comprising by mass 27.5-30.0% of Mo, 7.5-10.0% of Cr, and 2.0-4.0% of Si, the balance being Co and inevitable impurities, Co—Cr—W—C alloy particles comprising by mass 27.0-32.0% of Cr, 7.5-9.5% of W, and 1.4-1.7% of C, the balance being Co and inevitable impurities, and Co—Cr—W—C alloy particles comprising by mass 28.0-32.0% of Cr, 11.0-13.0% of W, and 2.0-3.0% of C, the balance being Co and inevitable impurities; and

said Fe-based hard particles contained in said seat layer are Fe—Mo—Cr—Si alloy particles comprising by mass 27.5-30.0% of Mo, 7.5-10.0% of Cr, and 2.0-4.0% of Si, the balance being Fe and inevitable impurities.

6. The sintered valve seat according to claim 1 , wherein in said support layer, said Fe particles are Fe particles comprising 96% or more by mass of Fe and inevitable impurities; and said Fe alloy particles are at least one selected from Fe—Cr alloy particles comprising 0.5-3.0% by mass of Cr, the balance being Fe and inevitable impurities, and Fe—Cr—Mo alloy particles comprising by mass 0.5-5.0% of Cr, and 0.1-2.0% of Mo, the balance being Fe and inevitable impurities.

7. The sintered valve seat according to claim 5 , wherein

part of at least one selected from said Co-based hard particles and said Fe-based hard particles, which are contained in said seat layer, are substituted by second hard particles; and

said second hard particles are at least one selected from alloy steel particles comprising by mass 1.4-1.6% of C, 0.4% or less of Si, 0.6% or less of Mn, 11.0-13.0% of Cr, 0.8-1.2% of Mo, and 0.2-3.0% of V, the balance being Fe and inevitable impurities, alloy steel particles comprising by mass 0.35-0.42% of C, 0.8-1.2% of Si, 0.25-0.5% of Mn, 4.8-5.5% of Cr, 1-1.5% of Mo, and 0.8-1.15% of V, the balance being Fe and inevitable impurities, alloy steel particles comprising by mass 0.8-0.88% of C, 0.45% or less of Si, 0.4% or less of Mn, 3.8-4.5% of Cr, 4.7-5.2% of Mo, 5.9-6.7% of W, and 1.7-2.1% of V, the balance being Fe and inevitable impurities, and alloy steel particles comprising by mass 0.01% or less of C, 0.3-5.0% of Cr, and 0.1-2.0% of Mo, the balance being Fe and inevitable impurities.

8. The sintered valve seat according to claim 7 , wherein

part of at least one selected from said Co-based hard particles and said Fe-based hard particles, which are contained in said seat layer, are substituted by third hard particles;

said third hard particles are at least one selected from Fe—Mo—Si alloy particles comprising by mass 40-70% of Mo, and 0.4-2.0% of Si, the balance being Fe and inevitable impurities, Al 2 O 3 particles, and SiC particles.

9. The sintered valve seat according to claim 6 , wherein

part of at least one selected from said Fe particles and said Fe alloy particles, which are contained in said support layer, are substituted by second hard particles; and

said second hard particles are at least one selected from alloy steel particles comprising by mass 1.4-1.6% of C, 0.4% or less of Si, 0.6% or less of Mn, 11.0-13.0% of Cr, 0.8-1.2% of Mo, and 0.2-3.0% of V, the balance being Fe and inevitable impurities, alloy steel particles comprising by mass 0.35-0.42% of C, 0.8-1.2% of Si, 0.25-0.5% of Mn, 4.8-5.5% of Cr, 1-1.5% of Mo, and 0.8-1.15% of V, the balance being Fe and inevitable impurities, and alloy steel particles comprising by mass 0.8-0.88% of C, 0.45% or less of Si, 0.4% or less of Mn, 3.8-4.5% of Cr, 4.7-5.2% of Mo, 5.9-6.7% of W, and 1.7-2.1% of V, the balance being Fe and inevitable impurities.

10. The sintered valve seat according to claim 9 , wherein

part of at least one selected from said Fe particles and said Fe alloy particles, which are contained in said support layer, are substituted by third hard particles; and

said third hard particles are at least one selected from Fe—Mo—Si alloy particles comprising by mass 40-70% of Mo, and 0.4-2.0% of Si, the balance being Fe and inevitable impurities, Al 2 O 3 particles, and SiC particles.

11. The sintered valve seat according to claim 1 , wherein said seat layer contains 0.05-2.2% by mass of P.

12. The sintered valve seat according to claim 1 , wherein said support layer contains 0.1-2.2% by mass of P.

13. The sintered valve seat according to claim 1 , wherein said seat layer contains up to 6.5% by mass of Sn.

14. The sintered valve seat according to claim 1 , wherein said seat layer contains up to 3% by mass of a solid lubricant.

15. The sintered valve seat according to claim 14 , wherein said solid lubricant is at least one selected from the group consisting of C, BN, MnS, CaF 2 , SiO 2 , WS 2 and Mo 2 S.