Sintered valve seat and production method therefor

1. A sintered valve seat comprising:

a matrix;

5 to 40 mass % of hard phase dispersed in the matrix, the hard phase containing: 48 to 60 mass % of Mo; 3 to 12 mass % of Cr; 1 to 5 mass % of Si; and the balance of Co and inevitable impurities; and

a structure in which Cr sulfides are dispersed around the hard phase, wherein the hard phase is formed with a Co base alloy matrix and compounds which are mainly composed of Mo silicides and are integrally precipitated in the Co base alloy matrix.

2. A sintered valve seat according to claim 1 , wherein the sintered valve seat contains 0.04 to 5 mass % of S.

3. A sintered valve seat according to claim 1 , wherein the sintered valve seat further comprises:

5 to 20 mass % of lubricant phase dispersed in the matrix and containing 4 to 25 mass % of Cr,

wherein the lubricant phase is formed such that Cr sulfide particles are precipitated and gathered in a Fe—Cr based alloy matrix.

4. A sintered valve seat according to 3 , wherein the sintered valve seat further includes carbides dispersed in the lubricant phase.

5. A sintered valve seat according to claim 1 , wherein the sintered valve seat has pores, powder boundaries, and a metal structure which is formed in the pores and between the powder boundaries and in which 2 mass % or less of at least one selected from the group consisting of manganese sulfide particles, calcium fluoride particles, boron nitride particles, magnesium silicate mineral particles, bismuth particles, and bismuth oxide particles is dispersed.

6. A sintered valve seat according to claim 1 , wherein the sintered valve seat has pores, and one selected from the group consisting of lead, lead alloy, copper, copper alloy, and aclylic resin is filled in the pores.

7. A production method for a sintered valve seat, comprising:

preparing a matrix forming steel powder composed of at least one of steel powders (B) to (E), a hard phase forming powder (F), a graphite powder, and a sulfide powder composed of at least one of sulfide powders (G) to (J);

mixing a raw powder composed of the matrix forming steel powder, 5 to 40 mass % of the hard phase forming powder (F), 0.4 to 1.2 mass % of the graphite powder, and the sulfide powder of which S content in the raw powder is 0.04 to 5 mass %;

compacting the raw powder into a green compact having a desired shape; and

sintering the green compact into a sintered compact,

wherein

the steel powder (B) is a steel powder containing: 2 to 4 mass % of Cr; 0.2 to 0.4 mass % of Mo; 0.2 to 0.4 mass % of V; and the balance of Fe and inevitable impurities,

the steel powder (C) is a steel powder containing: 5.5 to 7.5 mass % of Co; 0.5 to 3 mass % of Mo; 0.1 to 3 mass % of Ni; and the balance of Fe and inevitable impurities,

the steel powder (D) is a steel powder containing: 0.4 to 4 mass % of Mo; 0.6 to 5 mass % of Ni; 0.5 to 5 mass % of Cu; 0.05 to 2 mass % of Cr; 0.05 to 0.6 mass % of V; and the balance of Fe and inevitable impurities, and

the steel powder (E) is a partial diffusion steel powder containing: 1 to 10 mass % of Ni; 1 to 3 mass % of Cu; 0.4 to 1.0 mass % of Mo; and the balance of Fe and inevitable impurities,

the hard phase forming powder (F) is a Co base alloy powder containing: 48 to 60 mass % of Mo; 3 to 12 mass % of Cr; 1 to 5 mass % of Si; and the balance of Co and inevitable impurities, and

the sulfide powder (G) is a molybdenum disulfide powder, the sulfide powder (H) is a tungsten disulfide powder, the sulfide powder (I) is an iron sulfide powder, and the sulfide powder (J) is a copper sulfide powder.

8. A production method for a sintered valve seat according to claim 7 , wherein the raw powder further includes 5 mass % or less of Ni powder.

9. A production method for a sintered valve seat according to claim 7 ,

wherein the raw powder further contains 5 mass % or less of Cu powder.

10. A production method for a sintered valve seat according to claim 7 , wherein the raw powder further contains 5 to 20 mass % of Cr included steel powder as a lubricant phase forming powder, the Cr included steel powder containing 4 to 25 mass % of Cr.

11. A production method for a sintered valve seat according to claim 10 , wherein

the Cr included steel powder is composed of at least one selected from the group consisting of Cr included steel powders (L) to (Q),

wherein the Cr included steel powder (L) is a Cr included steel powder containing: 4 to 25 mass % of Cr; and the balance of Fe and inevitable impurities,

the Cr included steel powder (M) is a Cr included steel powder containing: 4 to 25 mass % of Cr; 3.5 to 22 mass % of Ni ;and the balance of Fe and inevitable impurities,

the Cr included steel powder (N) is a Cr included steel powder containing: 4 to 25 mass % of Cr; at least one selected from the group consisting of 0.3 to 7 mass % of Mo, 1 to 4 mass % of Cu, 0.1 to 5 mass % of Al, 0.3 mass % or less of N, 5.5 to 10 mass % of Mn, 0.15 to 5 mass % of Si, 0.45 mass % or less of Nb, 0.2 mass % or less of P, 0.15 mass % or less of S, and 0.15 mass % or less of Se; and the balance of Fe and inevitable impurities,

the Cr included steel powder (O) is a Cr included steel powder containing: 4 to 25 mass % of Cr; 3.5 to 22 mass % of Ni; at least one selected from the group consisting of 0.3 to 7 mass % of Mo, 1 to 4 mass % of Cu, 0.1 to 5 mass % of Al, 0.3 mass % or less of N, 5.5 to 10 mass % of Mn, 0.15 to 5 mass % of Si, 0.45 mass % or less of Nb, 0.2 mass % or less of P, 0.15 mass % or less of S, and 0.15 mass % or less of Se; and the balance of Fe and inevitable impurities,

the Cr included steel powder (P) is a Cr included steel powder containing: 7.5 to 25 mass % of Cr; 0.3 to 3.0 mass % of Mo; 0.25 to 2.4 mass % of C; at least one of 0.2 to 2.2 mass % of V and 1.0 to 5.0 mass % of W; and the balance of Fe and inevitable impurities, and the Cr included steel powder (Q) is a Cr included steel powder containing: 4 to 6 mass % of Cr; 4 to 8 mass % of Mo; 0.5 to 3 mass % of V; 4 to 8 mass % of W; 0.6 to 1.2 mass % of C; and the balance of Fe and inevitable impurities.

12. A production method for a sintered valve seat according to claim 7 , wherein the raw powder contains 2 mass % or less of at least one selected from the group consisting of manganese sulfide powder, calcium fluoride powder, boron nitride powder, magnesium silicate mineral powder, bismuth powder, and bismuth oxide powder.

13. A production method for a sintered valve seat according to claim 7 , wherein the production method further comprises:

impregnating or infiltrating a material into pores of the sintered compact after the sintering, the material selected from the group consisting of lead, lead alloy, copper, copper alloy, and aclylic resin.