Sintered valve seat insert and method of manufacture thereof

1. A powder admixture useful for making a sintered valve seat insert, the powder admixture consisting of a first iron-base powder in an amount of 40-60 wt. %, a second iron-base powder in an amount of 20-40 wt. %, up to 20% Fe powder, up to 3% Cu powder, up to 2% MnS powder, and up to 2% die lubricant, wherein the first iron-base powder has a higher hardness than the second iron-base powder, the first iron-base powder consisting of, in weight percent, 1-2% C, 10-25% Cr, 5-20% Mo, 15-25% Co, 30-60 wt. % Fe, up to 1% Mn, up to 1% Si, up to 5% Ni, up to 5% W, up to 2% V, up to 0.5% B, up to 0.1% P, up to 0.1% S, up to 0.5% N, and up to 5% Nb, and the second iron-base powder consisting of, in weight %, 1-1.5% C, 3-15% Cr, 5-7% Mo, 3-6% W, 1-1.7% V, 60-85% Fe, up to 1% Mn, up to 1% Si, optional Ni, optional Co, and optional Nb.

2. The powder admixture of claim 1 , wherein the first iron-base powder has a microstructure of interdendritic and intradendritic phases with up to 25% sigma phase.

3. The powder admixture of claim 1 , wherein the powder admixture includes Fe powder, Cu powder and MnS powder, the first iron-based powder is present in an amount of 40-60 wt. %, the second iron-based powder is present in an amount of 20-40 wt. %, the Fe powder is present in an amount of 15-20 wt. %, the Cu powder is present in an amount of 1-3%, and the MnS powder is present in an amount of 0.1-1 wt. %.

4. The powder admixture of claim 1 , free of additive silicide, carbide, nitride, carbonitride and intermetallic hard powder particles.

5. The powder admixture of claim 1 , wherein the first iron-base powder has a microstructure consisting of 40-60 vol. % interdendritic and 60-40 vol. % intradendritic regions.

6. The powder admixture of claim 1 , free of Co-base, Mo-base, or other hard particle powders having a hardness greater than the hardness of the first iron-base powder.

7. A sintered valve seat inert comprising the powder admixture of claim 1 , wherein the powder admixture has been compacted in the shape of a valve seat insert, sintered to form a sintered powder admixture optionally infiltrated with copper.

8. The sintered valve seat insert of claim 7 , wherein the sintered powder admixture has a density of at least 7.5 g/cm 3 .

9. The sintered valve seat insert of claim 7 , wherein the first iron-base powder has a microstructure consisting of 40-60 vol. % interdendritic and 60-40 vol. % intradendritic regions.

10. The sintered valve seat insert of claim 7 , wherein the sintered admixture is free of hard particle powders having a hardness greater than the hardness of the first iron-base powder.

11. The sintered valve seat insert of claim 7 , wherein the sintered admixture is free of additive silicide, carbide, nitride, carbonitride, Mo-base, Co-base or intermetallic hard particle powders.

12. The sintered valve seat insert of claim 7 , wherein the first iron-based powder is present in an amount of 40-60 wt. %, the second iron-based powder is present in an amount of 20-40 wt. %, and Fe powder is present in an amount of 15-20 wt. %.

13. The sintered valve seat insert of claim 7 , wherein the first iron-based powder is present in an amount of 40-60 wt. %, the second iron-based powder is present in an amount of 20-40 wt. %, Fe powder is present in an amount of 15-20 wt. % and copper is present in an amount of 10-15 wt. %.

14. A method of manufacturing the sintered valve seat insert of claim 7 , comprising forming an admixture by mixing the first iron-based powder with the second iron-based powder, compacting the admixture, and sintering the admixture.

15. The method of claim 14 , wherein the sintering comprises preheating the powder admixture at 560° C., 850° C., and 950° C. for 16 minutes followed by 1120° C. sintering for 48 minutes.

16. The method of claim 14 , wherein (a) the sintering comprises a pressing and sintering process; (b) the method further comprising subjecting the sintered valve seat insert to cryogenic treatment in liquid nitrogen; (c) the method further comprising subjecting the sintered valve seat insert to a steam treatment; and/or (e) the sintering is carried out while infiltrating the admixture with copper.