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AssigneeNippon Piston Ring Co., Ltd.
InventorsKenichi Sato, Arata Kakiuchi, Teruo Takahashi
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An iron-base sintered alloy material for a valve sheet is a material in which a hard particle composed of one or more elements selected from C, Cr, Mo, Co, Si, Ni, S and Fe is dispersed in a base matrix phase, a porosity is 12 to 25% by volume ratio, and a density after sintering is 6.1 to 6.9 g/cm3. Thereby, production of iron oxide at operation of an internal combustion engine is accelerated, and the abrasion resistance is remarkably improved. It is preferable that a base matrix portion containing a base matrix phase and the hard particle has the composition containing a total of 10.0 to 40.0% of one or more selected from Ni, Cr, Mo, Cu, Co, V, Mn, W and C, and the balance substantially Fe. It is preferable that a solid lubricant particle of one or more selected from a sulfide and a fluoride is firther dispersed in a base matrix phase at 0.3 to 3.5% by area ratio.
An iron-base sintered alloy material in which a hard particle is dispersed in a base matrix phase, and which is used for a valve sheet, characterized in that said hard particle is dispersed at 5 to 40% by area ratio, a porosity is 12 to 25% by volume ratio, and a density after sintering is 6.1 to 6.9 g/cm3.
A process for preparing an iron-base sintered alloy material for a valve sheet, which comprises successively performing a molding step of filling into a mold a raw material powder obtained by blending and mixg 20 to 70% of pure iron powder, 10 to 50% of an alloy iron powder containing a total of 3 to 30% of one or more selected from C, Ni, Cr, Mo, Cu, Co, W. V and Mn, and the balance substantially Fe, and 5 to 40% of a hard particle powder composed of one or more elements selected fiom C, Cr, Mo, Co, Si, Ni, S and Fe by mass relative to a total amount of a raw material powder, and adjusting the compressing and molding conditions to compress and mold the raw material powder to obtain a green compact having a predetermined green density, and a sintering step of adjusting the sintering conditions to heat and sinter the green compact in the protective atmosphere to obtain a sintered body, whereby a sintered body having a density after sintering of 6.1 to 6.9 g/cm3 and a porosity by volume ratio of 12 to 25% is obtained.
A valve sheet made of an iron-base sintered alloy, which comprises, as a material, the iron-base sintered alloy material for a valve sheet according to any one of daims 1 to 4.
Dependencies are inferred from the claim text.