Iron-based sintered alloy material for valve sheet and process for preparing the same

Abstract

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/cm 3 . 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.

What is claimed is:  
     
         1 . 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/cm 3 .  
     
     
         2 . An iron-base sintered alloy material according to  claim 1 , wherein the composition of a base matrix portion consisting of said base matrix phase and said hard particle has a composition containing a total of 10.0 to 40.0% of one or more selected from Ni: 2.0 to 23.0%, Cr: 0.4 to 15.0%, Mo: 3.2 to 15.0%, Cu: 0.2 to 3.0%, Co: 3.0 to 15.0%, V: 0.1 to 0.5%, Mn: 0.1 to 0.5%, W: 0.2 to 6.0%, C: 0.8 to 2.0%, Si: 0.1 to 1.0% and S: 0.1 to 1.0% by mass, and the balance substantially Fe, said hard particle is a particle composed of one or more elements selected from C, Cr, Mo, Co, Si, Ni, S and Fe.  
     
     
         3 . The iron-base sintered alloy material for a valve sheet according to  claim 1  or  2 , wherein a solid lubricant particle is further dispersed in said base matrix phase at 0.3 to 3.5% by area ratio.  
     
     
         4 . The iron-base sintered alloy material according to  claim 3 , wherein said solid lubricant particle is one or more selected from a sulfide and a fluoride.  
     
     
         5 . 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/cm 3  and a porosity by volume ratio of 12 to 25% is obtained.  
     
     
         6 . The process for preparing an iron-base sintered alloy material for a valve sheet according to  claim 5 , wherein a solid lubricant particle powder is further blended into the raw material powder at 0.2 to 3.0 parts by weight relative to 100 parts by weight of a total amount of a raw material powder.  
     
     
         7 . The process for preparing an iron-base sintered alloy material for a valve sheet according to  claim 5  or  6 , wherein in place of a part or all of said alloy iron powder, an alloy element powder of one or more selected from Ni, Cr, Mo, Cu, Co, V, Mn, W and C is blended at a total amount of 0.3 to 15% by weight relative to a total amount of raw material powder.  
     
     
         8 . The process for preparing an iron-base sintered alloy material for a valve sheet according to any one of  claims 5  to  7 , wherein said predetermined green density is 6.2 to 7.0 g/cm 3 .  
     
     
         9 . The process for preparing an iron-base sintered alloy material for a valve sheet according to any one of  claims 5  to  7 , wherein said sintering conditions are conditions of sintering by heating to a temperature range of 1000 to 1200° C.  
     
     
         10 . The process for preparing an iron-base sintered alloy material for a valve sheet according to  claim 8 , wherein said sintering conditions are conditions of sintering by heating to a temperature range of 1000 to 1200° C.  
     
     
         11 . 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 .