Sintered alloy valve guide and its production method

Abstract

To provide a sintered alloy valve guide having high thermal conductivity and excellent wear resistance, which can be used in engines subjected to a large thermal load due to downsizing, direct injection and supercharging, the sintered alloy has a composition comprising by mass 10-90% of Cu, 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-3% of C, the balance being substantially Fe and inevitable impurities, the total amount of Cr, Mo, V and W being 2% or more, and a structure comprising an Fe-based alloy phase, a Cu or Cu-based alloy phase, and a graphite phase.

1 . A sintered alloy valve guide having a composition comprising by mass 10-90% of Cu, 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-3% of C, the balance being substantially Fe and inevitable impurities, the total amount of Cr, Mo, V and W being 2% or more, and having a structure comprising an Fe-based alloy phase, a Cu or Cu-based alloy phase, and a graphite phase. 
     
     
         2 . The sintered alloy valve guide according to  claim 1 , wherein said Fe-based alloy phase is an Fe—Mo—C alloy, an Fe—Cr—Mo—V—C alloy, an Fe—Cr—V—W—C alloy, or an Fe—Cr—Mo—V—W—C alloy. 
     
     
         3 . The sintered alloy valve guide according to  claim 2 , wherein said Fe-based alloy phase has a composition comprising by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-1% of C, the balance being substantially Fe and inevitable impurities, the total amount of Cr, Mo, V and W being 2% or more. 
     
     
         4 . The sintered alloy valve guide according to  claim 1 , wherein said Cu or Cu-based alloy phase is continuous in the structure. 
     
     
         5 . The sintered alloy valve guide according to  claim 4 , wherein said Cu or Cu-based alloy phase has thermal conductivity of 200 W/mK or more. 
     
     
         6 . A method for producing a sintered alloy valve guide comprising the steps of coating prealloy powder having a composition comprising by mass 0-10% of Cr, 0-6% of Mo, 0-8% of V, 0-8% of W, and 0.5-1% of C, the balance being substantially Fe and inevitable impurities, the total amount of Cr, Mo, V and W being 2% or more, with Cu, mixing the Cu-coated prealloy powder with C powder, and then molding and sintering.