Sintered valve guide and method for producing same
A sintered valve guide having a metallic structure that has a matrix composed of a martensite phase dispersed in a pearlite single phase structure or a mixed structure of ferrite and pearlite, and a pore dispersed within the matrix, wherein the martensite phase exists in a proportion such that an area ratio of the martensite phase in a structure cross-section is within a range from 1 to 10% of the matrix is provided. A method for producing a sintered valve guide is provided, the method includes preparing a mixed powder by adding a copper-phosphorous alloy powder, a nickel powder and a graphite powder to an iron powder, molding the mixed powder into a molded body having a density of 6.8 to 7.2 Mg/m 3 , and sintering the obtained molded body at a temperature of 950 to 1,200° C.
1. A sintered valve guide having a metallic structure that has a matrix composed of a martensite phase dispersed in a mixed structure of ferrite and pearlite, and pores dispersed within the matrix,
wherein the martensite phase exists in a proportion such that an area ratio of the martensite phase in a structure cross-section is within a range from 1 to 10% of the matrix, and wherein a composition of the sintered valve guide comprises, by mass, 0.8 to 5.7% of Cu, 0.2 to 3.0% of Ni, 0.24 to 1.2% of P, and 0.5 to 1.5% of C, with a remainder comprising Fe and unavoidable impurities, and
wherein the martensite phase is of a size having an average area-equivalent circle diameter of 1 to 200 μm in a structure cross-section.
2. The sintered valve guide according to claim 1 , wherein the composition of the sintered valve guide comprises, by mass, 1.5 to 3.0% of Ni.
3. The sintered valve guide according to claim 1 , wherein the composition of the sintered valve guide comprises, by mass, 0.8 to 5.7% of Cu, 0.2 to 2.0% of Ni, 0.24 to 1.2% of P, 0.5 to 1.5% of C, and 0.01 to 1.5% of a machinability improver, with a remainder comprising Fe and unavoidable impurities.
4. The sintered valve guide according to claim 1 , wherein the matrix composed of a martensite phase dispersed in a mixed structure of ferrite and pearlite, and pores dispersed within the matrix, contains an Fe—P—C compound in the pearlite, and wherein the pearlite is partially micronized.
5. The sintered valve guide according to claim 3 , wherein the machinability improver comprises, by mass relative to the composition, at least one of 0.01 to 0.5% of boron nitride, 0.05 to 1.0% of a magnesium silicate mineral, and 0.1 to 1.5% of manganese sulfide.