Abstract: This invention relates to valve seats that are made of a sintered Fe-base alloy that has high wear resistance, that is less hostile to valves and that hence is suitable for use with internal combustion engines such as diesel engines and gasoline engines, particularly those having high power outputs, the sintered Fe base alloy comprising a sintered Fe base alloy substrate having such a structure that hard particles A that contain 25-45% Cr, 20-30% W, 20-30% Co, 1-3% C, 0.2-2% Si and 0.2-2% Nb, with the balance being Fe and incidental impurities, and hard particles B that contain 55-65% Co, 25-32% Cr, 7-10% Mo and 1.5-3.5% Si, with the balance being Fe and incidental impurities, are dispersed in a total amount of 10-25% in an Fe base alloy matrix that contains 1-3% Cr, 0.5-3% Mo, 0.5-3% Ni, 2-8% Co, 0.6-1.5% C and 0.2-1% Nb, with the balance being Fe and incidental impurities, and which has a structure that is mainly composed of a pearlitic and a bainitic phase, all the percents being on a weight basis.

Abstract: An Fe-base sintered alloy for valve seats for use in internal combustion engines and a method of manufacturing the same are provided. The alloy consists essentially of 0.6 to 1.3% C, 1 to 5% Cr, 4 to 15% Mo, 0.5 to 2% Ni, 2 to 8% Co, 0.2 to 2% Nb, 0.2 to 2% at least one lubricating component selected from the group consisting of a CaF.sub.2 and BaF.sub.2 and the balance of Fe and inevitable impurities. Starting powders are blended into the same composition as above, and mixed into a mixed powder. The mixed powder is pressed into a green compact. Then, the green compact is presintered, hot forged, sintered, and, if required, further heat treated, in sequence to be formed into an Fe-base sintered alloy having a structure wherein particles of the at least one lubricating component and hard particles of other components are dispersed in a matrix formed principally of a pearlite phase. The resulting alloy possesses a density of at least 7.3 g/cm.sup.

Abstract: A main raw material powder comprising cobalt oxide powder, chromium oxide powder and carbon powder is added with at least one metal oxide powder selected from the group consisting of manganese oxide powder, vanadium oxide powder, titanium oxide powder, tantalum oxide powder, niobium oxide powder, boron oxide powder, hafnium oxide powder, tungsten oxide powder, molybdenum oxide powder, iron oxide powder, nickel oxide powder and copper oxide powder; these powders are then mixed and pulverized to prepare a mixed powder; said mixed powder is then reduced by heating under vacuum or in a reducing atmosphere to obtain a reduced sponge-like mass; said sponge-like mass is finely pulverized, thereby manufacturing a cobalt-base reduced powder.A cobalt-base sintered alloy, produced by using said cobalt-base reduced powder thus manufactured as the material powder, has a relatively wide range of diffusion sintering temperatures applicable at the time of sintering thereof and has furthermore a high sintered density.

Abstract: A nickel-base sintered alloy which comprises: being manufactured from a reduced powder by the conventional powder metallurgy process with said reduced powder as a material powder, said reduced powder being prepared by simultaneously reducing a mixed powder consisting of powders of oxides of elements constituting said sintered alloy with a carbon powder added and mixed therein, and said reduced powder consisting of powders of said constituent elements and powders of carbides thereof; and consisting essentially of, in weight percentage:______________________________________ chromium from 10.0 to 35.0 % tungsten from 0.5 to 15.0 % cobalt from 0.2 to 12.0 % molybdenum from 0.1 to 20.0 % iron from 0.1 to 20.0 % titanium from 0.05 to 2.00 % silicon from 0.05 to 1.50 % manganese from 0.05 to 1.00 % carbon from 0.1 to 3.5 % ______________________________________And the balance nickel and incidental impurities.The above-mentioned nickel-base sintered alloy, also containing, in weight percentage, from 0.05 to 1.

Abstract: A cobalt-base sintered alloy which comprises: being manufactured from a reduced powder by the conventional powder metallurgy process with said reduced powder as a material powder, said reduced powder being prepared by simultaneously reducing a mixed powder consisting of powders of oxides of elements constituting said sintered alloy with a carbon powder added and mixed therein, and said reduced powder consisting of powders of said constituent elements and powders of carbides thereof; and consisting essentially of, in weight percentage:Chromium from 15.0 to 35.0%Tungsten from 3.0 to 19.0%Nickel from 0.2 to 12.0%Molybdenum from 0.1 to 15.0%Iron from 0.05 to 5.00%Titanium from 0.05 to 2.00%Silicon from 0.05 to 1.50%Manganese from 0.05 to 1.00%Carbon from 0.2 to 3.5%AndThe balance cobalt and incidental impurities.The above-mentioned cobalt-base sintered alloy, also containing, in weight percentage, from 0.05 to 1.00% boron.