Iron base sintered alloy with hard particle dispersion and method for producing same

A method for producing an iron base sintered alloy with dispersed hard particles comprising the steps of:

• preparing iron powder which contains molybdenum and chromium;
• mixing, with said iron powder material comprising carbonyl nickel powder, metallic molybdenum powder, graphite powder, and molybdenum iron to prepare raw material consisting by weight of 3 to 15% nickel (Ni), 3 to 15% molybdenum (Mo), 0.5 to 5% chromium (Cr), 0.5 to 2% carbon (C), the remainder iron (Fe) and unavoidable impurities;
• preparing 3 to 20% hard particles selected from the following three kinds of hard particles, each containing at least two selected from the following three kinds of hard particles:
• (1) 50 to 57% chromium, 18 to 22% molybdenum, 8 to 12% cobalt, 0.1 to 1.4% carbon, 0.8 to 1.3% silicon, and the remainder iron;
• (2) 27 to 33% chromium, 22 to 28% tungsten, 8 to 12% cobalt, 1.7 to 2.3% carbon, 1.0 to 2.0% silicon, and the remainder iron;
• and
• (3) 60 to 70% molybdenum, carbon less than 0.01%, and the remainder iron;
• adding the hard particles and zinc stearate to the raw material to make mixed powder;
• pressing the resultant mixed powder into a shape, heating for dewaxing, and sintering and cooling the shape;
• and
• further annealing the shape;
• whereby at least a part of said nickel, molybdenum and chromium is contained in solid solution of an iron base matrix;
• at least a part of said molybdenum and chromium is dispersed within the iron base matrix to form fine carbides or intermetallic compounds thereof;
• and said hard particles are uniformly dispersed within said iron base matrix.