Patent ID: 6126894
Filing Date: 2000-10-03
Classification: B22F,C22C

Abstract:
Method of producing high density sintered articles from iron-silicon alloys comprising:(a) blending compressible iron or low-carbon steel powder, any one of silicon alloyed iron, silicon powder, or a combination of silicon alloyed iron and silicon powder, and a lubricant, to form a blended mixture,(b) cold pressing said blended mixture at a pressure less than 50 tsi to form a porous metal article with a density up to 88% of theoretical value, said article comprising hard powder consisting of silicon and/or silicon alloyed particles uniformly distributed among ductile iron or low carbon steel powder,(c) low temperature stress relieving heat treatment of said formed article at a temperature range of 360-800.degree. C. followed by cooling at a cooling rate of less than 120.degree. C./min to relieve compression stresses in said iron or low carbon steel particles inside said formed article, while avoiding substantial diffusion of silicon from said hard powder into said ductile iron or low carbon steel powder,(d) impregnating or lubricating said formed article to a degree sufficient to provide hydrostatic pressure and radial plastic flow of the porous metal in a subsequent pressing operation,(e) densifying said formed and stress relieved article by cold pressing to a density not less than 91% of theoretical value using the same pressure as in step (b), and finally(f) sintering the said formed article to obtain a density greater than 96% of theoretical value at an elevated temperature of from about 1250.degree. C. to about 1420.degree. C.