Stainless steel powder intermixed with boron nitride powder for enhanced machinability of sintered powder metal parts

Abstract

An elemental powder or powder of compounds is disclosed consisting essentially of the primary metals chromium, nickel and molybdenum for blending with an atomized, prealloyed, stainless steel powder and followed by pressing the powder into a part for sintering includes an additive incorporated into the matrix of the stainless steel powder that enhances the machinability of the part and serves as a chip breaker. Among the candidate additives are hexagonal boron nitride, a powder with lubricating qualities, Monel Metal (Ni—Cu), cupro-nickel (Cu—Ni), and powders of electrical resistance alloys such as 80-20 alloy (80Ni—20Cr), 70-30 NiCr, Ni—Cr—Fe—Si alloys, and molybdenum disilicide (MoSi 2 ).

We claim:  
     
         1 . A blend consisting of pre-alloyed stainless steel powder consisting essentially of, by weight, up to 0.05% carbon, 22% to 26% chromium, 10% to 24% nickel, 2.7% to 5% molybdenum, 0.1% to 1% boron, up to 2.0% manganese, up to 2.0% silicon, balance iron and residuals, together with boron nitride particles added thereto essentially, by weight, from 0.25% of the pre-alloyed stainless steel powder upward.  
     
     
         2 . A sintered stainless steel having excellent resistance to corrosive attack by the chloride ion and improved machinability, said steel having an overall composition consisting essentially of, by weight, up to 0.05% carbon, 22% to 26% chromium, 10% to 24% nickel, 2.7% 5% molybdenum, 0.1% to 1.0% boron, up to 2.0% manganese, up to 2.0% silicon, up to 0.4% boron nitride, balance iron and residuals.