Characterization of the formation of nickel-rich areas in PM steels and their effect on mechanical properties

Admixed chemical elements may lead to the formation of heterogeneous microstruc-tures in sintered steels. This is due primarily to low bulk-diffusion coefficients at conventional sintering tem peratures. For powder met allurgy (PM) steels, admixed nickel is well known to produce such heterogeneous microstructures where the element is not distributed evenly upon sintering, resulting in the formation of nickel-rich areas (NRAsj. In contrast, the principal mechanisms of nickel diffusion in PM steels are often misunderstood. This work presents a new approach to measure the bulk-diffusion coefficients of nickel in PM steels in order to determine the sintering conditions required to maximize its homogeneity in a steel matrix. Also, the influence of the local concentration of nickel on sintered microstructures is discussed. The characterization approach presented here could be used to characterize the diffusion of other alloying elements in PM steels, either admixed as elemental powders or introduced via master alloys.Peer reviewed: YesNRC publication: Ye