Properties of a powder metallurgy low-alloy steel with varying fractions of large iron particles

Interiors of coarse iron particles in blends used in powder metallurgy may not be adequately alloyed during sintering. Relatively low concentrations of alloying elements reduce the hardenability of these regions, which may not transform to martensite during quenching. Since an actual microstructure (martensite, pores and pearlite) may differ from the desired microstructure (martensite and voids), it is reasonable to speculate that large and relatively soft pearlitic inclusions may worsen mechanical properties. This conjecture was tested, and it was experimentally found that unless the fraction of coarse particles exceeded a certain threshold, the properties of a medium-density powder metallurgy steel did not vitiate significantly. It also was observed that when the fraction of large particles dropped below a certain limit, apparent density, compressibility and flowability degraded to an extent rendering the corresponding mixtures unusable.A contradiction between a visual perception and a verdict of a statistical analysis is commented upon.