Fracture toughness of some high density PM steels

Tensile strengths, impact energies, and fracture toughness data are present ed for pure Fe-0.5C, Astaloy A with 0.2 and 0.6%C, and for Distaloy AB-0.6% C at relative densities of about 0.9, achieved by conventional pressing and sintering, and at close to 1.0, achieved by powder forging. At low relativ e density, properties are controlled by sizes of sinter necks; it is postul ated that toughness scales as (x/a)(4), x/a being the ratio of neck diamete r to particle diameter. At high relative density, microvoid coalescence and good toughness is observed for low strength microstructures whereas cleava ge and poor toughness is a concomitant of high strength.