Effect of networked Cu-rich ferrite phase on proof stress and ultimate tensile strength of sintered bodies of Fe–Cu hybrid-alloyed steel powder with graphite

To improve the yield strength of powder metallurgy steel, this work investigated the effect of a Cu-rich networked phase. Mixtures of 0.7% graphite and Fe–3% Cu hybrid-alloyed steel powders, composed of pre-alloyed Fe–3 x % Cu particles with diffusion-bonded 3(1 − x) % Cu (0 ≤ x ≤ 1), were processed by high-density compaction and conventional sintering. The maximum values of 0.2% proof stress (YS) and ultimate tensile strength (UTS) were obtained at x = 0.68, where high-density compact with well-networked Cu-rich ferrite phase was developed without Cu growth. Moreover, nanosized ϵ-Cu precipitates were observed in the Cu-rich ferrite. These high YS and UTS were achieved not only by decreases in porosity but also by precipitation strengthening caused by the nanosized ϵ-Cu in the Cu-rich ferrite network.