The effects of alloying elements and microstructure on the impact toughness of powder metal steels

The impact toughness of powder metal steels is typically deteriorated when the strength is increased by adding specific alloying elements and modifying the microstructure. An earlier study by the authors demonstrated that the tensile strength and hardness of Ni-containing PM steels were much enhanced by the additions of Cr and Mo. To develop high-strength PM steels with high toughness, the effects of alloying elements and microstructure on the toughness were further investigated. sults showed that the toughness of binary Fe–C alloys was decreased by Mo and increased by Ni and Cr, though these three alloying elements improved the tensile strength. Mo also impaired the toughness of Fe–Ni–C alloys by the formation of low-toughness pearlite and bainite. However, the addition of Cr in the Fe–Ni–C alloys much improved the tensile strength without sacrificing toughness. This improvement was attributed to the formation of a large amount of tough Ni-rich martensite by adding Cr, which promoted the homogenization of Ni and C. As a result, a superior combination of tensile strength and impact toughness could be achieved, as demonstrated in the Fe–1.5Cr–0.2Mo–4Ni–0.5C steel compact.