Mechanical properties of as-forged Ni-free Co–29Cr–6Mo alloys with ultrafine-grained microstructure

We have succeeded the fabrication of Ni-free Co–29Cr–6Mo alloys with ultrafine-grained (UFG) microstructures via conventional hot forging process with the reduction up to 83.4% (true strain of 1.8). Grain refinement to submicron order is an effective method for improvement of strength and athermal martensite ɛ phase formed during quenching seems to determine the ductility of this alloy system.

► Ultrafine-grained Co–29Cr–6Mo exhibits significantly high strength and low ductility.
► Factor for elongation of UFGed alloy is not related to plastic instability.
► The martensite ɛ phase inside the grains causes for premature fracture.