Effect of Nb additive on wear resistance and tensile properties of the hypereutectic Fe-Cr-C hardfacing alloy

Abstract

The effects of Nb additive on wear resistance and tensile properties of the hypereutectic Fe-Cr-C hardfacing (harden-surface-welding) alloys were investigated. The microstructures and phase structures of the alloys with and without Nb additive were compared by means of optical microscopy (OM) and X-ray diffractometer (XRD). The wear behaviors were measured by reciprocating wear tests via CSM Tribometer. The tensile properties were measured by universal testing machine. In order to investigate the (Fe,Cr)7C3 carbides refinement by Nb additive, the formation thermodynamics of NbC and the misfit between NbC and (Fe,Cr)7C3 were calculated. The results show that the alloy with Nb additive contains NbC as well as (Fe,Cr)7C3 and γ-Fe. The size of the primary (Fe,Cr)7C3 carbides in the alloy with Nb additive is obviously smaller than that without Nb additive. The mass loss of the alloy with Nb additive is less than that without Nb additive. The worn surfaces also indicate that the amount of the cracks on the alloy surface with Nb additive is less than that without Nb additive. The tensile strength parallel to the rod-like primary (Fe,Cr)7C3 carbides is larger than that vertical to the primary (Fe,Cr)7C3 carbides. The tensile strength parallel to the primary (Fe,Cr)7C3 carbides of the alloy with Nb additive is larger than that without Nb additive, while the tensile strength vertical to the primary (Fe,Cr)7C3 carbides of the alloy is lower than that without Nb additive. The phase fraction vs. temperature curves of the alloy shows that the alloy with Nb additive preferentially forms NbC and then primary (Fe,Cr)7C3 carbides. The lattice misfit between NbC and (Fe,Cr)7C3 is 2.16%, which proves NbC can be as the heterogeneous nucleus to refine primary (Fe,Cr)7C3 carbides in the Fe-Cr-C hardfacing (harden-surface-welding) alloy.