Effects of Graphite Additions on Microstructures and Wear Resistance of Fe-Cr-C-Nb Hardfacing Alloys

Hardfacing alloys with different carbon contents by changing graphite additions in flux-cored wires were prepared on a surface of steel C45E4 (ISO 683) using open-arc overlaying. Testing was conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), a Rockwell hardness tester and an abrasion tester to study the effect of variation of graphite additions on the microstructures, hardness and abrasive resistance of the hardfacing alloys. The results show that the microstructures of the hardfacing alloys consisted of ferrite, martensite, retained austenite, independent austenite and NbC particles. Firstly, as graphite additions increased, the carbon contents gradually increased and the microstructures of the hardfacing alloys changed from ferrite plus NbC particles to martensite with retained austenite and larger NbC particles, which was accompanied by hardness increasing and better abrasive resistance. And then the hardfacing layer alloy best performance was obtained as graphite addition was 60 g. The highest hardness was 61.8 HRC and the wear resistance was nearly four times as high as that of the base metal. But excessive graphite additions resulted in some independent austenite present in the microstructures of the hardfacing alloys together with martensite plus retained austenite and NbC particles, which deteriorated the performance of the hardfacing alloys