Fe–0.4 wt.%C–6.5 wt.%Cr hardfacing coating: Microstructures and wear resistance with La₂O₃ additive

Highlights: • Fe–0.4 wt.%C–6.5 wt.%Cr hardfacing coatings with different La₂O₃ additives were developed. • The grain size of the hardfacing coating decreases with the increase of the La₂O₃ additives. • The unidirectional wear resistance of the hardfacing coating is increased with the increase of the La₂O₃ additives. • The friction coefficient is decreased and the reciprocating wear resistance is increased with the increase of the La₂O₃ additives. - Abstract: Flux-cored wires with different La₂O₃ additives were developed. The microstructures of the hardfacing coatings were observed by optical microscopy (OM) and field emission scanning electron microscope (FESEM). The phase structures were determined by X-ray diffraction (XRD). The hardness, wear resistance and friction coefficient of the hardfacing coatings were measured by Rockwell hardness tester, unilateral abrasive belt wear testing machine and CETR reciprocating wear testing machine, respectively. At last, the worn morphologies of the hardfacing coatings were observed by FESEM. The results indicate that, the microstructures of the hardfacing coatings consist of needle-like martensite, high alloy matensite and retained austenite. With the increase of La₂O₃ additive, the high alloy matensite dissolves in the matrix gradually and the amount of retained austenite is not changed basically after it is increased firstly. When La₂O₃ addition is 0.70 wt.%, the grain size of the hardfacing coating is the smallest, which is 18 μm and the average hardness is the highest. Unidirectional abrasive belt wear test shows that the high alloy martensite can be as wear-resistance phase during the wear process of the hardfacing coatings. When the La₂O₃ addition is 0.35 wt.%, the unidirectional wear resistance of the hardfacing coating is the highest. Reciprocating wear test shows that with the increase of the La₂O₃ additives, the friction coefficient is decreased and the reciprocating wear resistance is increased. When La₂O₃ addition is 0.70 wt.% the reciprocating wear resistance is the highest