Fe–24wt.%Cr–4.1wt.%C hardfacing alloy: Microstructure and carbide refinement mechanisms with ceria additive

Abstract

The microstructure and carbide refinement mechanisms of Fe–24 wt.%Cr–4.1 wt.%C hardfacing alloys with 0 wt.%, 0.5 wt.%, 1.0 wt.%, 2 wt.%, and 4 wt.% ceria additives have been systematically investigated in this work. Optical microscopy, field emission scanning electron microscopy with energy dispersive spectrometer, and X-ray diffraction were collectively used to study the microstructure, the phase components, and the chemical formation of inclusion formed in the welding process. Wear-resistance of the alloys was comparatively studied using an abrasive wear testing machine. The structure analysis results show that the Fe–Cr–C hardfacing alloy mainly consists of martensite, retained austenite, MC carbide and M7C3 carbide. With increasing ceria additive contents, the average size of the primary M7C3 carbide decreases and reaches a most refined state in the alloy with 2 wt.% ceria additives. Comparative wear tests data shows that the wear resistance of the hardfacing alloys with ceria additives is better than that without ceria additive. In a good agreement with the carbide refinement results, the wear resistance of the alloy reaches an optimum level in the sample with 2 wt.% ceria additive. The main RE inclusion type identified with in-situ XRD analysis is RE inclusion Ce2O2S. Thermodynamics calculation confirms that this type of RE inclusion could precipitate prior to M7C3 carbides, and act as a heterogeneous nucleus for M7C3 in the welding process, which effectively provides a mechanism for significant refinement of the M7C3 carbide and improves its wear resistance.