Abstract
Hardfacing (harden-surface-welding) metal of the hypereutectic Fe–Cr–C alloy with different La2O3 additives was developed. The microstructure of the hardfacing metal was observed by optical microscopy. The phase structure was determined by X-ray diffraction. The hardness and wear resistance of the hardfacing metal were measured by hardness tester and dry sand rubber wheel abrasive tester, respectively. The worn surface morphology was observed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometry. The solidification curve of the hardfacing metal and the relationship between the content of each phase and the temperature were calculated by thermodynamics software Thermo-Calc and Jmatpro, respectively. The results indicate that, with the increase of the La2O3 additives, the dimension of the primary M7C3 carbide in the hypereutectic Fe–Cr–C alloy hardfacing metal decreases gradually. When the La2O3 additive is 0.78wt.%, it reaches minimum, which is 11.37μm. The amount of M7C3 carbide (including the primary carbide and the eutectic carbide) decreases firstly then increases. The hardness of the hardfacing metal increases smally, while the wear resistance of it increases firstly then decreases and reaches the most excellent when the La2O3 additive is 0.78wt.%. The formation temperature of M7C3 carbide is higher than that of austenite in the hypereutectic Fe–Cr–C alloy hardfacing metal. Austenite precipitated in the liquid phase can improve the precipitation rate of M7C3 carbide in a certain extent. As the temperature of the molten pool drops from 870°C to 840°C, γ-Fe transforms into α-Fe completely, so a large number of C atoms precipitate, which promotes the growth of the M7C3 carbide in short period.
Published Version
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