The effect of niobium element on the as-cast microstructure of the hypereutectic high chromium cast irons containing 4.0 wt.% C and 20.0 wt.% Cr was studied by means of the optical microscopy, the scanning electron microscopy, the X-ray diffraction, the energy dispersive X-ray spectrometry, the electron probe microanalyzer and the Leica image analyzer. With the addition of Nb, NbC carbides are formed in the hypereutectic high chromium cast irons, the carbides are refined and the shape of the primary M_7C_3 carbides becomes isotropic. The addition of niobium reduces the carbon content of the liquid due to the formation of the first precipitated NbC, thus reduces the volume fraction and size of the primary M_7C_3 carbides.
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