Chromium carbide overlays (CCO) with various aluminum contents are fabricated by button melting method and characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and nano scratch tests. During solidification, aluminum oxide may have formed first, followed by the nucleation of primary carbides, and subsequently the formation of eutectics. The existence of aluminum oxide in the melt seems to have provided more heterogeneous nucleation sites for the primary M7C3 carbides. On the other hand, the aluminum content raises the eutectic reaction temperatures so that the primary carbide growth ends at higher temperatures with an increase of aluminum concentration. As a result of the combined effect of nucleation and growth, the primary carbide size is refined with the increased aluminum concentration. The CCO’s resistance to scratch wear as a function of aluminum content and carbide sizes is discussed.