Reinforced tantalum carbide particles were synthesized between tantalum wires and graphite in gray cast iron by heat treatment; the effects of different heat treatment times on the phase evolution, microstructure, and micro-hardness of the composites were investigated. The particles obtained were small and square-shaped, 1–2 µm in size, and evenly distributed through the cast iron. The maximum micro-hardness of the composite region was 1832 HV_0.1. After 20 min heat treatment, the micro-hardness decreased to approximately 1077 HV_0.1, between about four and five times that of the matrix. The resulting composites also presented higher wear resistance compared with unreinforced gray cast iron.