Abstract The effect of insert diameter and pouring temperature on the microstructure of gray iron are studied by inserting the copper wires with diameters of 0.4, 1, and 2 mm into polystyrene patterns, followed by pouring the gray iron melt at two temperatures of 1230 and 1370 °C. The graphite morphology in the reference sample (without copper insert) was type A flake graphite which changed to type B, D or E in the specimens containing copper insert. The aforementioned variations can be attributed to the degree of undercooling developed during solidification. Copper dissolved up to 0.9 wt.% in the matrix and copper particles exceeding the limits of solubility dispersed throughout the matrix or segregated at the bottom of the melt. The process utilized in the present research, can be regarded as a promising approach for in-mold alloying, production of bi-metals, and study the interfacial reactions between a given melt and a supposed solid insert.