<p>The cooling rate is crucial for preparing cast iron using lost foam casting. Compared with traditional sand casting, the dry sand used in lost foam casting has poor heat transfer capacity, resulting in a relatively low cooling rate during solidification. In the present study, medium-chromium cast iron specimens produced by the lost foam casting process using different coating thicknesses were prepared, in which metal sand was used instead of traditional dry sand during the solidification process, in order to increase the solidification rate. The effects of EPS pattern thickness on phase composition, carbide morphology, and macroscopic properties of medium-chromium cast iron were systematically investigated. Results indicate that as the coating thickness increases, the austenite content in the casting increases, and the carbide morphology evolves from coarse chrysanthemum-like to plate-like and radial, and finally to fine chrysanthemum-like. Additionally, the hardness and wear resistance of the medium-chromium cast iron first increase and then decrease with increasing coating thickness, with the casting exhibiting the optimal performance at a coating thickness of 0.25 cm. When the coating is excessively thin, it fails to effectively adsorb the liquefied resin, leading to the blockage of coating pores and a prolonged molten metal filling time, which ultimately results in coarse grains and degraded material properties.</p>