Abstract: Based on piercing with a φ158 mm plug in a φ180 mm continuous rolling unit, 15Cr2Ni3MoW steel was selected as the plug material, and the smelting and casting processes were improved to decrease the casting flaws and increase the density of the plugs. After optimizing the heat treatment process, well-structured and organized oxide film overlays were found in the plugs. The metallurgical structures, flaws and inclusions in every production stage were observed and analyzed by metallographic microscopy and scanning electron microscopy. The service life testing of products in the φ180 mm continuous rolling unit shows a satisfied result.