A plain carbon steel was poured at 1,560°C into Y-block CO
2 process mold in which 50
φ×50mm sand test pieces were set to make its end surface contact with molten steel. The 50
φ sand mold surfaces with zircon facing and without facing were observed by scanning electron microscope in order to obtain new information. In the green sand mold, the sticky features due to combination with bentonite were recognized in 1 to 6 hrs after molding, and the dry features in 24 hrs. When
α-starch was added, the sticky features were recognized even 24 hrs. In the CO
2 process mold more firm features were recognized. In the case of zircon facing, the mold surface became flat, hence the difference of the surface feature between green sand mold and CO
2 process mold descreased. The feature of steel casting surface was changed remarkably by zircon facing. In the case of zircon facing, the mold-metal interface became flat, and the mold-metal interface layer easily peeled off.
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