An investigation was done on the entrapped scums and pinholes in continuously-cast plain carbon steel billets of 80 to 160 square and 260 by 370mm section. The results obtained are summarized as follows:
1) The number of entrapped scums in the billets cast with open nozzles and oil was increased with decreasing manganese-to-silicon ratio and carbon content in the steels, excess addition of aluminum wire in a mold, addition of titanium to a low manganese steel, air oxidation of teeming stream in a mold, and increasing billet size.
2) Utilizing submerged nozzles and fluxing powders remarkably removed such scums.
3) These observations are discussed in terms of the melting point, fluidity, interfacial tension, and the amount of scums formed.
4) The number of pinholes in the billets cast with open nozzles and oil was decreased with decreasing carbon content of the steels, by using strong deoxidizers such as aluminum, calcium-silicide, or titanium, protecting air oxidation, drying ferroalloys, and with decreasing billet size. The use of water-free fluxing powders perfectly prevented the formation of pinholes.