The Air Reoxidation and the Formation of Large Inclusions in Continuous Casting Process

Abstract

A study was made of non-metallic inclusions in medium or high carbon steel billets which were cast by the six strands S-type continuous casting machine of Kokura Works, Sumitomo Metal Ind., Ltd. The way of avoiding large silicate inclusions was also investigated.
As the result, the reoxidation by air during casting was found to be detrimental in producing high quality steel grades by continuous casting. Many kinds of large silicates even if they are chemically unstable can exist in large quantity when the tundish stream was not protected from air.
In order to avoid those silicates, it was shown that the oxygen content of the atmosphere around the stream must be maintained under 0.8%. The mechanism of the silicate formation and its growth are discussed on the basis of the test results.