Abstract
The origins of large nonmetallic inclusions in continuoulsy cast plain carbon steel billets have been investigated in relation to the mould scums. Three kinds of synthetic scums containing tracer elements of La, Ce or Ca individually are added into the liquid plain carbon steel in the continuous casting mould poured by means of an open nozzel, and inclusions in the billets are analysed in electron prove microanalyser. The results obtained are as follows.
1) In the inclusions larger than about 150μ in diameter, tracer elements are observed, but none in those smaller than about 100μ in diameter.
2) The compositions of large inclusions are similar to those of mould scums.
3) From these results it is concluded that most of large inclusions originate from mould scums.
