Abstract: In order to improve the cleanliness and reduce the cost of thin gauge high strength steel in CSP process, the change of the cleanliness of molten steel and the morphology, the size and the compositions of inclusions in WJX600 steel during refining were studied by industrial experiments. The industrial results showed that, the amount of calcium wire feeding had little influence on T.O of molten steel, the  T.O mass fraction of molten steel in tundish was less than 0.002 5 %, and nitrogen mass fraction was less than 0.004 %. The ratio of the inclusions with the size more than 10 μm increased with the amount of calcium wire feeding. The principles and the aim for inclusion modification by calcium were given by analysis. The judgement-changing rate of thin gauge high strength steel decreased to 0.48 % from 1.2 % by light calcium treatment and optimization of refining process.

Key words: thin gauge high strength steel, inclusions, calcium treatment, CSP process