Steel with exceptionally low phosphorus content - made by treating molten steel with mixt. of calcium carbonate, sodium carbonate, ferric oxide, and fluorspar

摘要

Molten steel is refined in a vessel and the refining slag is removed. After refining, or shortly before the end of refining, when the unkilled steel contains 0.4% carbon, a carrier gas is used to inject a mixt. (I) deep enough into the melt in the refining vessel so thorough mixing of the steel with the slag formed by mixt. (I) occurs. The slag is then held back while the steel is tapped a ladle for a conventional final treatment. Mixt. (I) contains CaCO3 and Na2CO3 in ratio 1:1 and also up to 30 wt. % CaF2 and/or Fe2O3. The pref. mixt. (I) has a grain size 1 mm and consists f a stoichiometric mixt. forming the double carbonate CaNa2(CO3)2 and contg. 10% each of CaF2 and Fe2O3. Mixt. (I) pref. forms 1-3% of the melt. Apart from producing e.g. 0.0003% P in the steel, the process is undertaken in the refining vessel so a loss of temp. in the ladle is avoided.