Abstract
A new refining method has been developed for producing ultra low nitrogen steels. Powdered oxidizer was blown onto the molten steel using a special top lance with the argon gas under reduced pressure. As the results, it was found that the nitrogen removal index increased twice as much as that in the oxygen gas blowing and the final nitrogen content could be lowered below 10 ppm easily. The reasons why the satisfactory nitrogen removal was obtaind by using this new method are considered as summarised below.
(1) The gas-metal interfacial area was increased to twice or five times as large as that the oxygen gas blowing due to the formation of large number of fine CO bubbles during the powdered oxidizer blowing. (2) The oxygen content was maintained at a low level, because the oxidizer efficiency of decarburization reaction was quite high due to the existence of oxidizer particles as nuclei of CO bubble-formation which were penetrated deeply in the molten steel.
