Estudo sobre o pick-up de nitrogênio após a etapa de refino primário do aço

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

With the growing need of high quality steel there is a great demand for the development and production of steels with ever stringent chemical composition restrictions. For instance the presence of carbon and nitrogen in Interstitial Free steels for automobile industry. These restrictions are defined by the final application to which the product is destined. In the case of steels for application in drawing which require a minimum deformability the nitrogen content becomes a critical point. This study seeks to analyze the factors that determine the variation of the nitrogen content until the moment the liquid steel is released to the secondary refining station. This was accomplished by analyzing a database from ArcelorMittal Tubarão Steelmaking Shop. The data has been analyzed under a more practical point of view and in consonance with mathematical models, in such a way to identify the degree of influence of some operational parameters. Some conclusions could be reached: 1) The results showed that with the presence of slag, the pick-up of nitrogen is negligible. The average nitrogen pick-up between the end of blow and release of steel to the secondary refining station, 1 N D , was close to 5.5 ppm; the average nitrogen pickup between releasing the steel to secondary refining and the first sample taken in the secondary refining station, 2 N D , was 3.5 ppm. API steel grades are a special case of comparatively high pickup( 1 N D was 13.9 ppm and 2 N D was 7.6 ppm). API grades require heavy addition of alloy material (up to 5,000 kg) and aluminum (around 650kg) and bubbling with inert gas up to 10 minutes. These alloy additions and gas bubbling in the ladle are performed after tapping steel from the converter before releasing it to secondary refining stations. 2) A statistical evaluation of variables affecting nitrogen pickup was performed for both 1 N D and 2 N D . The most influential independent variables have been found to be mass of nitrogen in the Aluminum addition and liquid steel weight for 1 N D , and time of ladle bubbling for 2 N D . The value of adjusted R2 was 0.21 in regard to 1 N D regression and 0.09 for 2 N D regression; 3)_ The estimate of possible nitrogen pick-up through the "eye of the plume, using AM Tubarão data do not suggest a very significant value exception made for API grades ; argon rinsing alone do not explain all nitrogen pickup 4)_ The average nitrogen pick-up as determined through this work can be deemed small as compared to nitrogen pickup from secondary refining to continuous casting, which is around 15 or 20 ppm. Regardless the low value it must be taken in consideration when evaluating the feasibility of producing a given steel grade; 5)_ It was found that nitrogen pick-up is connected to the aluminum addition. This may be due to the release of interfacial sites previously occupied by oxygen or sulfur.

ASSUNTO(S)

aço - refinação nitrogênio gás engenharia de materiais e metalurgica

ACESSO AO ARTIGO

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