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Effects of Carburising Agents on the H S N in an Oxygen Converter Steel Plant

Against the background of the impact carburising agent constituents have on the elements hydrogen, sulphur and nitrogen in the steel, comparative tests using 2 different graphite products and lignite coke were performed in a German oxygen steel mill. The products were used in the production of "high carbon" steel qualities with special carbursing agent requirements of 6.5 kg/t steel during converter tapping. The dissolving behaviour of all products was outstandingly good despite this relatively high dose. The attached overview summarises the results described below.

C yield
The yield rates of all tested products were well over 90%, and no post-carburising was detected. Lignite coke reached the highest C yield of 99%.

Hydrogen
Despite a significantly higher initial value of lignite coke, the hydrogen content in the steel was between the results of the other two graphite products.

Sulphur
The low sulphur content of the graphite products had practically no impact on the steel. Lignite coke led to an increase of +/- 0.001% wt. (10 ppm). This value is well under the theoretical sulphur addition as shown in the product analysis. This is mainly due to the fact that a large portion of the sulphur content (90-95%) is already bound in the basic, i.e. lime- containing coke ash.

Nitrogen
Lignite coke had the least influence on the nitrogen content of the steel, although the product analysis showed a much higher initial value than that of the reference products. This surprising result confirms the experience made by numerous users who found that the nitrogen quantity added by lignite coke is minimal compared with alternative carburising agents.

Conclusion
Lignite coke is suitable to replace high-quality carburising agents. In addition to the cost advantage, process engineering and metallurgical benefits with regard to dissolution velocity, a quick consistent carbon result and nitrogen addition may arise even in comparison with such analytically pure products.

Numerical results

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