Carburisation with Lignite Coke

Depending on product percentage purity -which is mainly a function of carbon content and companion element contents -there is a relatively wide price band for this quality spectrum. In the past, many examples have shown that lignite coke is able to satisfy even stringent carburisation requirements at a much lower cost. The main reasons for the wide range of applications are to be found in the following product-specific properties and effects: .Lignite coke is distinguished specifically by its high reactivity and dissolving power it owes to its high porosity. The pore volume is approx. 50%, the specific surface area 300 m2/g.

The above-average product dissolution permits shorter treatment times and reliable adjustment of the carbon levels in the liquid steel. Even with very high additions of > 1 t per melt, the analytical accuracy is very high after a short time, obviating any additional and often very time-consuming post-alloying or post- carburising having a later effect.

Owing to the high lime content of some 40 %, the ash has a strong basic character. The basicity is comparable with that of typical steel mill slags. The coke ash melts homogeneously into the process slag. These properties of the ash form ideal prerequisites for ensuring that no inclusion-critical bonds are liberated in the steel melt. Even in the production of very alumina-, spinel or TiO2-sensitive steel qualities, such as rails, steel cord or anti-friction bearing steel, no adverse influences have been found so far. .Approx. 90 % of the sulphur content is bound in the coke ash and adsorbed by the slag together with the ash. As a result, the sulphur content relevant to the liquid steel is some 10% of the total sulphur. .The high dissolving velocity means a higher CO gas formation rate per unit of time with corresponding high nitrogen and hydrogen reduction effects. The driving power for rapid carbon conversion is the partial pressure difference in the CO bubbles; the nitrogen and hydrogen partial pressure is here near zero. In this connection, the small active sulphur portions reduce surface tension of the forming gas bubbles and, as a result, favours the N2 and H2 diffusion velocity into the CO bubble.

The volatile matter in the coke mainly consists of CO (2% wt.) and CO2 (1% wt.) and supports the degasification of the melt and circulation of the melt during steel tapping or secondary metallurgical steel treatment.

The Cfix yield is comparable with classic carburisation products, since the gas formation reactions described above take place in a relatively short time owing to the rapid dissolution of the product.

Summing up, it can be said that lignite coke from the Rhenish mining area is a carburising product that satisfies very high metallurgical requirements. In many cases, it provides a 100 % substitute for relatively expensive carburising products like graphites and needle cokes. In view of the raw material base that will be available far into the future, this will help ensure a calculable and low-cost product supply.

The volatile matter in the coke mainly consists of GO (2% wt.) and GO2 (1% wt.) and supports the degasification of the melt and circulation of the melt during steel tapping or secondary metallurgical steel treatment.

The Gfjx yield is comparable with classic carburisation products, since the gas formation reactions described above take place in a relatively short time owing to the rapid dissolution of the product.

Summing up, it can be said that lignite coke from the Rhenish mining area is a carburising product that satisfies very high metallurgical requirements. In many cases, it provides a 100 % substitute for relatively expensive carburising products like graphites and needle cokes. In view of the raw material base that will be available far into the future, this will help ensure a calculable and low-cost product supply.