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Calcium aluminate flux: controlling slag composition
Mastery of slag design in secondary metallurgy is crucial to performance in steelmaking. It guarantees the quality and cleanliness of the steel and the consistency of its performance. Thanks to it its special physical and chemical properties, calcium aluminate flux achieves rapid formation of slag and efficient steel refining in secondary metallurgy, in the continuous casting tundish and in foundries.


Imerys Aluminates invented the first calcium aluminate in 1908 and also developed the related fusion manufacturing process. It also pioneered the use of calcium aluminates as a metallurgical flux.

Many steelmakers regularly use these products today, even if only during processing in the ladle. Depending on the application protocol, their most significant advantages are improved steel quality, higher productivity, lower costs and better environmental protection.


The permanent quest for higher process efficiency and for improved steel quality has led steelmakers to develop new metallurgical tools and improve the slag formation process. Introducing a new reagent makes it possible for steelmakers to optimise the formation and composition of slag and obtain the desired improvement in performance.

The use of calcium aluminate flux improves traditional slag practices and even opens the way to superior performance:

Rapid slag formation

Thanks to its low melting point (< 1,325° - 1,375° C), calcium aluminate flux melts on contact with the steel, and can dissolve other reagents such as lime if the additions are proportioned correctly. It is thus possible to obtain a fluid and homogenous slag as soon as the ladle is filled at the end of tapping.

Improved desulphurisation kinetics
The rapid formation of slag enables the initiation of desulphurisation reactions as soon as the ladle is filled. Increased desulphurisation can:

  • achieve lower sulphur content and therefore higher steel quality
  • allow higher productivity thanks to shorter treatment time
  • reduce costs because of the possibility of using cheaper raw materials with higher sulphur content.

Steel cleanliness

The composition of calcium aluminate flux is close to that of the final slag composition, so it can start trapping non-metallic inclusions as soon as the ladle is filled. It is therefore possible to remove these impurities when they are formed and to reduce the need for subsequent processing.

Increased productivity
The consistency of calcium aluminate flux increases predictability and reproducibility of performance. Thus, the majority of the reagents are added during tapping, allowing the rapid formation of a fluid and homogeneous slag. In this way, the refining process starts earlier and is much faster and thus the overall processing time is reduced.

Cost reduction
Better alloy yields and globally optimised reagent additions, reduced corrosion of the refractory lining thanks to the elimination of fluoride flux and a shorter processing time all represent substantial cost savings which make the operation very profitable for steelmakers.



On the basis of its expertise and the detailed studies of slag processing carried out with metallurgists, Kerneos has developed specialised lines of metallurgical flux available throughout the world, both in bulk or packaged according to its customers' needs:

The LDSF® range
LDSF® has been used for over 25 years by many steelmakers for production of most types of steel, using all types of metallurgical production equipment.

LDSF® is a proven product in the metallurgy industry, with LDSF® RG, the standard flux, and LDSF® LT, a flux with low content in impurities, particularly in titanium.