The purity of the cast billet is primarily determined by the treatment process applied before the molten steel enters the mould. How can we minimize the inclusion content in billets? Currently, several methods are used, including appropriate refining processes, tundish metallurgy, and protective pouring operations. The quantity, morphology, and distribution of non-metallic inclusions significantly affect billet purity. Therefore, it is essential to adopt effective measures to reduce steel inclusions to required levels.
Tapping Without Slag
Preventing slag from entering the ladle is critical. For example, converters can use slag balls to block slag flow, while electric arc furnaces should adopt eccentric bottom tapping to minimize slag carryover.
Ladle Refining
Selecting proper ladle refining techniques ensures uniform temperature distribution, fine-tunes the chemical composition (based on steel grade), reduces oxygen content, and helps remove gas and non-metallic inclusions.
Oxidation-Free Pouring
After ladle treatment, the total oxygen content of the molten steel is significantly reduced. However, if the pouring process from ladle to tundish is unprotected or poorly protected, reoxidation may occur, increasing the total oxygen in the tundish and compromising the effect of refining.
Tundish Design
Using a tundish with a large capacity and well-designed structure (e.g., V-shaped retaining walls, turbulence suppressors, vortex dampers) can help prevent slag entrapment and promote uniform mixing of the molten steel.
Submerged Nozzle
The material, shape, and insertion depth of the submerged nozzle should facilitate the floatation and separation of inclusions, further enhancing the cleanliness of the steel.
