In the previous article, we discussed slag entrapment prevention measures and highlighted the critical role of mold flux. Today, we delve into a decision-making issue that directly affects casting performance and slab quality: how to choose the right mold flux for your steel grade. Mold flux is the "lifeblood" of continuous casting, performing four major functions: lubricating the shell, controlling heat transfer, absorbing inclusions, and preventing steel oxidation. However, no single "universal" flux works for all steel grades. Choosing the wrong flux can lead to sticker breakouts, longitudinal cracks, deep oscillation marks, slag entrapment, and a host of other problems. How can you scientifically select the mold flux that matches your steel grade, casting speed, and equipment? Wuxi WeiDa Cored Wire Co.,Ltd provides customized mold flux selection services based on steel grade characteristics and process parameters.
The Core Logic of Mold Flux Selection: Matching, Not "Best"
Mold flux properties are determined by its chemical composition (basicity, Al₂O₃, Na₂O, F, Li₂O, etc.) and physical characteristics (viscosity, melting point, crystallization temperature, melting rate). The core principle of selection is: match the heat transfer and lubrication characteristics of the flux to the solidification shrinkage behavior of the steel grade. Steel grades with different carbon contents have vastly different solidification shrinkage characteristics, therefore their requirements for mold flux are also completely different.
Mold Flux Selection Guide by Steel Grade
First, low carbon steel (C<0.08%) . Low carbon steel does not undergo significant peritectic transformation during solidification; shell shrinkage is uniform. The primary requirement for mold flux is good lubrication to prevent sticker breakouts. Recommend using fluxes with low viscosity (0.8-1.2 poise at 1300°C) , low crystallization temperature, and low basicity (0.9-1.1) . Relatively higher heat transfer rates are permissible as low carbon steel is not sensitive to longitudinal cracks.
Second, peritectic steel (C=0.08%-0.15%) . Peritectic steel undergoes phase transformation shrinkage during solidification, making it most susceptible to longitudinal cracks and depressions. The requirements for mold flux are high lubricity + low heat transfer. Recommend using fluxes with medium viscosity (1.0-1.5 poise) , high crystallization temperature, and medium basicity (1.0-1.3) . The high crystallization temperature causes the flux to form a crystalline layer in the mold, which effectively "supports" the shell, improving heat transfer uniformity and reducing longitudinal cracks.
Third, medium carbon steel (C=0.15%-0.30%) . The degree of peritectic transformation is lighter for medium carbon steel. Requirements for mold flux fall between those for peritectic and low carbon steels. Recommend using fluxes with medium viscosity (1.0-1.4 poise) , medium crystallization temperature, and medium basicity (1.0-1.2) .
Fourth, high carbon steel (C>0.50%) . High carbon steel has low solidification shrinkage but high sensitivity to surface cracks and internal quality. Additionally, high carbon steel is often cast at lower speeds. Requirements for mold flux are good lubrication and good heat transfer uniformity. Recommend using fluxes with high viscosity (1.2-1.8 poise) , low crystallization temperature, and medium basicity (1.0-1.2) . High viscosity prevents excessive flux consumption, ensuring adequate lubrication at low casting speeds.
Fifth, special steel grades:
•Electrical steel: High silicon content reacts with SiO₂ in the flux, requiring low SiO₂, high basicity flux.
•Titanium-containing stainless steels (321, 409, etc.) : Titanium reacts with SiO₂ and moisture in the flux, requiring ultra-low SiO₂, low moisture specialized flux.
•High-aluminum steels (TRIP, TWIP, etc.) : High aluminum content reacts violently with SiO₂ in the flux, requiring SiO₂-free, CaO-Al₂O₃ system flux.
Effect of Casting Speed on Mold Flux Selection
Casting speed is another critical parameter. Higher casting speeds result in faster flux consumption, requiring selection of lower viscosity, faster melting rate fluxes to ensure sufficient liquid slag supply per unit time. Conversely, lower casting speeds require higher viscosity fluxes to prevent excessively thin liquid slag layers due to rapid consumption.
Our Service: Customized Mold Flux and On-Site Technical Support
Wuxi WeiDa not only provides standardized mold flux products but, more importantly, offers customized development services. Based on your specific steel grade, slab cross-section, casting speed range, mold parameters, etc., we can tailor the best-matched flux for you – from formulation design and property testing to on-site trials. Additionally, our technical team provides on-site tracking and parameter optimization services to ensure the flux performs as expected in actual production.
If you are confused about mold flux selection or wish to improve slab quality through flux optimization, please visit https://www.weidamaterials.com/ to contact our mold flux technology experts.