Following our discussion on refining slag optimization for ultra-low sulfur steel, we turn to one of the most challenging steel grades in continuous casting: peritectic steel. During the solidification of peritectic steel (carbon content between 0.08% and 0.15%), a δ→γ peritectic phase transformation occurs, accompanied by approximately 0.38% volume shrinkage. This drastic volume change leads to uneven initial shell shrinkage, making the slab surface highly susceptible to longitudinal cracks, depressions, and even breakouts. For products like automotive high-strength steel, line pipe steel, and electrical steel, surface quality control of peritectic steel is key to ensuring smooth production and high product yield. How can you fundamentally prevent surface cracks during peritectic steel continuous casting to achieve stable, efficient production? Wuxi WeiDa Cored Wire Co.,Ltd provides comprehensive solutions based on mold flux optimization and mold metallurgy control.
The Peritectic Steel Challenge: Phase Transformation Shrinkage and Stress Concentration
During the solidification of peritectic steel, the transformation from δ-ferrite to γ-austenite results in a linear shrinkage of approximately 0.38%, far exceeding that of other carbon ranges. This drastic shrinkage causes the initial shell to lose contact with the mold copper plate, forming an air gap. The air gap leads to uneven heat transfer, locally thinning the shell. Under the combined action of thermal and mechanical stresses, these weak spots develop longitudinal cracks. Traditional solutions – such as reducing casting speed or lowering cooling intensity – while effective, sacrifice production efficiency. The key question is: how can you improve heat transfer uniformity and shell growth uniformity within the mold without sacrificing productivity?
Our Solution: High-Toughness Mold Flux and Mold Metallurgy Optimization
Wuxi WeiDa provides specially designed high-toughness mold fluxes for casting peritectic steel. Unlike ordinary mold fluxes, peritectic steel fluxes need to possess the following characteristics:
1.Relatively high crystallization temperature: The flux forms a dense crystalline layer on the inner wall of the mold. This crystalline layer can "support" the liquid slag film, allowing it to more uniformly fill the air gap between the shell and the copper plate, thereby improving heat transfer uniformity.
2.Appropriate viscosity and basicity: The basicity of peritectic steel mold flux is typically controlled between 1.0 and 1.3, and the viscosity at 1300°C between 0.8 and 1.2 poise, to ensure effective lubrication while providing sufficient heat transfer resistance.
3.Controlled crystallization rate: The crystallization rate of the flux needs to match the casting speed – too fast leads to poor lubrication, too slow fails to provide effective support.
Key Parameters for Mold Metallurgy
Beyond the mold flux itself, the metallurgical conditions within the mold are equally critical. Wuxi WeiDa's technical team can assist you in optimizing the following parameters:
•Mold level control: Keep level fluctuations within ±3mm to avoid slag entrapment and abnormal shell growth at the meniscus.
•Mold taper: For peritectic steel characteristics, parabolic taper or multi-stage taper is recommended to better match the shell's shrinkage curve.
•Cooling water intensity: Appropriately reduce the intensity and flow rate of mold cooling water to slow the cooling rate of the initial shell and reduce phase transformation stress.
•High-frequency, small-amplitude oscillation: Adopt a high-frequency, small-amplitude mold oscillation mode to improve oscillation mark quality and reduce surface defects.
Microalloying Assistance: Reducing Crack Susceptibility Through Composition Design
Beyond casting parameters, the steel composition itself significantly influences crack susceptibility. Wuxi WeiDa's cored wire technology can assist in reducing peritectic cracks through composition design:
•Titanium microalloying: By feeding ferro titanium cored wire, fine TiN and TiC particles are formed, refining the solidification structure, reducing segregation, and improving the high-temperature ductility of the shell.
•Rare earth treatment: As discussed previously, rare earths can modify sulfide and oxide inclusions, improving the steel's high-temperature ductility, thereby reducing crack risk.
•Boron microalloying: Appropriate amounts of boron can improve grain boundary strength, enhancing crack resistance.
Systematic Solution: Saying Goodbye to Peritectic Cracks
Surface crack control for peritectic steel cannot be solved by a single measure. Wuxi WeiDa's strength lies in providing a systematic solution: from the selection and supply of specialized mold fluxes, to optimization recommendations for casting parameters, to compositional fine-tuning via cored wire. Our technical team possesses extensive experience in peritectic steel production and can develop a customized peritectic steel continuous casting process package tailored to your specific steel grades and equipment conditions.
If you are producing peritectic steel and struggling with surface cracks and depressions, wishing to achieve defect-free continuous casting, please visit https://www.weidamaterials.com/ to engage in an in-depth discussion with our continuous casting experts.