In the previous article, we discussed how to eliminate centerline porosity in continuous casting slabs. Today, we focus on another key quality indicator for continuous casting slabs: surface quality. Defects such as surface cracks, deep oscillation marks, and slag entrapment are "amplified" during subsequent rolling, leading to surface defects on hot-rolled coils, blisters on cold-rolled sheets, and cracks on bars and wire rods. For high-end products such as automotive panels, home appliance steels, and tinplate substrate, surface quality is the key to entering the high-end market. How can you systematically improve the surface quality of continuous casting slabs? Wuxi WeiDa Cored Wire Co.,Ltd provides a comprehensive solution ranging from mold metallurgy and mold flux optimization to steel cleanliness improvement.
Root Causes of Surface Defects
First, non-uniform heat transfer in the mold leads to uneven shell thickness and cracks. Second, improper mold flux properties cause poor lubrication or heat transfer. Third, poor steel cleanliness leads to subsurface slag entrapment. Fourth, improper oscillation parameters result in excessively deep oscillation marks. Fifth, excessive level fluctuation increases slag entrapment risk. Traditional measures such as reducing casting speed or increasing conditioning, while effective, sacrifice efficiency or increase costs, requiring a systematic solution.
Our Solution: Full-Process Control
First, optimize mold flux selection. For low carbon steel, select low viscosity (0.8-1.2 poise) flux to ensure lubrication. For peritectic steel, select high crystallization temperature, medium viscosity (1.0-1.5 poise) flux to reduce longitudinal cracks. For medium and high carbon steel, select medium viscosity, medium crystallization temperature flux to balance lubrication and heat transfer.
Second, optimize oscillation parameters. Use high-frequency, small-amplitude (frequency 180-300 cpm, amplitude 3-6mm), with negative strip time controlled at 0.08-0.12 seconds. For high-quality steel grades, recommend non-sinusoidal oscillation to further reduce oscillation mark depth.
Third, stabilize level control. Use electromagnetic level control systems to keep fluctuations within ±3mm, maintain stable casting speed, and optimize SEN design (port angle 15-25° downward, immersion depth 120-160mm).
Fourth, improve steel cleanliness. Through precision calcium treatment, modify Al₂O₃ into low-melting-point globular inclusions for flotation; use full protective casting to prevent secondary oxidation; optimize flow field with tundish weirs and dams.
Fifth, optimize mold cooling. Control temperature difference between inlet and outlet at 6-8°C, use soft water cooling, and for peritectic steel, appropriately reduce cooling intensity.
Sixth, use microalloying to improve high-temperature ductility. Titanium microalloying (0.01%-0.03%) refines grains; boron microalloying (0.001%-0.003%) improves grain boundary strength; rare earth treatment (20-50 grams per ton) modifies inclusions.
Quantifiable Benefits
After adopting the solution, customers typically achieve: surface crack rate reduced by 50-70% , oscillation mark depth reduced by 30-50% , slag entrapment defects reduced by over 60% , and conditioning volume reduced by 40-60% .
From "Passive Conditioning" to "Active Control"
Surface quality is not "conditioned" into existence, but "cast" into existence. Through the synergy of flux selection, oscillation, level control, cleanliness, and microalloying, you can improve slab surface quality at the source.
If you are troubled by surface cracks, slag entrapment, or excessively deep oscillation marks on slabs, please visit https://www.weidamaterials.com/ to obtain the complete solution.