The Control Measures Of Strip Defects On Cold Rolled Sheets Surface

Publish Time: 06/24 2021 Author: Site Editor Visit: 15989

Strip defect is a serious metallurgical defect on the surface of cold-rolled sheet. This type of defect extends along the rolling direction and is silver-white or black in the shape of thin lines, strips or bands, accounting for about 80% of the metallurgical defects on the entire surface. .

Cold-rolled lath defects are mainly three types: Al2O3 inclusions, mold flux inclusions and FeO. The analysis shows that the main reasons are: top slag oxidation, RH pure cycle time, protective slag performance, liquid level fluctuation, high-pressure water descaling equipment, and tapping temperature. To this end, the control measures are:

1. Modification of ladle slag

Different tapping slag modification modes are formulated according to the end-point oxygen content. After adding aluminum slag balls and metal etching white ash, the ladle is blown and stirred at a low flow rate to make the top slag uniform, and the oxidation of the top slag after the converter tapping is reduced. The refining needs to be modified twice. After aluminum is deoxidized, a certain amount of aluminum slag ball is added to the ladle slag surface to reduce the oxidation of the top slag again.

2. Chain use of slag detection

According to the amount of slag in the tundish, the sensitivity of slag detection was adjusted from 40% to 10%, and the slag detection chain was used to improve the pass rate of aluminum loss quality score.

3. Pure cycle time

By optimizing the RH washing bath and cold steel, reducing the secondary aluminum adjustment and optimizing the production organization, the pure cycle time is controlled at 6min or more, so that the Al2O3 type inclusions can be fully floated.

4. Ladle sedation time

The optimized ladle calming time is greater than 30 minutes, so that the clustered inclusions can fully float up and improve the purity of molten steel.

5. Optimize the performance of the protection law

Optimize the performance of the original mold powder, increase the viscosity of the mold powder, and match the viscosity with the pulling speed. The consumption of the mold powder does not change much, and the thickness of the liquid slag is increased to reduce the mold slag entrapment.

6. Fluctuation of the steel liquid level in the mold

By controlling the pulling speed, increasing the immersion depth of the tundish immersion nozzle, optimizing the nozzle shape, adjusting the argon gas flow, etc., the fluctuation of the steel liquid level in the mold is reduced, so that the liquid level fluctuation is within ±3 mm per pouring.

7. Lower the tapping temperature and transform the descaling water system

By strengthening the precise control of the tapping temperature and the temperature of the rolling process, the tapping temperature was reduced by an average of 50°C. In terms of equipment, the descaling water system was modified to reduce the FeO strip defects.

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