It can be seen from the surface defects and improvement measures of the tinplate cold-rolled sheet that such defects on the tinplate cold-rolled sheet are composed of large-sized composite inclusions. The inclusions inside the inclusions have a bare steel matrix, indicating that the inclusions have a low melting point and undergo a large deformation during the rolling process, thus presenting a very thin layer on the cold rolled sheet. Roller Reamer,Oil Well PDC Reamer Bits,HDD Reamer With PDC Cutters CANGZHOU GREAT DRILL BITS CO., LTD , https://www.pdcbits.nl
Most of the inclusions detected have a high carbon content (10% to 25%) and are the product of the intermediate packaged slag. 4%。 The low-carbon content of the coating agent is 4. 4%. The covering agent has a low melting point and a small viscosity, and is easily mixed with the carbonized rice husk heat insulating agent. When the liquid level of the liquid is unstable or at the end of casting, the slag is formed into the molten steel, because the melting point of the leveling instrument is low, The steel is mainly liquid, has a strong ability to aggregate, and quickly reacts with other inclusions in the steel, and grows together to form a larger inclusion.
When the molten steel enters the crystallizer through the immersion nozzle, the size of such inclusions is large, and the melting point is low, and the floating ability is strong. Most of these inclusions can float up to the slag surface and are adsorbed by the mold flux. A small part of it is too late to float to the slag surface, and finally accumulates to the inner arc near the surface position. During the hot rolling and cold DIN cup rolling process, it is exposed to the surface of the cold rolled sheet due to large deformation, thus forming defects. Since such inclusions have a high floating ability, they are concentrated near the inner arc, so such defects occur only on one side of the cold-rolled sheet, and the other side does not find such defects.
The presence of K and Na elements was found in a part of the detected inclusions, indicating the presence of a mold flux component. This kind of inclusions contact with the protective slag and react with the flow field in the crystallizer, but due to the kinetic energy of the flow field, it is not adsorbed by the protective slag, and re-enters the molten steel with the flow field trace. As shown in Figure 7.
3 The improvement of the surface technology of tinplate cold-rolled sheet is the production of such defects in the barbest iron tester. The plant has adopted a series of process optimization measures, including the following aspects.
3. The tundish covering agent increases the alkalinity of the covering agent, and the alkalinity of the tundish covering agent is changed from 1.8 to 3. 7. The free carbon in the covering agent is strictly controlled to less than 1.5%, and the inner bag is optimized. The addition system of the covering agent.
3. 2 The operation of the middle package is controlled by the rhythm. At the end of the casting, when the molten steel level in the package is less than 300 mm, the casting is stopped. Through these measures, the phenomenon of tundish slag is basically eliminated.
3. 3 Crystallizer level The plant has a mold liquid level automatic control system. However, the pulling speed is not stable enough, and the immersion nozzle is not enough in place. In response to this situation, the plant was changed to constant speed operation and the nozzle was reinforced.
Centering operations management. Through the above process improvement measures, the quality of the tinplate sheet produced by the plant has been significantly improved, and there is no problem of surface inclusion defects.
4 Conclusion
(1) The strip-shaped defects on the cold-rolled sheet of tinplate mainly show the large-sized composite inclusions. The inclusions have a low melting point and produce large deformation during the rolling process, mainly distributed on one side of the cold-rolled sheet. Surface area.
(2) The inclusions on the surface of the tinplate cold-rolled sheet are the products of the medium-packed slag, which is mainly formed by the reaction with the mold flux, which is the main influencing factor for the formation of such defects in the tinplate cold-rolled sheet. Because of the lower melting point, it floats up to the vicinity of the inner arc during the casting process.
(3) After optimization and improvement of the tundish covering agent, the standard package operation, the constant speed operation of the tinplate and the operation management of the nozzle alignment, the problem of strip-shaped defects on the surface of the tinplate is effectively avoided.
This paper is mainly excerpted from Zhou Jinglong's "Study on Surface Defects of Tinplate Cold Rolled Sheet"
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