Black spot defects appeared on the surface of the cold-rolled medium grade non-oriented silicon steel strip produced by a steel plant. SEM and GDS were used to analyze the microstructure and composition distribution of dark spots. By simulating the cold rolling and cooling process of steel strip, the formation mechanism of black spots was studied. The results of the study show that the black spots on the medium-grade non-oriented silicon steel strip are thin films with a thickness of 1 to 2 μm, the main component being oxides, and a small amount of organic matter and emulsion. The reason for the formation of black spots is: During the cold rolling process, the emulsion and iron powder adhere to the surface of the steel strip, and the moisture therein vaporizes at a rolling temperature higher than 100 ℃ to corrode the surface of the steel strip; the cooling process after coiling In the process, the metal atoms on the surface of the steel strip are ionized, causing electrochemical corrosion, and eventually black spots are formed. According to the causes of black spots, effective preventive measures are proposed: replace the emulsion, reduce the impurities mixed into the emulsion, improve the sweeping effect of the steel strip surface, and shorten the storage time of the steel strip.

   Cold rolled non-oriented silicon steel strip is a kind of high value-added soft magnetic functional material, which is widely used in motors, compressors, generators and other equipment. Whether it can produce high-performance cold-rolled non-oriented silicon steel strip can reflect the comprehensive strength of a steel enterprise in terms of equipment, technology, personnel, and control. In addition to the magnetic properties, the surface quality is increasingly being valued by users of non-oriented silicon steel strips. Ensuring the surface quality of non-oriented silicon steel strip has become a key task for silicon steel manufacturers. In the process of producing non-oriented silicon steel strips of medium grades in a steel plant, when uncoiling after cold rolling in a single-stand reversible rolling mill, it was found that there were many black strips on the surface of the steel strips that were difficult to clean, but the non-silicon steel strips produced at the same time did not This defect occurs. There are no reports in the literature about the occurrence of black spots after cold rolling of non-oriented silicon steel strips. Therefore, this article uses SEM-EDS (Scanning Electron Microscope & Energy Spectrometer) and GDS (Glow Discharge Atomic Emission Spectrometer) to analyze the microstructure and composition distribution of black spots; the formation mechanism of black spots is studied through simulation experiments; and here On the basis of this, measures to prevent the occurrence of black spots in cold-rolled grades of non-oriented silicon steel strips are proposed.

   

found in study:

(1) The black spot on the surface of the medium-grade non-oriented silicon steel strip is a 1 to 2 μm thick film with microcracks on the surface. The main composition is iron oxide, and contains a small amount of residual organic matter and emulsion.

(2) The main reasons for the black spots are: When the steel strip is cold rolled, the rolling temperature exceeds 100 ℃, and the water vaporizes and penetrates the oil film of the emulsion, so that the lipids in the oil are cracked into low-carbon chain acids, which are in contact with the surface of the steel strip. The iron powder reacts to corrode the surface of the steel strip, resulting in the formation of black spots or slight black spots; when cooled after coiling, the iron atoms on the surface of the steel strip are further ionized, resulting in an electrochemical corrosion reaction, which aggravates the black spots. .

(3) The measures to prevent black spots on the surface of medium-grade non-oriented silicon steel strips at the production site should be based on the rational use of emulsions, while reducing the impurities mixed into the emulsions, improving the cleaning quality on the surface of the steel strips, and shortening the cost of the steel strips. Storage time to ensure the use effect of the emulsion.

Source: "Shanghai Metal" Kong Wei et al