Defects analysis for bright spots on surface of electro-zinc coated sheet

• The bright dots defects come from the mixed-grains.
• Coarse grains have approximate orientations, and it strengthens the direct reflection.
• Bright dots inherited and magnified the surface defects of primary steel sheet.
• The mixed-grains defects can be avoided by some methods.

The painting effect of products would be affected if the bright spots happen on the surface of electro-zinc coated sheet. The defects of bright spots are researched by macroscopical observation, scanning electronic microscope, X-ray energy spectrometer, metallography microscope and the electron back-scatter diffraction (EBSD). The result shows that the defects of bright spots are inherited by mixed-grains on the surface of primary steel sheet. It could be solved by controlling the annealing temperature of cold-rolled steel sheets, increasing the rolling reduction or strain rate when the sheets are rolled and uniform heat treatment to the original austenite grains in the continuous metal casting blank.Electro-zinc coated steel sheets are widely used in automobile and apparatus industry. The appearance is more instruct besides its mechanical and corrosion resistant property. Some tiny defects would affect the painting effect of products. Once the bright spot defects were found on the surface of electro-zinc coated steel sheet in some steel works and the appearance of electro-zinc coated steel sheets become bad. In order to finding how the bright spots happened and how to eliminate the defects in the end, rounded analysis is made by some inspections.