Cause analysis and control of dark spot defects in hot-dip galvanized Si-Cr high strength duplex steel
By means of scanning electron microscope(SEM),energy spectrometer,glow analyzer(GDS),and three-di-mensional morphology instrument(3D-OM),the causes of frequent dark spot defects in the production process of hot-dip galvanized Si-Cr series high strength steel in a factory were systematically analyzed.The results showed that the main causes of the dark spot defects were the uneven surface of galvanized sheet,the fluctuation of zinc layer,and the uneven surface enrichment of Si and Cr elements in the substrate.The unreasonable control of morphology and microstructure of oxide scale in hot rolling raw materials provided the conditions for the formation of dark spot defects.Through the adjustment of hot roll-ing coiling and cooling system,the structure and surface microstructure of the oxide scale could be improved,which effec-tively avoided the occurrence of dark spot defects.
Si-Cr high strength dual phase steeldark spot defectelement enrichmentcoiling process
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