Metallurgical investigations into the genesis of bare spots, exfoliation, and matte coating appearance in hot dip galvanized steel sheets
Continuously processed hot dip galvanized steel sheets that exhibited bare spots, exfoliation/peel-off, and matte coating appearance were investigated to gain an insight into the genesis of such defects. Scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS) and electron probe microanalysis (EPMA) were employed in conjunction with analysis of the galvanizing bath. Analyses revealed a bath condition sensitive to surface cleanliness of the steel substrate and showed significant levels of carbonaceous residues and rolling debris on the annealed steel substrates. This improper steel surface condition has been attributed to excess oil carry-over on the cold rolled strip surface and poor burnoff in the annealing furnace.
Keywordsbare spots bath analysis EPMA exfoliation hot dip galvanized coating matte appearance SEM/EDS
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- 1.N.Y. Tang and F.E. Goodwin: “A Study of Defects in Galvanized Coatings,” Proc. of Fifth Int. Conf. on Zinc and Zinc Alloy Coated Steel Sheet, M. Lamberights, ed., Galvatech 2001, June 26–28, 2001 (Brussels, Belgium), Verlag Stahleisen, Düsseldorf, Germany, pp. 49–55.Google Scholar
- 2.E.V. Proskurkin and N.S. Gorbunov: Galvanizing, Sherardizing and Other Zinc Diffusion Coatings, Technicopy Limited, Gloucestershire, England, in association with Zinc Development Association, London, 1975, pp. 96–107.Google Scholar