Sliver defects in an ultra-low carbon Al-killed steel caused by low steel level in the tundish

Abstract

Sliver defects were detected in galvanized and uncoated cold-rolled strips, and their causes were investigated. Most of these strips were produced from transition ladle slabs, which were obtained in a sequence of twenty heats of an ultra-low carbon Al-killed steel. A significant reduction in the steel level in tundish occurred during these slabs' casting. The strip defects, and as a comparative, a mould flux inclusion found in a first slab of the sequence, were analysed with a scanning electron microscope (SEM). Also, each of the twenty heats was sampled in tundish, quenched in water, and manually analysed with SEM to characterize its dominant inclusions. Regarding the sliver defects, mainly silica together with alumina or Al-Ti-O systems particles were found in them. The primary sources for these particles are likely tundish flux and reoxidation products. Finally, a mechanism was proposed for the formation of these inclusions.

Characteristics of sliver defects caused by mould flux entrainment on the surface of the hot-dip galvanised automobile exposed panel

“…Dhua [16] analysed the defect samples after acid etching with OM and SEM–EDS, and believed that the entrained mould flux particles and inclusions will cause local weakness on the surface of the hot rolled plate, and the failure zone will form dents or strip defects on the surface of the cold rolled sheet in the subsequent cold rolling process. Leao et al [17] used SEM to analyse the sliver defects on the surface of hot-dip galvanised and cold rolled sheets. By comparing the inclusions with the tundish flux, it was pointed out that silica macro-inclusions containing Al 2 O 3 or Al–Ti–O in the defect zone has led to sliver defects on the surface of hot-dip galvanised and cold rolled sheets.…”