Abstract:The samples of cold-rolled sheets, hot-rolled plates and continuously cast slabs have been analyzed with the condition of faint-sliver defects appeared in IF steel of Pangang, and it was shown that faint-sliver defects in cold-rolled steel sheet were mainly caused by micro-cracks in the surface of strands, slag entrapment in mold during casting and inclusions in sub-surface of strand. Faint-sliver defects were controlled effectively with the technical measures, which were decreasing oxidation of ladle slag, co… Show more
“…Moreover, this sort of inclusion was not expected in these examined surface defects because of the constant casting speed during ladle changes. It is known from the literature [25,26] that the variation in casting speed may influence the increase of mould flux entrapment on slabs. Figure 3. Intact macro-inclusion from slab sample.…”
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.
“…Moreover, this sort of inclusion was not expected in these examined surface defects because of the constant casting speed during ladle changes. It is known from the literature [25,26] that the variation in casting speed may influence the increase of mould flux entrapment on slabs. Figure 3. Intact macro-inclusion from slab sample.…”
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.
“…In the hot-dip galvanising process of automobile exposed panels, the presence of inclusions or entrained mould fluxes on the steel substrate will usually result in surface defects to occur more obviously after the hot-dip galvanising process [1]. The major causes of sliver defects caused by steelmaking are macro Al 2 O 3 inclusions, entrained mould fluxes and argon bubbles with Al 2 O 3 inclusions [2][3][4][5][6]. In particular, the entrained mould fluxes are large in the size and close to the slab surface, which is very easy to form serious surface defects in the process of rolling and hot-dip galvanising.…”
The characteristics of sliver defects caused by entrained mold fluxes were analyzed after nonaqueous electrolysis. There are three types of entrained mold fluxes, namely the granular, flaky and blocky. When the entrained mold fluxes are small, they are granular or flaky. When the entrained mold fluxes are large, they are blocky or flaky. From the start part of the defect zone, the area fraction of the entrained mold fluxes per unit area decreases exponentially with the length of defect. After the mold fluxes are entrained into the molten steel, SiO 2 will react with Al and Ti, resulting in the changes in compositions of mould powders. On the cross-section, the zinc layer thickness in the defect zone, is 22-35 μm, thicker than that in the non-defect zone. Near the entrained mold fluxes, the randomness of grain orientation and the inhomogeneity of grain size are increased and the local grains are refined.
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