On the Occurrences of “Frizzle-Type” Surface Defects in a Hot-Rolled Steel Plate
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Metallurgical investigations were directed to probe into the genesis of “frizzle” and fissure-type surface defects on 10-mm hot-rolled steel plates meant for application in flat-bed wagons for carrying heavy machinery. The thin hairline fissures on the steel plates were identified as skin laminations associated with long, shallow, and branched cracks, intruding from the plate surfaces to the interior with curved contours, replete with fragmented oxide scale entrapments and debris. The incidence of these superficial defects on the plates was linked to surface damage to the solidifying skin of continuously cast steel slabs, induced by the extensive pitting and cavitation of caster pinch rolls. It is presumed that during hot rolling of the steel slabs, surface blemishes like indentations and folds got rolled over by metal flow, entrapping copious amounts of primary as well as secondary scales underneath the laminated skin. Under the influence of shear forces during rolling, the defects are believed to have ingressed further into the plate interior leading to the formation of long, shallow, and branched cracks with curved contours and entrapped fragmented oxide scales.