Surface Defects On Slab In Chongsteel And Its Behavior During Rolling

Subject to the limitations of the production conditions and other factors, it isdifficult to achieve a completely defect-free slab continuous casting. To guarantee thequality of the rolled billet, surface defects on the slab shall be cleaned, therebyincreasing the occupied space and labor workload, at the same time improve the cost ofproduction. Therefore, understanding the formation mechanism and the evolution ofslab surface defects during the rolling process has an important practical significance toreduce the amount of slab defects, optimize the process and improve productionefficiency.In this paper, investigations on the type, distribution and frequency of major slabsurface defects were carried out in Chongsteel. The evolution and its influencing factorsin the deformation of surface defects during rolling were studied by comparison sitetracking, microscopic analysis and detection, simulation and other means. Themechanism on the defects healing during rolling was analyzed. The conclusions are asfollows:①In Chongsteel, the main surface defects on slab were transverse coner crack，surface pits, blowhole, depression and longitudinal crack. During rolling, surface pitsand blowhole on the slab can be healing, depression can be partially healing, whilelongitudinal crack can’t be healing. Thereby, the slab surface defects cleanup standardswere made.②Experimental study on high temperature mechanical properties of typical slabwas carried out to point out the low plasticity zone of the steel, thereby reducing theslab surface cracks in Chongsteel.③The source of steel crack and the mechanism of its generation and propagationwere pointed out by observing the microstructure of the crack with metallographicmicroscope and electron microscope.④Simulation studies in the evolution of surface defects during rolling werecarried out to point out its relationship between the initial morphology and size ofdefects, compression ratio and other factors. The mechanism on surface defects healingduring rolling was discussed.