SUN Hao, LI Zhaoyang, ZHANG Liying, CUI Heng, LI Hongjun, HUANG Zhi, CHEN Yexiong, WANG Kang
To explore the causes of sliver defects on the surface of SPHC hot rolled plates produced by the third generation thin slab continuous casting and rolling technology in a factory, a comprehensive analysis was conducted. Samples of the SPHC hot rolled plates were collected, and both the morphology and composition of the defect surfaces and cross sections were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and large sample electrolysis. The study revealed that the primary components of the inclusions at the defect sites were CaO-SiO2-Al2O3-MgO-Na2O composite inclusions and Al2O3 particles. The presence of CaO-SiO2-Al2O3-MgO-Na2O composite inclusions is attributed to mold slag entrainment, while the Al2O3 particles are likely a result of secondary oxidation of molten steel and nozzle clogging. Additionally, an analysis of the slab quality produced under identical process conditions was performed. Following slime electrolysis of the slab, it was determined that the major composition of large inclusions in the slab was Ca-Al-O. Out of 131 large inclusions extracted, 13% were primarily composed of Ca, Al, Si, Mg, K, and Na, supporting the hypothesis that these inclusions also arise from mold slag entrainment. Furthermore, 31.8% of the large inclusions contained more than 10% of elements such as Nb, Mo, Ni, and W. These elements are believed to originate mainly from scrap or alloy additions during the steelmaking or refining process prior to continuous casting, with the high content potentially due to ladle slag involvement during pouring. In conclusion, the research identified mold slag entrainment and secondary oxidation as significant contributors to the sliver defects on SPHC hot rolled plates.