Analysis of surface and internal defects for continuous casting billet of 82A tire cord steel
CHEN Bo-tao1, WANG Feng-kang2, ZENG Jie2, WANG Wan-lin2, JU Yin-jun1
1. Quality Department,Xiangtan Iron and Steel Co.,Ltd., Hunan Valin, Xiangtan 411101, Hunan, China; 2. School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan,China
Abstract：The surface crack defects and central segregation of cord steel are the key factors affecting the billet quality. The macro defect analysis on the surface of billet, micro morphology characterization of crack, Gleeble high temperature mechanical properties and central segregation measurements are applied, and the surface and internal quality defects of continuous casting 150 mm×150 mm billet of 82A cord steel under steady and unsteady state are analyzed. The results show that the distance between the vibration marks of the billet is 13 mm and the vibration marks at the corners are disordered. Obvious transverse cracks are observed at the vibration mark trough and pit on the surface of unsteady billet, but no transverse cracks are appeared in the steady-state samples. Moreover, an obvious central crack with a length of 55 mm along the central shrinkage cavity in the billet is found and the average central carbon segregation index of the billet is 1.09. Based on the analysis of high temperature mechanical and cracks morphology, the appearance of surface cracks is mainly related to the straightening in the low-temperature brittle zone due to uneven cooling under the unsteady condition, The local temperature is in the third brittle temperature zone during bending and straightening. An obvious liquid film appeared on the surface of the inner central crack, which was formed at the solidification stage of the first brittle zone.
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2021, Vol. 40 
