Analysis of Transverse Corner Cracks of Microalloyed Steel and the Countermeasures

by Chih-Yuan Chen, Kuan-Ju Lin, Chun-Hung Wu, Chi-Lun Kao

Publisher - China Steel Corporation, Taiwan

Category - General Novel

Transverse corner crack is a severe defect detected on hot-rolled billets of microsalloyed steel. The aim of this paper is to study the formation mechanism and the influence of process parameters on this defect formation. The microstructure investigation had revealed that the defects were attributed to transverse cracks occurring at bloom corners. Transverse corner cracks initiated and developed along γ grain boundaries while the blooms were subjected to an improper composition and casting process. Precipitation of AlN, BN at γ-grain boundaries resulted in ductility loss, which enhanced crack formation. Higher Ti content promoted TiN precipitation, and restrained AlN, BN to form at higher temperature than the straightening point. Soft secondary cooling was also applied to increase corner temperature and reduce temperature fluctuation. The defect rate was dramatically reduced from > 30% to < 2% after the countermeasures were applied.

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