Original Article

Formation mechanism of surface upwarping and black line defects on low carbon hot rolled plate

¹ Hebei High Quality Cold Heading Steel Innovation Technology Center, School of Materials and Science Engineering, Hebei University of Engineering, Handan 056000, Hebei, China
² School of Marxism, Handan University, Handan 056000, Hebei, China
³ Warwick Manufacturing Group, University of Warwick, Coventry CV4 7AL, UK

^* e-mail: zhaos418@hebeu.edu.cn

Received: 4 March 2023
Accepted: 1 June 2023

Abstract

To improve the surface quality of low-carbon hot-rolled steel plates, the upwarping and black line defects were investigated by means of XRF (X-ray diffractometer), OM (optical microscopy), SEM (scanning electron microscopy) and EBSD (electron back scatter diffraction). The results showed that the micro area compositions under surface upwarping and black line defects were mainly made of secondary oxide particles, steelmaking slag and mould flux respectively. According to the metallographic structure, inclusion compositions and grains texture analysis, it could be concluded that surface defects on hot rolled plates were attributed to the entrapment of ladle slag or mould flux, gas bubbles, micro-cracks of casting slab in the steelmaking process, rolled-in scale and unreasonable sizing press rolling parameters during the rolling process, and the position and formation process of typical surface defects on hot rolled plates were discussed in detail. Finally, it concluded that the slag entrapment and solidification hook should be controlled during continuous casting.