Analysis of coil break defects

Coil breaks are narrow, irregularly changing deformation lines on low carbon steel strips. They can appear in many metallurgical manufacturing processes, such as pickling, galvanizing, cold rolling, processing on slitting or cutting lines, etc. They cause difficulties in many steel plants, since they are considered as serious surface defects leading to esthetical problems on the end product. In this paper, the types, visual appearance and microscopic properties of coil breaks are investigated. The roughness and waviness of the break lines were characterised using a contact-type surface roughness tester, while the microscopic deformation lines were studied using Hirox and Zeiss optical microscopes. The location, arrangement and relation to the microstructure can help to understand the formation mechanism of these surface defects.