Abstract: During hot rolling of dual phase steels, unstable coiling temperatures were observed with coiling temperature fluctuations greater than 150°C below the target. The low coiling temperature areas corresponded to dark scale stripes on the steel surface, linked to rewetting on the runout table. The hot band microstructure in dark scale areas was tempered martensite, whereas the hot band microstructure in areas with the normal surface appearance was a mixture of bainite, ferrite and pearlite. Higher yield and tensile strengths were also observed in dark scale areas. Localized fluctuations in hot band properties can potentially cause problems in cold rolling including gauge hashing, shape issues and strip breaks. Therefore, these low coiling temperature areas were cropped out creating large yield losses. Adjusting the target coiling temperature reduced the occurrence of low coiling temperature fluctuations caused by rewetting, thereby avoiding the need for regular cropping and reducing yield losses.
Authors:E.M. Bellhouse, A. J. Silvestri, and E. A. Ianos
Keywords: Dual Phase Steel, Hot Rolling, Rewetting, Oxide Scale, Mechanical Properties