Abstract: The abnormal microstructural banding at centerline was compared among three steel plates of 355 MPa grade using OM， TEM and EPMA， and the effects of ultrafast cooling (UFC) and finish rolling temperature (FRT) were discussed. It was found that UFC was effective to suppress banding in centerline segregation zones， as the bands were entirely disappeared in UFC steel with FRT at 950℃ (UC1 steel)， comparing with the feeble bands in UFC steel with FRT at 900℃(UC2 steel). In contrast， severe bands consisting of martensite/austenite constituent (M/A) were observed in a conventional laminar-water cooled steel (LC steel)with a cooling rates of 15℃/s. The thermodynamic calculation showed that the equilibrium temperature of austenite-to-ferrite transformation could be reduced by 144℃ in elements-rich centerline zone， increasing the critical cooling rate to 8℃/s for avoidance of banding. The simulated temperature indicated the cooling rate of 12.1 and 13.4℃/s at the mid-thickness of UC1 and UC2 steels， respectively， comparing with that of 5.5℃/s for LC steel. Therefore， UFC provides sufficient cooling capability for suppressing microstructural banding at plate centerline， while the lower FRT could offset the effect. In contrast， banding cant be prevented by exploring laminar-water cooling because of its relatively low cooling rate.

Key words: ultrafast cooling, finish rolling temperature, microstructural banding at centerline, chemical segregation, critical cooling rate