Occurrence of Coarse Grains in Hot-rolled Low Carbon Aluminium Killed Steel Sheets Coiled at High Temperature

Abstract

The occurrence of coarse grains in hot-rolled low carbon aluminium-killed steel sheets coiled at high temperature was studied.
The relation between microstructures and hot rolling conditions was investigated on the basis of hot rolling experiments in the laboratory.
Fine grain bands form by finish-rolling below the Ar₃ temperature, and they change to coarse grain bands by abnormal grain growth. They form at the surface of sheet when the finishing temperature is close to Ar₃, and extend to its center in thickness with lowering the finishing temperature.
Aluminum nitride begins percipitating rapidly at grain boundaries after finish-rolling. This compound is the main precipitate pinning grain boundary. But the abnormal grain growth proceeds mostly before the grain boundaries are pinned firmly by the precipitation of AIN.
These results were confirmed in the hot rolling experiments in the shop.