Based on a model of microstructure evolution, an appropriate rolling schedule
has been worked out to produce ultrafine grained steel (2 to 5 μm) on the hot strip mill.
This rolling schedule is characterized by a large reduction in the finishers followed by
strong cooling. Implementing such a rolling schedule on a conventional HSM raises major
problems: increased rolling torque and force, lowered crown and shape control, disturbed
looper control, accelerated roll damage, increased slip between strip and roll,
insufficient cooling efficiency. These problems have been solved on the new Nakayama
HSM by introducing innovative processes such as: single roll drive with different
diameter and a new CVC, curtain wall cooling in the finisher, low inertia hydraulic looper,
new high-speed steel rolls with solid lubrication.