1.Very small, like sand or salt and shallow in depth
2.Over all or band distribution
3.More carbon, more frequent
4.The higher temperature, the more frequent

1.Deteriorated roll surface in F1-F4
2.High rolled stock temperature in F1-F4

1.Rolling load should be decreased
2.Temperature in F1-F4 should be decreased.
3.HSS roll can reduce the problem
4.Adoption of lubrication rolling
5.Change BUR, if it is deteriorated