What is it?

A caster fold appears as a very fine, jagged crack parallel to rolling direction, and can only be seen after pickling. This defect is also called a longitudinal crack, or a longitudinal face crack. It is caused as a result of uneven heat removal from the steel shell as it is solidifying in the mold during the casting process. When solid material builds up inside the casting mold, it will leave a groove in the slab. When the slab is rolled to final gauge, the groove closes up into a tight crevice or crack.  It is more common on certain grades and on heavier gauges, which don’t allow enough reduction to remove it.

Caster Fold