Forging squeezes the slag out, thereby purifying the steel. As far as I am aware this was the primary mechanism by which folding steel (which was done about a

Forging squeezes the slag out, thereby purifying the steel. As far as I am aware this was the primary mechanism by which folding steel (which was done about a dozen times, not hundreds; those larger numbers come from 2^[n folds]) strengthened Japanese blades.