Inherent discontinuities in a raw material that run longitudinally. They are folds in the material, not fractures at the grain boundary.
A surface defect caused during the steel making process. Seams are generally formed from blow holes in the ingot, non metallic inclusions, or stresses arising during the solidification stage. They appear as longitudinal discontinuities in the bar.
A narrow, non-crystalline discontinuity, which is usually inherent in the raw material. Seams are usually straight or smooth-curved line discontinuities running parallel to the product axis.