Seams are longitudinal crevices that are tight or even closed at the surface, but are not welded shut. They are close to radial in orientation and can originate in steelmaking, primary rolling, or on the bar or rod mill.”– AISI Technical Committee on Rod and Bar Mills, Detection, Classification, and Elimination of Rod and Bar Surface Defects
Seams are longitudinal voids opening radially from the bar section in a very straight line without the presence of deformed material adjacent.
Seams may be present in the billet due to non-metallic inclusions, cracking, tears, subsurface cracking or porosity. During continuous casting loss of mold level control can promote a host of out of control conditions which can reseal while in the mold but leave a weakened surface.
In order to assure removal of unwanted seams from the bar surface, even after non destructive testing has sorted out the most non compliant bars, the customer should take adequate stock removal.
Seam frequency is higher in resulfurized steels compared to non-resulfurized grades, so stock removal recommendations for these two different kinds of steels vary.
- For non-resulfurized steels (10XX, 15XX, All Alloys) take off 0.001” per sixteenth of bar diameter per side. That means 0.032” off the diameter of a 1” diameter bar to assure seam free.
- For resulfurized steels (11XX, 12XX and 12LXX free machining steels) take off 0.0015” per sixteenth of bar diameter per side. That means 0.048” off of the diameter of a 1” diameter bar to assure seam free on resulfurized steels.
Yes that is a lot of material to remove to assure a sound seam free surface.
More info on Seams in steel.