STAINLESS STEEL PRODUCT FINISHES

No 1 finish:  Hot rolled, annealed and de-scaled by acid pickling and/or shot blasting.

No 2D finish:  This finish is produced by cold rolling, annealing and pickling.  The dull finish is imparted by having the de-scaling as a final operation or by a light skin pass with dull rolls.  This dull finish offers a more open surface to hold forming lubricants, somewhat better ductility because of less work hardening in the cold rolled temper (skin) pass, and some economies for mill designated commodity products. such as pipe, tube and reroll.  Caution should be exercised in using this product where mechanical polishing will be required, where flatness and shape is critical, or where appearance uniformity is expected in traditional 2B applications.

No 2B finish:  This most commonly specified finish is produced by giving the 2D finish a light cold pass on polished rolls.  This operation closes the surface, enhances the shape and flatness and slightly elevates the mechanical properties.

No 3 polished finish:  A mechanical finish produced by grinding the stainless with one or a sequence of abrasive belts much like sandpaper. The industry standard definition of a #3 finish states that the final operation is performed with a 100 grit belt. (see notes below).

No 4 polished finish:  A finer finish than #3 achieved with abrasive belts approximately 120-150 grit.  (see notes below)

NOTES:  Unfortunately, the industry definitions of the above finishes describe processes, not the final results.  The best way to determine the finish you require is to: 1)  Pick the finish you or your customer like and require. 2) determine the profilometer reading of the surface (a profilometer is an instrument that measures the surface profile, peaks and valleys, of the polished finish expressed as RA values) and develop +/- tolerances that are within the process limits.   Typically, a number 3 finish is an RA 30 nominal, +/- 15 RA values and a number 4 finish is a RA nominal 20 +/- 10.   Achieving the end result on a consistent basis requires a good polishing source with good measuring equipment and developed practices – belt sequences and composition to achieve the desired result.

A backpass (the polished finish on the backside of the sheet) is often specified when a part of the back surface is exposed to the eye (aesthetics) or if an adhesive is to be applied to bond the sheet to another surface.  Be sure your customer wants a backpass and is not looking for a two sided polished finish.  The backpass finish will be similar to the prime but not an exact match.  It is important to communicate to your supplier if a backpass is required or if it is not wanted.  A backpass is generally applied in the production sequence with a single belt facing the back of the sheet.  Some polishers require a backpass when polishing lighter gauges (<.024) to avoid heat distortion from the topside polishing operation.  Be sure to tell your supplier how critical the backpass is.  “Edge to Edge” backpass is a known standard for the quality of the finish which can be compromised by poor shape and/or heavy burr.

Rolled on Finish:  Most mills can produce a rolled on finish.   It involves polishing temper mill rolls with the desired finish look and then rolling a bright annealed substrate coil to the finish on the temper mill rolls. Some mills claim the rolled on finish produces a finer surface profile which minimizes the electrolytic cell effect over coarser, mechanically produced finishes.  Electrolytic cell effect is a key component in the corrosion process.  Because the steel is rolled between two similar rolls you get a backpass – like it or not.

Bright Annealed:  Any steel will look like the roll it was produced on coming off the mill.  Dull roll = dull steel, bright roll = bright steel.  Bright annealed finishes are produced in the same way as the 2B finish except they are cold reduced and temper passed on highly polished rolls 400 – 600 grit.   These coils are then annealed in furnaces that have an inert atmosphere (argon, hydrogen, cracked ammonia) to preserve the bright finish.  The bright annealing process usually calls for more cold reduction than the 2B finish to enhance the surface quality.

No 7 finish:  Can be produced by grinding and buffing either 2B or BA sheet or coil.  This is a mirror like finish with some abrasive grit lines visible in the background.  This coil can be produced by coil or sheet processing.  This finish is often referred to as Buff or Pre-Buff.

No 8 finish:  Same as No 7 finish except there are no background lines.  Almost exclusively produced by a sheet process.

No 6 finish:  A dull, architectural finish produced by tampico brushing a #4 finish.  While it is a dinosaur, it is still specified on occasion.  Get a sample and let Taunton figure it out.

STRIP FINISHES:
Are the same as the sheet finishes but nomenclature is a bit different.