Stainless Steel Standard Mill Surface Finish
The Standard Mill Surface Finished for stainless steel are laid down in Specifications (BS 1449, Part 4, and the Committee of Stainless Steel Producers, American Iron & Steel Institute). The stainless steel surface finishes are designated by a system of numbers, and these are broadly described hereunder relative to the finishing operations employed. It should be remembered that different grades of Stainless Steel can result in a variation of visual appearance for the same finishing operation. Stainless steel flats are supplied in the annealed ie fully softened condition.
No. 0 Finish
Also referred to as Hot Rolled Annealed (HRA). The plate is hot rolled to required thickness, and then annealed. No pickling or passivation operations are effected, resulting in a scaled black finish.
This does not develop the fully corrosion resistant film on the Stainless Steel, and except for certain high temperature heat resisting applications, this finish is unsuitable for general end uses.
No. 1 Finish Stainless Steel
Plate is hot rolled, annealed, pickled and passivated. This results in a dull, slightly rough surface; quite suitable for industrial applications which generally involve the range of plate thicknesses. Grinding marks may be visible in isolated areas.
No 2D Finish
No 2D surface stainless steel plates are suitable for industrial application, and eminently suitable for severe deep drawing as the dull surface, (which may be polished after fabrication) retains the lubricant during the drawing operation.
No. 2B Finish
Stainless steel No. 2B finish is the most common finish produced and called for on sheet material. 2B Finish is brighter than 2D and is semi-reflective. It is commonly used for most deep drawing operations, and is more easily polished to the final finished required than is a 2D finish.
BA Finish
This is more commonly referred to as a BRIGHT ANNEALED (BA) FINISH. Stainless Steel Material with a No. 1 finish is Cold Rolled using highly polished rolls in contact with the steel surface. This smooths and brightens the surface. The smoothness and reflectiveness of the surface improves as the material is rolled to thinner and thinner sizes. Any annealing which needs to be done in order to effect the required reduction in gauge, and the final anneal, is effected in a very closely controlled inert atmosphere. No oxidation or scaling of the surface therefore occurs and there is no need for additional pickling and passivating.
No. 4 Finish
No. 4 finish is a ground unidirectional finish obtained with 150 grit abrasive. It is not highly reflective, but is a good general purpose finish on components which will suffer from fairly rough handling in service (eg restaurant equipment).
No. 6 Finish
These stainless steel plates finishes are produced using rotating cloth mops (Tampico fibre, muslin or linen) which are loaded with abrasive paste. The finish depends on how fine and abrasive is used, the uniformity and finish of the original surface.