| Material selection
| Fabrication | Surface
Finishes | Cleaning
surface of Stainless Steel is actually and extremely thin
but stable and passive Chromium rich oxide film, on which
Stainless Steel relies for its excellent corrosion resistance.
The surface finish on Stainless Steel should therefore
be developed and maintained to ensure this vital property,
and also for the secondary reason of the pleasing aesthetic
appearance of Stainless Steel.
MILL FINISHED - FLAT ROLLED PRODUCTS
Standard Mill Surface Finished are laid down in Specifications
(BS 1449, Part 4, and the Committee of Stainless Steel
Producers, American Iron & Steel Institute).
finished 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. The
thickness can also have an effect, generally the thinner
the material the smoother the surface finish.
thicker gauge sizes of Stainless Steel are hot rolled.
This is done at high temperatures and will always result
in a scaled surface.
Steel Flat Product is supplied in the annealed ie fully
is also a high temperature operation and unless carried
out in a very closely controlled inert atmosphere, will
result in oxidation (scaling) of the surface.
scale is usually removed by a pickling process, that is
the removal of the scale by use of suitable acids, and
the passivated by the use of Nitric Acid.
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.
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.
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.
of the thinner thicknesses within the plate range are
Cold Rolled; but Sheet, Coil and Strip gauges are produced
by Cold Rolling, ie rolled without and heating of the
material. Cold Rolling hardens the material, and the thinner
sizes may have to be subjected to an intermediate anneal
and pickle, or bright annealed, during the reduction of
thickness to final gauge.
starting material for Cold Rolling always has a No. 1
finish. Cold Rolled material is supplied with the following
standard mill finishes.
A no. 1 Finish after being Cold Rolled, Annealed, Pickled
and Passivated. This results in a uniform dull matt finish,
superior to a No. 1 Finish.
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.
A 2D Finish is given a subsequent light skin pass cold
rolling operation between polished rolls.
is the most common finish produced and called for on sheet
material. It 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.
This is more commonly referred to as a BRIGHT ANNEALED
(BA) FINISH. 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.
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.
final surface developed can have "MIRROR" type
finish similar in appearance to the highly polished No.
7 and No. 8 Finishes.
Much of the 2B Finish sheet imported is not a true 2B
Finish. Mills which operate bright annealing facilities
will often carry out all the annealing operations of Cold
Rolled material in such facilities. This leads to a superior
"2B" finish as no oxidation or scaling takes
place during the annealing operation, even though the
actual rolling may be effected on polished rolls as for
normal 2B Finish, but not highly polished as would be
needed to produce a BA finish.
following finishes are all mechanically produced polished
finishes. As well as being standard mill finishes, they
are also applied to stainless steel articles and components
to meet the required aesthetic criteria. It should be
appreciated that factors such as hand polishing vs. mechanical
polishing; polishing a flat product as against a component
of complex shape; thickness and composition of material
can affect the visual appearance of the final surface.
This is a ground unidirectional uniform finish obtained
with 80 - 100 grit abrasive.
is a good intermediate or starting surface finish for
use in such instances where the surface will require further
polishing operations to a finer finish after subsequent
fabrication or forming.
This 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).
These finishes are produced using rotating cloth mops
(Tampico fibre, muslin or linen) which are loaded with
finish depends on how fine and abrasive is used, the uniformity
and finish of the original surface.
finish has a non-directional texture of varying reflectiveness.
"Satin Blend" is an example of such a finish.
This is a buffed finish having a high degree of reflectiveness.
is produced by progressively using finer and finer abrasives
and finishing with Buffing compounds. Some fine scratches
(grit lines) may remain from the original starting surface.
This is produced in an equivalent manner to a No. 7 Finish,
the final operations being done with extremely fine buffing
final surface is blemish free with a high degree of image
clarity, and is the true mirror finish.
The finer polished finishes (No. 4, No. 6, No. 7 and No.
8) are generally only produced one side of the sheet,
the reverse side being either a 2B or No. 3 Finish.