Specifying finishes for stainless steel flat products (sheet and plate)

Introduction

Surface finishes for stainless steel sheet (coil, strip) and plates, are specified in BS EN 10088-2:2005. 'Stainless steels - Technical delivery conditions for sheet/plate and strip of corrosion resisting steels for general purposes.'
The standard identifies both 'ex-mill' hot and cold rolled finishes and 'special finishes', as value added finishes to achieve specific aesthetic effects.

Most of the finishes available have a surface that provides a high standard of corrosion resistance, up to the limit of the compositional potential of the particular grade.
The coarser finishes (eg finish 'G') may limit the corrosion resistance of the steel in severe applications, where the particular grade is operating in conditions close to the limit of its corrosion resistance.
In numeric or quantitative terms this is very difficult to define and is often a matter of judgement.

See Euroinox publication The Mechanical Finishing of Decorative Stainless Steel Surfaces for further information.

BS EN 10088-2 surface finishes

Table 6 of BS EN 10088-2 defines finishes for both

  • Ex-mill Hot Rolled Finishes (1)
  • Ex-mill Cold Rolled Finishes (2)
  • 'Special Finishes'

 

The definitions of surface finish do not attempt to express surface finish in terms of the surface topography achieved in terms of Ra values.
The standard uses a coding system based on the manufacturing process.
A full definition is shown in the standard, with appropriate notes in terms of: -

  • Type of process route
  • Surface finish

 

To precisely define a 'special finish' for a particular application where a specific aesthetic texture or appearance is required usually involves close consultation with specialist finishers, as surface characteristics can vary.
Once the grade of finishing grit has been defined, the final acceptance of special finishes is often done by using reference 'swatch' samples.

Ex-mill hot rolled finishes

The table shows the BS EN 10088-2 hot rolled finishes from table 6 of the standard, with a guide to typical Ra values (in micro-metres) , based, where available, on manufacturers or surface finishing contractors' data.

Ex-mill Hot Rolled Finishes
Abbreviation Finishing Process Route Notes Typical (Ra) micro-metres
1C Hot rolled, heat treated, not descaled Surface covered with mill scale. Finished parts may be suitable for heat (oxidation) resisting applications as supplied, but should be descaled to optimise corrosion resistance .
1E Hot rolled, heat treated, mechanically descaled Free of mill scale by shot blasting or grinding. This finish can also limit the crevice corrosion resistance .
1D Hot rolled, heat treated, pickled Most common 'hot rolled' finish available. Most corrosion resistant hot rolled finish specified 4-7
 
1U Hot rolled, not heat treated, not descaled Surface is left covered with rolling (mill) scale. Surface suitable for products intended for further working eg strip for re-rolling. -

Ex-mill cold rolled finishes

The table shows the BS EN 10088-2 cold rolled finishes from table 6 of the standard, with a guide to typical Ra values (in micro-metres) , based, where available, on manufacturers or surface finishing contractors' data.

Ex-mill Cold Rolled Finishes
Abbreviation Finishing Process Route Notes Typical (Ra) micro-metres
2B Cold rolled, heat treated, pickled, skin passed Most common 'cold rolled' finish available. Non-reflective, smooth finish, good flatness control. Thickness range limited by manufactures' skin passing rolling capacity. 0.1-0.5
2C Cold rolled, heat treated, not descaled Smooth with scale from heat treatment, suitable for parts to be machined or descaled in subsequent production or where the parts are for heat resisting applications. -
2D Cold rolled, heat treated, pickled Thicker sheet size ranges. Smoothness not as good as 2B, but adequate for most purposes. 0.4-1.0
2E Cold rolled, heat treated, mechanically descaled Rough and dull. Usually applied to steels with a scale which is very resistant to pickling solutions -
2H Cold rolled, work hardened "Temper" rolling on austenitic types improves mechanical strength. Smoothness similar to 2B -
2R Cold rolled, bright annealed Highly reflective "mirror" finish, very smooth. Often supplied with plastic coatings for pressings. Manufactured items usually put into service without further finishing .05-0.1
2Q Cold rolled, hardened and tempered, scale free Only available on martensitic types (eg 420). Scaling avoided by protective atmosphere heat treatment or descaling after heat treatment -

Special finishes

The table shows the BS EN 10088-2 special finishes from table 6 of the standard, with a guide to typical Ra values (in micro-metres) , based, where available, on manufacturers or surface finishing contractors' data.

 

Special Finishes
Abbreviation Finishing Process Route Notes Typical (Ra) micro-metres
1G or 2G Ground Can be based on either '1' or '2' ex-mill finishes. A unidirectional texture, not very reflective -
1J or 2J Brushed or dull polished Can be based on either '1' or '2' ex-mill finishes Smoother than "G" with a unidirectional texture, not very reflective 0.2-1.0
1K or 2K Satin polished Can be based on either '1' or '2' ex-mill finishes Smoothest of the special non-reflective finishes with corrosion resistance suitable for most external applications. less than0.5
1P or 2P Bright polished Can be based on either '1' or '2' ex-mill finishes Mechanically polished reflective finish. Can be a mirror finish. less than 0.1
2F Cold rolled, heat treated, skin passed on roughened rolls Uniform non-reflective matt surface, can be based on either 2B or 2R mill finishes -
1M or 2M Patterned Can be based on either '1' or '2' ex-mill finishes. One side patterned only. Includes "chequer" plates ("1" ex-mill finish) & fine textures finishes ("2" ex-mill finish) -
2W Corrugated Profile rolled (eg trapezoidal or sinusoidal shapes) -
2L Coloured Applied to flat (2R, 2P or 2K type fishes) or patterned (2M) sheet base finishes in a range of colours -
1S or 2S Surface coated Can be based on either '1' or '2' ex-mill finishes . Normally coated on one side only with a metallic coating, such as tin, aluminium or titanium -

Electropolished finishes are not covered in BS EN 10088-2 table 6. The process is however covered by BS ISO 15730 and is outlined in the technical article Electropolishing of stainless steels
Shot blast, shot peen and glass bead peening surface finish processes are not covered by BS EN 10088-2 table 6. There is no British Standard that specifically deals with specifying these finishes on stainless steels. US Military Specification MIL-S-13165 is used by some contract finishers for specifying the control of shot peening of metal parts.

See http://www.euro-inox.org/fla_240_EN.html for examples of finishes.

Comparison of current surface finish codes with BS 1449 (obsolete)

The table gives an indication of how different surface finish specifying systems define similar finishes, in relation to BS EN 10088-2.

- Description BS1449-2 DIN ASTM (A480)
1D Hot rolled, heat treated, pickled 1 IIa (c2) 1
2B Cold rolled, heat treated, pickled, skin passed 2B IIIc (n) 2B
2D Cold rolled, heat treated, pickled 2D IIIb (h) 2D
2R Cold rolled, bright annealed 2A IIId (m) BA
2G Cold rolled, ground 3A - No.3
2J Cold rolled, brushed or dull polished 3B (or 4) - No.4
2K Cold rolled, satin polished 5 - No.6
2P Cold rolled, bright polished 8 - No.8

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