Stainless steel surface treatment methods are numerous, including polishing, brushing, pickling, and sandblasting, each affecting the appearance, performance, and applicability of the stainless steel. The variety of surface treatment methods can lead to difficulties in selection.
What is finish of stainless steel
The finish of stainless steel refers to the surface treatment applied to the material, which affects its appearance, corrosion resistance, and suitability for specific applications.
Common stainless steel finishes include No. 1 (hot-rolled, dull), No. 2D (cold-rolled, smooth), No. 2B (cold-rolled, bright), bright annealed (reflective), No. 3 (polished with linear texture), No. 4 (general-purpose polished), No. 6 (dull satin), No. 7 (high luster), No. 8 (mirror finish), and TR (cold-worked to enhance properties).
Description of stainless steel surface treatment in ASTM standards
No. 1 Finish: Commonly referred to as hot-rolled, annealed, and pickled or descaled. This is a dull, non-reflective finish.
No. 2D Finish: A smooth, non-reflective cold-rolled annealed and pickled or descaled finish. This nondirectional finish is favorable for retention of lubricants in deep drawing applications.
No. 2B Finish: A smooth, moderately reflective cold-rolled annealed and pickled or descaled finish, typically produced by imparting a final light cold-rolled pass using polished rolls. This general-purpose finish is more readily polished than No. 1 or No. 2D finishes. Product with 2B finish is normally supplied in the annealed plus lightly cold-rolled condition unless a tensile-rolled product is specified.
Bright Annealed Finish: A smooth, bright, reflective finish typically produced by cold rolling followed by annealing in a protective atmosphere to prevent oxidation and scaling during annealing.
No. 3 Finish: A linearly textured finish that may be produced by either mechanical polishing or rolling. Average surface roughness (R) may generally be up to 40 μin. A skilled operator can generally blend this finish. Surface roughness measurements differ with different instruments, laboratories, and operators. There may also be overlap in measurements of surface roughness for both No. 3 and No. 4 finishes.
No. 4 Finish: A linearly textured finish that may be produced by either mechanical polishing or rolling. Average surface roughness (R) may generally be up to 25 μin. A skilled operator can generally blend this finish. Surface roughness measurements differ with different instruments, laboratories, and operators. There may also be overlap in measurements of surface roughness for both No. 3 and No. 4 finishes.
No. 6 Finish: This finish has a soft, satin appearance typically produced by tampico brushing a No. 4 finish.
No. 7 Finish: Has a high degree of reflectivity. It is produced by buffing a finely ground surface, but the grit lines are not removed. It is chiefly used for architectural or ornamental purposes.
No. 8 Finish: This is a highly reflective, smooth finish typically produced by polishing with successively finer grit abrasives, then buffing. Typically, very faint buff or polish lines may still be visible on the final product. Blending after part assembly may be done with buffing.
TR Finish: The finish resulting from the cold-rolling of an annealed and descaled or bright annealed product to obtain mechanical properties higher than that of the annealed condition. Appearance will vary depending upon the starting finish, amount of cold work, and the alloy.
Architectural Finishes: Sometimes described as a No. 5 finish, these are a separate category and may be negotiated between buyer and seller, as there are many techniques and finish variations available throughout the world.
Description of stainless steel surface treatment in EN DIN standards
| Type of process route and surface finish of sheet,plate and strip【a】 | ||||
| Symbol【b】 | Type of process route | Surface finish | Notes | |
| Hot rolled | 1U | Hot rolled,not heat treated,not descaled | Covered with rolling scale | Suitable for products which are to be further worked e.g.strip for rerolling. |
| 1C | Hot rolled,heat treated, not descaled | Covered with rolling scale | Suitable for parts which will be descaled or machined in subsequent production or for certain heat-resisting applications. | |
| 1E | Hot rolled,heat treated, mechanically descaled | Free of scale | The type of mechanical descaling,e.g coarse grinding or shot blasting, depends on the steel grade and the product,and is left to the manufacturer’sdiscretion,unless otherwise agreed. | |
| 1D | Hot rolled,heat treated, pickled. | Free of scale | Usually standard for most steel types to ensure good corrosion resistance;also common finish for further processing.It is permissible forgrinding marks to be present.Not as smooth as 2D or 2B. | |
Cold rolled | 2H | Work hardened | Bright | Cold worked to obtain higher strength level |
| 2C | Cold rolled, heat treated,not descaled | Smooth with scale from heat treatment | Suitable for parts which will be descaled or machined in subsequent production or for certain heat-resisting applications. | |
| 2E | Cold rolled, heat treated,mechanically descaled | Free of scale | Usually applied to steels with a scale which is very resistant to pickling solutions. May be followed by pickling. Surface roughness is depending on the mechanical descaling method and may differ if the surface is e.g.shot blasted or brushed. | |
| 2D | Cold rolled, heat treated,pickled | Smooth | Finish for good ductility,but not as smooth as 2B or 2R. | |
| 2B | Cold rolled, heat treated,pickled,skin passed | Smoother than 2D | Most common finish for most steel types to ensure good corrosion resistance,smoothness and flatness.Also common finish for further processing.Skin passing may be by tension levelling | |
| 2A | Cold rolled, heat treated,bright-pickled, skin passed | Smoother and more reflective than 2D | Typical finish for ferritic grades when high reflectivity is desired. | |
| 2R | Cold rolled, bright annealed【c】 | Smooth, bright, reflective | Smoother and brighter than 2B.Also common finish for further processing. | |
| 2Q | Cold rolled,hardened and tempered,scale free | Free of scale | Either hardened and tempered in a protective atmosphere or descaled after heat treatment | |
| Special finishes | 1G or 2G | Ground【d】 | See Footnote【e】 | Grade of grit or surface roughness can be specified. Unidirectional texture, not very reflective. |
| 1J or 2J | Brushed【d】 or dull polishe【d】 | Smoother than ground. See Footnote【e】 | Grade of brush or polishing belt or surface roughness can be specified. Unidirectional texture, not very reflective. | |
| 1K or 2K | Satin polish【d】 | See Footnote 【e】 | Additional specific requirements to a “J” type finish, in order to achieve adequate corrosion resistance for marine and external architectural applications.Transverse Ra < 0,5 μm with clean cut surface finish | |
| 1P or 2P | Bright polished【d】 | See Footnote 【e】 | Mechanical polishing. Process or surface roughness can be specified. Non-directional finish, reflective with high degree of image clarity. | |
| 2F | Cold rolled, heat treated, skin passed on roughened rolls | Uniform non reflective matt surface | Heat treatment by bright annealing or by annealing and pickling. | |
| 1M | Patterned | Design to be agreed; 2nd surface flat | Chequer plates used for floors. | |
| 2M | A fine texture finish mainly used for architectural applications. | |||
| 2W | Corrugated | Design to be agreed | Used to increase strength and/or for cosmetic effect. | |
| 2L | Coloured | Colour to be agreed | ||
| 1S or 2S | Surface coated | Coated with e.g. tin, aluminium | ||
| 【a】Not all process routes and surface finishes are available for all steels. 【b】 First digit: 1 = hot rolled, 2 = cold rolled. 【c】 May be skin passed. 【d】 One surface only, unless specifically agreed at the time of enquiry and order. 【e】 Within each finish description the surface characteristics can vary, and more specific requirements may need to be agreed between manufacturer and purchaser (e.g. grade of grit or surface roughness). | ||||
The similarities between ASTM and EN standards regarding stainless steel finishes.
| Designation ASTM(EN) | Description |
| No. 0 | Hot-rolled, annealed, thicker plates |
| No. 1 (1D) | Hot-rolled, annealed, and passivated |
| No. 2D (2D) | Cold rolled, annealed, pickled, and passivated |
| No. 2B (2B) | Same as above with additional pass through polished rollers |
| No. 2BA (2R) | Bright annealed (BA or 2R) under oxygen-free conditions |
| No. 3 (G-2G) | Coarse abrasive finish applied mechanically |
| No. 4 (1J-2J) | Brushed finish |
| No. 5 | Satin finish |
| No. 6 (1K-2K) | Matte finish (brushed but smoother than #4) |
| No. 7 (1P-2P) | Reflective finish |
| No. 8 | Mirror finish |
| No. 9 | Bead blast finish |
| No. 10 | Heat colored finish – a range of electropolished and heat colored surfaces |
Why is it important to understand stainless steel surface treatment methods?
The importance of understanding stainless steel surface treatment methods can be summarized in the following aspects:
Performance Optimization: Different surface treatment methods can significantly enhance the corrosion resistance, wear resistance, and antibacterial properties of stainless steel, thereby extending its service life and maintaining its performance.
Applicability: Certain applications have specific requirements for the surface of stainless steel. For instance, the food and medical industries require non-porous and easy-to-clean surfaces, while architecture and decoration focus more on aesthetics. Therefore, understanding surface treatment methods helps in selecting suitable materials.
Maintenance and Care: Different surface treatments have varying maintenance requirements. Understanding these differences can aid in developing effective maintenance plans to ensure the long-term performance of stainless steel products.
Cost Control: The costs of different surface treatments vary. Understanding these can facilitate more economical choices during procurement, especially in large-scale applications.
Market Competitiveness: For manufacturers and suppliers, understanding stainless steel surface treatment technologies can help offer more competitive products that meet market demands.
In summary
Understanding stainless steel surface treatment methods enables users to make more informed decisions when selecting and using stainless steel, enhancing the overall performance and economic benefits of the materials.
More information about finish of stainless steel
