The surface finish of stainless steel is a very important factor in improving the functionality as well as the appearance of the application.
The desired surface finish also has a better effect on the properties of the end product, like corrosion resistance, electrical conductivity, weldability, and manufacturing procedures.
The surface finish of stainless steel is a primary consideration in designing the products to enhance the attractive look of the end product.
Different finishes can be utilized to generate a range of visual effects in the architecture and automobile industries. For example, the stainless steel No. 4 finish is one of the most popular finishes available in everyday products, particularly kitchen appliances.
The surface finish chosen is especially significant where fabrication procedures will be used.
When the stainless steel sheets or plates are grounded before painting and bonding, rough surface treatments are suitable. Where the steel is to be mixed, smooth surface finishes are preferable.
The finished surface should always be clearly stated and correctly defined by industry standards. If you want more information about surface finishes, keep reading below article guide to learn all the types of surface finishes.
What Is A Stainless Steel Surface Finish?
The physical appearance of the stainless steel is formed through various processing procedures such as rolling, polishing, and blasting.
These finishes can vary from dull to bright; some even have specific textures that may be applied mechanically for specific uses.
Surface finish can be affected by a variety of elements, including production route, material thickness, roll surface polish, cleanliness, and mechanical abrading.
Most melt mills are capable of producing all sheets and strip finishes. While some finishes (such as BA and polished) necessitate specific lines, most mills either have these or work with a third-party processing partner.
Still, melt mills can only sometimes meet each customer’s specific Ra (surface roughness) criteria.
Some customers may need a precision re-roller to achieve their required surface finish.
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).
What Are The Different Types Of Stainless Steel Surface Finishes?
The surface finishes are categorized by the special process routing in the industry, not only the appearance of the surface.
It means surface finish can be categorized by the process or stage from which it is being passed.
There are different standards and procedures for the strips and sheets. If the dimension of the piece is more than 24 inches wide, it is called a sheet, and less than 24 inches is known as a strip.
Some common types of surface finishes are given below.
Mill Finish No. 1
This type of surface finish is known as the basic type of finish. It can be produced by hot rolling processes and used in many stainless steel products.
They are widely utilized in a variety of applications and serve as the foundation for mechanical polishing and other finishing procedures.
Most are cleaned with acid (pickled) to get rid of the scale that creates up during hot rolling and annealing to maximize corrosion resistance.
Finish No. 2B
The 2B stainless steel finish is the most common stainless steel finish.
This cold roll finish yields a smooth matte surface. It’s mostly non-reflective and smooth, with good evenness.
Following the cold rolling process, the stainless steel is annealed and pickled.
After this, 2B stainless steel is passed through “bright rolls.” This extra step gives stainless steel a distinctive smooth, flat surface.
Finish Bright Annealed (BA)
Finish the bright annealed surface obtained by the cold rolling process.
After this process, apply the annealing in a controlled atmosphere to avoid scaling.
This finish is not treated in acid since annealing produces a thin oxide film that eliminates the requirement for pickling.
This type of finish is used in trim appliances, medical tools, and cookware.
Finish Mechanically
In this type of surface finish, some abrasive tools are used, such as grinding and polishing tools, to cut the material to get the required surface finish.
Very thin and high-quality abrasive is used to polish the surface.
Polished Finish No. 3 & No. 4
Surface finish no.3 and no.4 are achieved by the brushing process.
This process consists of one-directional uniform parallel line along the length of the coil.
Finer abrasives are used to achieve a polished finish.
The range of grit abrasives is 50 to 120 for the No.3 finish and 120 to 320 for the No.4 surface finish.
Finish No. 6
Finish No. 6 is much less reflective than the No.4 finish.
It is very dull, and its color is silvery white.
This type of surface finish is a very old technique and is not commonly used on stainless steel these days.
Finish No. 8 Finish
This type of surface finish is a more reflective polished surface than all finishes recommended by the ATSM standards.
The No. 8 Finish is obtained by buffing for five to ten minutes longer than the No. 7 Finish.
The No. 8 finishes stainless steel sheets are commonly seen in high-end luxury hotels, museums, and office buildings for interior decorative applications such as panels or columns.
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 and raw materials for UV printers. | |||
| 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 |
What Is The Surface Roughness Of Stainless Steel?
The texture measurement of manufactured or polished surfaces is called surface roughness. It is the average distance between the peaks and valleys of the polished surface.
It is measured in micrometers or micro inches and written as “Ra” average roughness.
Rz, or mean roughness depth, is the average of the lowest valley to the highest peak across five sampling lengths and is most typically used in Europe.
Surface roughness can significantly impact the durability and performance of a material and must be carefully addressed and regulated.
Conclusion
Taking all the factors into account, all the grades of surface finish are important for the attractive appearance and functionality of stainless steel.
After reading this guide, you will understand all the types and techniques of surface finishes.
Now, if you have any doubts regarding your application’s surface finish, feel free to contact us.
Our experienced staff is always ready to assist you in selecting the right surface finish of stainless steel for your project.
