The surface finish of stainless steel affects much more than just its aesthetic — performance, reliability, and other factors can be greatly impacted.
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No matter the application or end-use of the stainless steel, its surface finish should be carefully chosen to best meet the requirements at hand. That's because, in addition to providing the desired visual appeal, the choice of finish affects corrosion resistance, characteristics such as electrical properties, impacts weldability, manufacturing operations, and contributes to various economic considerations.
Some applications, such as superconductor components or flexible metal hoses, demand stainless steel with a specific finish for the end-use product to perform as designed.
It's also important to note that not all suppliers use the same terminology to refer to the same finish. Keep reading to learn the subtle differences between each finish to understand better how suppliers may differ.
Surface finish is the visual appearance of the metal and is created through various processing methods, including rolling, polishing, and blasting. These finishes range from dull to bright and include special textures that may be mechanically applied for highly specialized applications.
Several factors can affect surface finish, including the production route, material thickness, the surface finish of the rolls, cleanliness, and mechanical abrading.
Most melt mills can produce all sheet and strip finishes. While some finishes (BA and polished) require specialized lines, most mills have these or a third-party processing partner. However, melt mills won't always be able to meet each customer's unique Ra (surface roughness) requirements, and a precision re-roller may be needed.
Surface finishes are commonly identified by standard industry designations based on process routing (not appearance) and are different for sheet (greater than 24” wide) and strip (less than 24” wide). However, as previously mentioned, some suppliers use proprietary designations or different industry standards, so it’s best to double-check that you’re on the same page.
Ulbrich's surface finish designations are based on ASTM A480 specifications. Below is an overview of the types of finishes available on our sheet products.
Whether hot or cold rolled, these finishes are the basic supply condition for all stainless-steel sheet products. They are universally used for many applications and serve as the starting point for mechanical polishing and other finishing processes. To maximize corrosion resistance, most are cleaned with acid (pickled) to remove scale that builds up during hot rolling and annealing (a bright annealed finish being the exception!)
A No. 1 Finish is produced via hot rolling, then annealing and pickling the material in acid. This results in a dull finish and is typically used when a smooth decorative finish isn’t important, for example, in elevated temperature applications.
A No. 2D Finish is produced via cold rolling, then annealing and pickling the material in acid. The finish is smooth, non-reflective, and dull. It is ideal for deep drawing applications and is found in auto exhaust components, hardware, and chemical equipment.
A No. 2B Finish is cold rolled, annealed, and pickled, followed by a light temper pass using polished rolls. The finish is smooth, somewhat reflective, and bright. It’s a general-purpose cold-rolled finish used in cookware, small tanks, and pharmaceutical equipment.
A Bright Annealed Finish is cold rolled, then annealed in a controlled, protective atmosphere to prevent scale formation during annealing. This finish is not pickled in acid because a thin oxide film is formed during annealing, eliminating the need for pickling. It is used in trim appliances, surgical instruments, and cookware.
These finishes involve using abrasive materials that effectively cut the steel's surface to some degree.
No. 3 and No. 4 finishes are produced by mechanically polishing a No. 2B finish substrate. These finishes have uniform appearances that are produced by an emery cloth belt used for polishing. Each finish has a corresponding grit necessary to create its surface texture.
These finishes are among the most used in stainless steel. Applications featuring No. 3 finishes include architectural and food processing components. Applications featuring No. 4 finishes include architectural wall panels, elevators, sinks, and restaurant equipment.
A No. 6 finish is created by Tampico brushing a No. 4 finish. It’s dull, silver-white, and less reflective than a No. 4 finish. This finish was once commonly found on stainless steel architectural components up to the 1980s but is much less used today.
A No. 7 finish is produced by buffing a finely ground surface. The finish is high luster with grit lines still visible on the material. The result is highly reflective, almost mirror-like. Some common applications for No. 7 finishes include column covers, ornament trim, and wall panels.
This is produced by polishing with successively higher grit abrasives and then buffing for a mirror finish. By ASTM standards, they are the most reflective of all finishes.
Because they are so reflective, No. 8 finishes have a lot of notable everyday applications, including press plates, signs, and wall panels. Most notably, Chicago’s “Bean” is stainless steel with a #8 finish.
Custom metal surface finishes allow for specific characteristics to be unlocked that are not available if a standard finish is specified. Engineers for advanced and emerging applications specify the surface roughness in Ra or Rz (see below) that they need to meet their objectives.
For custom surface finishes beyond those mentioned here, contact us to connect with a metallurgical engineer who can assist.
A TR finish is produced when an annealed surface is cold rolled to obtain mechanical properties. The appearance varies based on the alloy and the amount of cold work. Quarter hard, half hard, and full hard are common examples of temper-rolled finishes. This finish is used all the time and is one of the largest categories of stainless steel that we sell at Ulbrich.
An architectural finish can be achieved through special finishes at the temper mill, the final reduction stand, special pickle processes, or a combination. These are typically agreed upon between buyer and producer.
Abel Black™ stainless steel is made using a proprietary coloring method that preserves its metallic texture (unlike painting or plating). Electricity and chemicals are used to create an oxide film that causes light inference, making the stainless-steel surface appear black. Since the oxide film is integrated with the base metal, it will not peel off and delivers higher durability and weather resistance than untreated stainless steel.
XL Blend "S" is a breakthrough stainless steel finish. It can repair surface damage, creating a clean, smooth, and uniform exterior. The finer grain structure makes it less reflective and less receptive to foreign substances, resulting in a surface that is easier to clean and maintain. Common applications include escalators, transportation, and food service appliances.
Abel Black and XL Blend S are both available from Diversified UIbrich!
Any discussion of surface finish would be incomplete without mentioning surface roughness. Surface roughness is a measure of the texture of a manufactured surface. RA or Average roughness is most commonly used in North America. It is the average of the peaks and valleys of a surface over a set sampling length. Values are typically given in microinches or micrometers.
Rz, or mean roughness depth, is most commonly used in Europe and is the average of the highest peak to the lowest valley over 5 sampling lengths.
Surface roughness can have a crucial impact on the durability and performance of the material and must also be closely considered and controlled for.
Still unsure which finish is right for your application? Contact us and speak with someone from our metallurgy or product development team. We also offer custom finishes beyond those mentioned here to accommodate advanced and emerging applications, such as superconductors.
Stainless steel finishes offer a range of benefits. You can think about finishing as a fabrication process applied to enhance the metal’s surface character. Whether you need durability, corrosion resistance, a reflective surface, smoothness, or a specific grain pattern, any are available and desirable depending on the ultimate end use.
Now, there are over 150 unique grades of stainless steel. Stainless steel sheet, stainless steel plate, stainless steel bar, and stainless steel tube all find their way into an impressive range of industries. In fact, from the architecture industry to the automotive industry, stainless steel finishes help to achieve different visual and mechanical effects that will meet wide ranging needs.
Are you interested in learning more about stainless steel sheets patterned? Contact us today to secure an expert consultation!
Kloeckner Metals is a full-line stainless steel supplier and service center. Get our stainless steel spec sheet and check what Kloeckner Metals routinely stocks.
Stainless finishes fall into three main categories: mill finishes, brushed and polished finishes, and bright annealed and temper rolled finishes.
Mill finishes produce matte finishes that are most suitable for industrial uses and when a smooth surface is not required. Usually, mill finishes are selected for end uses where durability remains the highest priority.
Brushed and polished finishes are mechanically achieved. These finishes are considered more abrasive than mill finishes. The surface finishing outcome depends on the steel’s starting point—for instance, how rough or uniform the surface is—and which belts, brushes, and polishing process is selected. Grinding is one of the more common brushed and polished finishing techniques and will produce a more refined surface.
Other variables that will affect the end surface include the amount of time the metal is in contact with the brushers and the amount of pressure.
This type of stainless steel finish produces a highly reflective and polished finish. It is the ideal choice for aesthetic and ornamental applications.
Bright annealed finishes are produced by heat treating the stainless steel. The annealing processes is closely monitored in a controlled atmosphere or with vacuum protection. Once the stainless is heated to melting point, it is rapidly cooled. The end goal is a more corrosion resistant product that maintains good weldability and smoothness. As the name suggest, this finishing process leads to a brighter surface quality.
One of the main advantages of this kind of stainless steel finishing process is its protective layer which improves cleanliness, as it prevents oil and oxide adhesion.
There are three very popular mill finishes: No. 1 stainless steel finish, 2B stainless steel finish, and 2D stainless steel finish.
No. 1 mill finishes are achieved by hot rolling the stainless steel to a desired thickness. They tend to look dark and varied, and demonstrate the roughest, least uniform surface character of all of the stainless steel finishes. They do not have a reflective nature. Typically, No. 1 mill finishes are selected when aesthetic appeal is the lowest priority. Often, No. 1 finishes are followed up with a pickling process which will strengthen the corrosion resistance. One of the main disadvantages for this type of finish is that it does not have a reflective surface and will only be useful for applications where look, feel, and brightness are not required.
Some of these applications include:
2B stainless steel finish is perhaps the most popular stainless steel finish. This cold roll finish produces a clean matte finish. It’s mainly non-reflective and smooth with excellent evenness. The stainless steel is annealed and pickled following the cold rolling process. After this, 2B stainless steel passes through “bright rolls.” This extra step gives 2B its characteristically smooth, flat surface.
Examples of applications with 2B stainless steel finish include:
2D stainless finish relies on a similar processing technique to 2B stainless steel finishes. Though it is also cold rolled, annealed and pickled, 2D stainless steel finishes maintain a duller, matte finishing quality.
2D stainless steel finishes show up in:
You might wonder, “What is annealed metal?” or, “How does annealing effect stainless steel?” and these are great questions! Both 2D and 2B stainless steel finishes are annealed in order to counter some of the effects caused by the cold rolling process. In short, annealing removes stress and reduces hardness. Pickling is then needed to level out the finishing character by removing any impurities caused by the annealing process.
There are three main types of brushed and polished finishes: #3, #4, and #8 (Mirror Finish).
#3 finish is a brushed finish achieved by rough grinding. This finishing process typically yields a surface finish that is coarse, unidirectional, and low to non-reflective. The material grade as well as the type and quality of grinding belt, will impact the amount of surface roughness.
This stainless steel finish is often used for:
#4 finish produces a more refined surface. It is processed with polishing belts and brushes that will still result in a mildly reflective and one-directional surface quality. The ultimate roughness is determined by the brush grade, and quality of the polishing belt.
#4 finish is known to have a distinct look characterized by a muted color and very fine lines. It suits many decorative needs. However, only those that do not require reflectiveness. One of the main drawbacks for this kind of stainless steel finish is its reduced corrosion resistance.
As a result, it’s always recommended to confirm with your metal supplier and metal fabricator to ensure that the stainless finish meets your requirements.
This type of finish is best suited for:
#8 stainless finish is also commonly referred to as “mirror finish” because of its highly reflective nature. So much so that the stainless steel mimics the appearance of a mirror. This finish requires additional buffing, usually somewhere between five and ten minutes. This extra polishing time results in nearly invisible line quality. Any imperfections are removed.
Here are some of the popular applications for this finishing process:
Two of the most common stainless steel grades are 304 and 316. They can undergo various finishing processes, including #2B, #2D, #3, #4, and bright annealed.
Kloeckner Metals routinely stocks the most popular stainless steel grades in a range of stainless steel formats with the highest quality finishes. You can click to learn about different stainless steel grades and the different types of stainless steels or reach our sales team today to discuss your project’s requirements.
Kloeckner Metals is a full-line stainless steel supplier and service center. Kloeckner Metals offers a national footprint with the latest fabrication and processing technologies and most innovative customer service solutions.
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