Stainless steel finishes are an important consideration when planning to improve the lifespan of equipment, as they can aid corrosion resistance and offer low maintenance requirements.
Although different standards offer their designation for each surface finish, manufacturers also offer in-house standards. However, you should prioritize the most widely accepted standards, like EN and ASTM, which guarantee the product’s surface behaves as expected.
Well, in this reading, we’ll explore the various kinds of stainless steel finishes and their suitability in various applications.
Let’s begin!
Learn about stainless steel with this detailed guide!
Stainless Steel Finishes EN & ASTM
There are over 150 unique grades of stainless steel available today, which include sheet, plate, bar, and tube. They are common in various industries, including architecture and automobiles, while stainless steel finishes play a crucial role in their applications.
The EN and ASTM equivalents provide a comprehensive overview of the possibilities of using these finishes.
The mill finishes, according to the EN designation, include 1D (hot rolled, heat treated, and pickled), 2B (cold rolled, heat treated, pickled, and skin passed), 2D (cold rolled, heated treated, pickled, and skin passed), 2H (hardened and cold worked for higher strength), 2R (cold rolled, bright annealed, and skin passed), and 2Q (cold rolled, hardened, and tempered).
On the other hand, polished and brushed finishes require the use of specific grades of grit or surface roughness, such as 1G-2G (ground), 1J-2J (brushed or dull polished), 1K-2K (satin polished), and 1P-2P (bright polished).
The patterned and colored finishes, according to the EN designation and ASTM equivalent, include 2F (No. 2D) (cold rolled, heat treated, and skin passed on roughened rolls), 1M (one side is flat), 2M (one side is flat), and 2W (both sides with corrugated texture).
Additionally, it features 2L (colors as agreed upon) and 1S-2S (surface coating), typically coated with tin, aluminum, or titanium. These finishes offer a wide range of benefits which include ensuring durability, corrosion resistance, a reflective surface, smoothness, and specific grain patterns. Let’s go deeper to further discuss them.
Types of Stainless Steel Finishes
The various types of steel finishes include mill finishes, brushed and polished finishes, and bright annealed and temper rolled finishes.
Mill Finishes
Mill finishes are a kind of stainless steel finish suitable for smooth surfaces, as they produce matte finishes. They are often used due to their durability
Hot or cold stainless steel requires this finishing process to meet the application output. The common types of stainless steel mill finishes include
1D Stainless Steel Finish:
The 1D stainless steel finish can be achieved through hot rolling, annealing, and pickling. The steel undergoes annealing, a heat treatment that removes internal stress and reduces hardness, making it more ductile and workable.
The surface is then cleaned with acid to eliminate the scales that formed during the previous processes. The resulting surface is slightly coarse with low reflectivity and a roughness (Ra) between 4 and 7 micrometers.
1D stainless steel is sometimes used as a starting point for polished finishes, but its non-decorative applications include unexposed support systems, structural applications, air heaters, furnace conveyors, heat exchangers, and oil burner parts.
The surface finish is suitable for various applications, including furnace conveyors, heat exchangers, and oil burner parts.
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2D Surface Finish:
The 2D surface finish of cold-rolled stainless steel is refined and enhanced through annealing and cold-rolling processes. This process removes stress and reduces hardness, resulting in a low reflective matte appearance.
The surface finish serves as a foundation for polished finishes, catering to a wide range of industrial and engineering requirements.
Common applications include railway parts, automotive exhaust systems, builders’ hardware, chemical equipment, electric range parts, stone anchors, roof drainage systems, and petrochemical equipment. The process ensures a low reflective matte appearance and improved performance.
2B Finished:
2B Cold-rolled stainless steel is used in various applications, such as baking equipment, refrigeration, food processing, tanks, vessels, vacuum drum dryers, solar collector panels, and pharmaceutical equipment. The 2B finish is a smooth, slightly to moderately reflective surface with excellent flatness control.
This finish bears a resemblance to 2D production, albeit with an additional step of rolling it once more using highly polished bright rolls. The average roughness obtained is between 0.1 and 0.5 micrometers, making it suitable for architecture where uniformity of finish is not a requirement.
2R Finish:
The 2R finish, also known as BA stainless steel, is a surface finish for stainless steel used in domestic and commercial applications. It features a cold-rolled, bright annealed process, which protects the steel from oxidation and scaling. This process ensures a smooth, easy-to-clean surface with a typical Ra between 0.05 and 0.1 micrometers.
The 2R finish is commonly used in applications where reflection is important but precision is not, such as inner parts of washing machines, commercial refrigerators, food processing equipment, builders’ hardware, surgical instruments, highway truck trailers, and road mirrors.
2H Finish:
The 2H stainless steel surface finish is a unique blend of cold-rolled and work-hardened steel. This process involves cold-working the metal to enhance its strength, followed by temper-rolling polished rolls. The result is a smooth, reflective finish with six levels of strength based on yield strength, tensile strength, and elongation.
Manufacturers determine the surface roughness based on the temper rolling process. Common applications include automotive, machinery, press plates, surgical instruments, implants, and stamping parts.
2Q Finish
The 2Q stainless steel finish, similar to the 2H finish, is cold rolled and hardened, with the surface being smooth and free of scale. Manufacturers specifically use it on martensitic steels that respond to these treatments. The surface roughness is defined by manufacturers, and its applications are similar to the 2H finish, including automotive, machines, and surgical instruments
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Polished & Brushed Stainless Steel Finishes
When selecting a stainless steel surface for an application, it is essential to consider the desired outcome and minimize the number of additional processes. Mechanically polishing and brushing the surface can achieve standard finishes, using abrasive materials to cut the steel to a desirable degree.
The resulting surface finish depends on factors such as the original surface, type and texture of polishing belts and brushes, and the nature of the polishing process. Mechanical processes achieve brushed and polished finishes, which are more abrasive than mill finishes.
The surface finishing outcome depends on the steel’s starting point and the type of belts, brushes, and polishing process selected.
Grinding is a common brushed and polished finishing technique, producing a refined surface. Other variables affecting the end surface include the amount of time the metal is in contact with brushes and the pressure.
This type of stainless steel finish produces a highly reflective and polished finish, making it an ideal choice for aesthetic and ornamental applications. Below are the various types of mechanically polished and brushed stainless steel finishes:
1G–2G Finish:
The surface of 1G–2G Stainless Steel Finish is achieved through grinding, with the 1G referring to a hot-rolled starting point and the 2G referring to a cold-rolled one. This process produces a coarse, unidirectional surface with low reflectivity, with surface roughness varying between manufacturers and customers.
Common applications include brewery equipment, food processing equipment, kitchen equipment, scientific apparatus, and indoor architectural applications.
1J–2J Finish:
The 1J–2J stainless steel finish starts with the same starting points as previous finishes but now uses polishing belts or brushes to achieve a more refined surface. The surface roughness ranges from 0.2 to 1.0 micrometers, with most manufacturers preferring 0.4 to 0.6 micrometers.
Architectural wall panels, beverage equipment, highway tank trailers, furniture, elevator doors, interiors, sinks, and sterilizers frequently use the 1J–2J stainless steel finish. The surface roughness can be specified by the manufacturer.
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1K–2K Finish:
The 1K–2K finish is a highly corrosion-resistant surface made from hot- or cold-rolled steel, with an average roughness of 0.5 micrometers or lower.
This finish is suitable for various applications, including marine and external architectural applications, coastal environments, and ornamental applications. The surface is smooth and reflective, with some manufacturers reaching as low as 0.06 micrometers.
1P–2P Finish:
The 1P–2P stainless steel finish is a non-directional, ultra-smooth, and highly reflective surface finish with a high degree of image clarity in reflection. It is considered the best surface for corrosion resistance and is used in various applications such as column covers, ornamental trim, external wall panels, mirrors, reflectors, and signage.
The final polishing process involves soft cloth mops and special polishing compounds, resulting in a bright polished finish. The surface finish is suitable for a wide range of applications.
Patterned Finishes
We can produce stainless steel with patterned finishes using patterned rolls, creating a stiffened sheet that enables thinner gauge cladding. Applying the pattern on one or both sides can result in 2-sided patterned stainless steels, thereby achieving cost savings and weight reduction.
The 2F finish is a low-reflective stainless steel finish with a uniform matte surface on both sides. Common applications of this finish include automotive exhaust systems, builders’ hardware, chemical equipment, and roofing. The 1M–2M stainless steel finish is a 1-sided patterned stainless steel with one flat side and different textures.
The design depends on the specific application and is used to avoid accidental knocks and scratches. Popular applications include building entrances, elevator cages, and airport terminals.
The 2W stainless steel finish is a 2-sided patterned stainless steel with a corrugated texture on both sides. We agree on the pattern design, which enhances strength and adds aesthetic value. The applications are similar to the previous finishes, except that both sides may be visible. The surface roughness is defined and agreed upon upon request.
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Coloured Finish
Stainless steel applications often utilize colored finishes, which utilize the corrosion-resistant properties of the inert chromium layer at the surface. These finishes can be easily colored through chemical processes and hardened by electrolytic processes, resulting in electrolytically colored finishes.
These finishes can also be patterned if necessary. The 2L stainless steel finish, a designation for all colored finishes, is primarily used for decorative or ornamental purposes and can also be used to match with other materials in complex designs.
Conclusion
Stainless steel finishes enhance the visual appeal of the metal but also impact its functionality, durability, and suitability for specific applications. From reflective mirror finishes to brushed and matte textures, each finish offers different benefits in terms of aesthetics, corrosion resistance, and ease of cleaning.
Knowing the right finish is essential for different equipment and environments, such as architecture, food processing, medical equipment, and industrial uses. Understanding the characteristics of each finish ensures the stainless steel meets both performance and design requirements.
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FAQs on Stainless Steel Finishes
What are stainless steel finishes?
They are surface treatments or textures applied to stainless steel to alter its appearance, texture, reflectivity, and corrosion resistance.
What are common types of stainless steel finishes?
Common finishes include No. 1 (hot rolled), No. 2B (smooth, dull), No. 4 (brushed), and No. 8 (mirror or polished).
Which finish is best for kitchens and appliances?
No. 4 brushed finish is popular in kitchens and appliances due to its modern look and ability to hide fingerprints and scratches.
What is a mirror finish?
Also known as No. 8, it is a highly reflective, polished finish used for decorative or high-end applications.
Do stainless steel finishes affect corrosion resistance?
Yes. Smoother finishes like 2B and mirror polish are more resistant to corrosion since they have fewer surface crevices for contaminants.
Can finishes be applied after fabrication?
Yes, finishes can be applied post-fabrication through polishing, brushing, bead blasting, or other mechanical processes.