The choice of a stainless steel finish is crucial for its long lifespan, corrosion resistance, and low maintenance needs. Different standards offer their designations for each surface finish, and some manufacturers even create in-house standards.
To simplify the process, it is recommended to focus on the most recognized standards around the world, such as EN and ASTM standards, which are common and ensure the surface of the product behaves as expected. Well, in this reading, we’ll explore the various kinds of stainless steel finishes and their suitability in various applications.
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Stainless Steel Finishes EN & ASTM
Stainless steel finishes are a crucial aspect of the fabrication process, enhancing the metal’s surface character. There are over 150 unique grades of stainless steel, including sheet, plate, bar, and tube, which are used in various industries, such as architecture and automotive. The EN and ASTM equivalents provide a comprehensive overview of the possibilities of using these finishes.
Mill finishes, according to the EN designation, include 1D (hot rolled, heat treated, pickled), 2B (cold rolled, heat treated, pickled, and skin passed), 2D (cold rolled, heat treated, pickled, and skin passed), 2H (work hardened, cold worked for higher strength), 2R (cold rolled, bright annealed, and skin passed), and 2Q (cold rolled, hardened, and tempered).
Polished and brushed finishes, on the other hand, involve the use of a specific grade 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).
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), 2W (both sides with corrugated texture), 2L (colors upon agreement), and 1S-2S (surface coating) (generally coated with tin, aluminium, or titanium). These finishes offer a wide range of benefits, ensuring durability, corrosion resistance, a reflective surface, smoothness, and specific grain patterns.
Related: What is Stainless Steel? Its Properties, Types & How it’s Made
Types of Stainless Steel Finishes
The various types of steel finishes are categorize into mill finishes, brushed and polished finishes and bright annealed and temper rolled finishes.
Mill Finishes
Mill finishes are suitable for industrial uses with a smooth surface, often chosen for durability. They produce matte finishes, making them suitable for end uses. Stainless steels, whether cold or hot rolled, require additional finishing processes to meet specific applications, making mill finishes the basic supply condition for these steels. The common types of stainless steel mill finishes include:
1D Stainless Steel Finish
The 1D stainless steel finish is 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 remove scales, which form during the previous processes. The resulting surface is slightly coarse with low reflectivity and a roughness (Ra) between 4-7 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.
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 matt appearance. The surface finish can be used as a starting point for polished finishes and is suitable for various industrial and engineering needs.
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 matt appearance and improved performance.
2B Finish
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 good flatness control.
This finish is similar to producing 2D but with an extra step of rolling it one final time with 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 0.05-0.1 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 on polished rolls. The result is a smooth, reflective finish with six levels of strength based on yield strength, tensile strength, and elongation.
The surface roughness is determined by manufacturers and depends 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. It is specifically used 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
Related: Stainless Steel Welding: Methods, Challenges and Best Practices
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. Brushed and polished finishes are mechanically achieved and are considered more abrasive than mill finishes. The surface finishing outcome depends on the steel’s starting point, 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 brushers 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.
The 1J – 2J stainless steel finish is commonly used in architectural wall panels, beverage equipment, highway tank trailers, furniture, elevator doors and interiors, sinks, and sterilizers. The surface roughness can be specified by the manufacturer.
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, achieving a bright polished finish. The surface finish is suitable for a wide range of applications.
Patterned Finishes
Using patterned rolls, stainless steel can be produced with patterned finishes, resulting in a stiffened sheet that allows for thinner gauge cladding. This subsequent cost savings and weight reduction can be achieved by applying the pattern on one side or both sides, achieving 2-sided patterned stainless steels.
The 2F finish is a low-reflective stainless steel finish with a uniform matt surface on both sides. It is commonly used in automotive exhaust systems, builders’ hardware, chemical equipment, and roofing. The 1M – 2M stainless steel finish is a 1-sided patterned stainless steel with flat one 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, lift cages, and airport terminals.
The 2W stainless steel finish is a 2-sided patterned stainless steel with a corrugated texture on both sides. The pattern design is agreed upon and increases strength while offering aesthetic value. The applications are similar to the previous finishes, but with the difference that both sides may be visible. The surface roughness is defined and agreed upon upon request.
Related: What is Sheet Metal? its Types, Sizes & Forming Processes
Coloured Finish
Stainless steel applications often utilize coloured finishes, which utilize the corrosion-resistant properties of the inert chromium layer at the surface. These finishes can be easily coloured through chemical processes and hardened by electrolytic processes, resulting in electrolytically coloured finishes.
These finishes can also be patterned if necessary. The 2L stainless steel finish, a designation for all coloured finishes, is primarily used for decorative or ornamental purposes and can also be used to match with other materials in complex designs.
