The appearance of stainless steel comes down to how it was finished. Some stainless steels look smooth and consistent, while others look grainy and rough — all of which are outcomes of the finishing processes. Whether you are looking for durability, corrosion resistance, or low cost, there is a distinct finish for your requirements.
This article will define a surface finish, describe the finishing process, and discuss the different types of stainless steel finishes.
What Is a Surface Finish?
Surface finishing alters the outermost layer of a metal by adding, removing, or reshaping. This essential technique aims to protect the metal while improving its appearance.
The surface finish chosen is critical where fabrication processes will be used. For example, rough surface finishes are appropriate when the steel is ground before painting and gluing, whereas smooth surface finishes are preferred when the steel is blended. On the other hand, a visually appealing surface finish is necessary for projects where design is a priority.
How Does the Stainless Steel Finishing Process Work?
The primary finishing method is to “cold roll” the stainless steel through special rolls or dies. Cold rolling usually results in smoother, less pitted surfaces. It is then softened and de-scaled in an acid solution before the steel is given a final pass on polished rolls to improve its smoothness.
Different finishes suit various requirements. Here is a closer look at the commonly used finishes for most stainless steels and their applications.
What Are the Different Finish Types?
The various types of finishes are graded on a scale of 0 to 10.
This finish is also known as Hot Rolled Annealed (HRA) steel. The plate is hot rolled to the required thickness before annealing, which results in a rough, scaled-black finish. This process does not produce a completely corrosion-resistant film on the stainless steel, and it is not suitable for general use except in specific high-temperature heat-resistant applications.
The plate is hot rolled, annealed, pickled, and coated in this finish type. The process produces a dull, slightly rough surface ideal for industrial applications involving various plate thicknesses. Several applications of the No. 1 finish include the following:
- Air heaters
- Annealing boxes
- Carburizing boxes
- Firebox sheets
- Furnace conveyors and linings
The No. 2 finish can be classified into multiple subcategories:
– No. 2D
This finish type is the No. 1 finish after being cold rolled, annealed, pickled, and coated. It produces a more uniform matte finish than No. 1. It is also used in the following applications:
- Chemical equipment
- Electric range parts
- Furnace parts
- Railcar parts
– No. 2B
This second subcategory is a No. 2D finish with a light skin pass cold rolling operation between the rolls. However, the No. 2B finish has higher reflectivity and brightness. It is also the most commonly produced and requested finish on sheet materials. It is typically used in applications such as the following:
- Dyehouse equipment
- Pharmaceutical equipment
- Plumbing fixtures
– No. 2BA
This type is referred to as a Bright Annealed (BA) finish. It is created by cold rolling a No. 1 finish on the steel surface with highly polished rolls. This aids in smoothing and brightening the surface, and its applications include the following:
- Architectural components
- Commercial refrigerators
- Fishing equipment
- Surgical instruments
This finish type is produced with an abrasive of 80-100 grit. It is also an excellent intermediate or starting surface finish for use when the steel will require additional polishing processes to a more refined finish after succeeding fabrication. Among its applications are the following:
- Brewery equipment
- Kitchen equipment
- Food processing equipment
- Scientific apparatus
The remaining finishes are defined by the eventual outcome of the finish rather than by a structured methodology:
- 4: Similar to No. 3 but with slightly higher polish and reflectivity; used in applications such as appliances, beverage equipment, elevator doors and interiors, and water fountains.
- 5: Satin; most widely used in coastal architectural elements where a reflective or bright finish is not suitable
- 6: Satin (Scotch-BriteTM)
- 7: Reflective but not clear; used in architectural and decorative applications
- 8: Mirrored; used in column covers, mirrors, ornamental trim, press plates, wall panels, and signage
- 9: Ultra-mirrored with a bead-blasted surface
- 10: Electropolished and heat-colored
High-Quality Finishing Services at AAA Metals
Finishes should always be specified and defined using industry-standard designations. At AAA Metals, we can make your project a reality!
We specialize in stainless steel polishing for consumables, discs, forgings, pipes and tubing, rings, and pumps in all industries. We have been a frontrunner in stainless steel polishing for over three decades, with complete in-house capabilities for belt sanding, grinding, face, edge, and OD polishing. Moreover, our advanced tools include multi-head machines and belt sanders with ceramic, zirconia, and nylon-impregnated polishing belts.
Contact us directly for more information on our high-quality stainless steel finishing services or other capabilities, or you can request a quote today!