One aspect of procuring and fabricating stainless steel sheet that often gets overlooked is what finish to specify. Having the proper finish on your stainless steel product will go a long way to ensuring the long-term effectiveness and durability of a product. Spec the wrong finish, and it could render a finished product worthless.
With all the versatility and technical advances available in modern stainless steel products, it should come as no surprise that there are a wide range of surface finishes available. Every product designer and manufacturer should have a basic understanding of the various finishes and how to tell them apart. Factors such as the intended use of the finished product, the harshness of the environment and the life cycle of the parts help determine which finish to use.
Today’s subject will compare the various types of stainless steel finishes and how to determine the right one for any given job.
The advantages of stainless steel sheet
As one of the most versatile and durable metals available on the market, there are a lot of great reasons to select stainless steel sheet. Compared with other materials, it’s easy to see why stainless steel is often the most cost effective option available without sacrificing performance.
First, stainless steel is widely recognized for its tremendous strength. All steels are renowned for their durability and toughness, and stainless steel is no exception. A key feature is that stainless steel will retain its resilience even at extremes of temperature.
Stainless steel got its name due to its premium corrosion resistance. Thanks to the addition of chromium, stainless steel has an inherent defense against rust, water stains and other forms of corrosion. The added chromium leads to the formation of a passive film that self-heals in the presence of oxygen. This natural resistance can be boosted even further when the chromium content exceeds 11%, or other alloying elements are added, such as nickel and molybdenum.
Another positive attribute of stainless steel is the fact it is extremely hygienic. It’s a great option for health care facilities, kitchens and labs where cleanliness is a high priority because it helps avoid the growth of bacteria and other pathogens. The surface is also easy to clean and maintain. At the same time, stainless steel is also highly aesthetic, thanks to its brilliant sheen, something that can be further accentuated with the right finish.
As already mentioned, stainless steel is extremely tough, meaning that it’s highly durable. Its ability to withstand tremendous load and pressure, as well as its high resistance to corrosion, results in products with a long lifecycle. Moreover, when stainless steel products reach the end of their service, they are easy to recycle. Most stainless steel on the market today comes from recycled metal.
What are the most popular finishes for stainless steel?
With all those advantages, it’s no wonder that stainless steel is such a valuable material. Choosing the right finish can be a confusing process; not only are there many options available, but the numbering system used requires some explanation.
Standard mill finishes are applied after the steel has been flat rolled. Once the steel has been rolled to the desired size and thickness, it will be annealed, with any surface oxidation removed by pickling. This process results in a passivation layer that can have a finish applied to achieve the desired appearance.
The standard finishes that are available for stainless steel are categorized by a numbering system. However, it should be noted that different alloys and thicknesses can result in different appearances, even with the same finish. It shouldn’t be assumed that two different alloys will look the same.
The most basic finish is known as #0; the product simply hot rolled and annealed. It is not appropriate for most products. The disadvantages include a black finish on the surface, without any pickling or passivating processes. It will even hinder the corrosion resistance of the metal. It is generally reserved for certain high temperature heat resisting applications.
A #1 finish is the product of annealed material that undergoes the hot rolling as well as a pickling process. It may also be designated HRAP (Hot Rolled Annealed & Pickled). The final appearance will be dull, with a generally rough surface. This finish will be mostly used with industrial applications.
There are several common finishes in the #2 class. First of note is #2D, which involves the sheet or plate being cold rolled, annealed, then pickled and passivated. It results in a matte finish that will appear uniformly dull. It is suitable for industrial parts and is especially common in drawing applications, thanks to the fact that the surface will retain lubricants critical to the drawing process.
#2B, also cold rolled, annealed, pickled and “pinch-passed.” It is a light finish that is semi-reflective. It is probably the most popular finish for stainless steel sheet and is frequently used with deep drawing. The final cold rolling process uses polished rolls to give it a more reflective appearance.
#2BA is a bright annealed, cold rolled finish. It offers a smooth, reflective surface. The annealing process is performed in a controlled atmosphere to reduce oxidation and scaling during annealing. It also has a final rolling pass using polished rolls for a more reflective finish.
While the above finishes are all considered mill finishes (generally hot or cold rolled & annealed), the remaining finishes are considered mechanical in nature. They employ abrasive or polishing equipment to impart the desired finish to flat rolled stainless stock. #3 finish is a grinding finish using abrasive media in the 80- to 100-grit range. It lends itself to an intermediate brushed finish and is frequently used when additional finishing may be required after fabrication.
The #4 finish is of at least 150 grit and offers a uniform brush direction without being highly reflective. It is considered a good all-around finish and is frequently found on parts that will used in a service environment. The #6 finish is cloth buffed, resulting in a non-directional finish and a variable reflection amount. Finally, a #8 finish involves extremely fine buffing and is associated with a true mirror finish.
When working with stainless steel sheet, it’s a good idea to partner with an experienced material supplier like Clinton Aluminum. Contact a friendly and professional customer service representative at Clinton today to learn more.