Stainless steel finish

Take a close look at that piece of stainless steel. To the naked eye, your material may look smooth and consistent. But the truth all comes down to the finish, and the stainless steel polish.

How to polish stainless steel

Is the type of stainless steel finish I use important to my end product? It's perhaps one of the biggest debates in stainless steel, next to 304 vs. 316.

To get to that answer, let's first dig into the types of stainless steel finishes. There are two types of finishes: mill finishes and applied finishes.

Some products need only a standard finish. Others, however, require additional treatments to improve their appearance, environmental performance, or safety. This is where the polish comes in as a value-add to your stainless steel. There is also a question of whether the stainless finish can help protect stainless steel from rust.

Before you purchase your next stainless steel product, let's take a closer look at the different stainless steel finishes and polishes.

What is a 2b finish on stainless steel?

Let’s start with basic protection—which applies itself organically. All stainless steels are iron-based alloys containing at least 10.5% chromium. A reaction between that chromium and the oxygen in the atmosphere produces a chromium oxide film at the surface. This allows the film to immediately self-repair in the presence of oxygen in the event of any surface damage.

The next layer comes at the mill. Whether we are talking hot rolled or cold rolled, all stainless steel flat products are treated with a standard mill finish. Let’s review two of the more common mill finishes:

Cold rolling, heat treating, and pickling are used to achieve a desired result. A light rolling is applied at the end to give a smooth and reflective sheen. Considered the most widely used surface finish, 2B is the basis for most polished and brushed finishes. Such common stainless steel grades as 201304304L and 316L come in a standard 2B finish. 

Typical uses for a 2B finish include:

  • Cookware
  • Control panels
  • Kitchen equipment
  • Pharmaceutical equipment
  • Flatware
  • Pool liners

2D finish is achieved by cold rolling, heat treating, and pickling. Unlike 2B, it does not receive the light rolling. This results in a matte surface with low reflectivity.

It is perfect for industrial and engineering applications. Its appearance is distinct from that of 2B.

Typical uses for 2D finish include:

  • Automotive exhaust systems
  • Drawn parts or assemblies
  • Furnace parts
  • Rail car parts
  • Roofing and flashing products

What is a #1/Hot Rolled finish (HRA/P)

Commonly referred to as hot-rolled annealed and pickled or descaled. This is a dull, non-reflective finish. Generally used in industrial applications where smoothness of finish is not of particular importance. 

Typical uses for #1 HRA/P finish include:

  • Tanks
  • Heaters
  • Curtain Walls
  • Furnace Conveyors and Dampers
  • Incinerators
  • Tube Hangers
  • Pipe and tube products

What is a #4 finish on stainless steel?

Applied finishes may further enhance the surface appearance and environmental performance of your product. This requires physical alteration of the metal, most notably through the use of abrasive material that removes portions from the surface.

The higher the abrasive grit used, the finer and more reflective the look. One example of an applied finish is #4.

This finish is often found on restaurant and kitchen equipment, food processing machines, and dairy equipment. It can also be found in other places. This finish uses between 120 and 320 abrasive grit, depending on the application.

For comparison, applied finish #3 uses between 100-120. Grit affects surface roughness. This is usually measured in micro-inches or micro meters, and is referred to as "Ra" (roughness average). The higher the grit numbers, the finer the polishing lines and more reflective the finish.

Surface consistency is key to this type of finish. For example, some polishes can create a discoloration on the surface—think of a ‘checkerboard’ look to your metal.

What is a bright annealed (BA) finish?

A bright cold-rolled mirror like reflective finish produced by annealing in a vertical controlled oxygen free, hydrogen filled furnace.

Typical uses for BA finish include:

  • Auto/appliance trim
  • Truck parts
  • Commercial refrigeration cases
  • Truck trailer wrappers
  • Cookware
  • Surgical/dental instruments

What is a #8 finish?

With a #8 finish for stainless steel, you have directional and non-directional. With a directional #8 finish, you have more traditional product incorporating a series of finer passes. You may see some fine lines in the finish.

With a #8 non-directional finish you have finer material with no visible lines. This finish is generally available only in sheet, not coil.

Pit-Free Dairy Finish

In some cases, a material can have minor imperfections despite an applied finish. These imperfections are usually invisible to the naked eye. Most users won't be affected by this.

However, for food, dairy, or pharmaceutical applications, microscopic scratches or pits underneath the surface could trap bacteria or contaminants. This could create health hazards for the products being produced.

Enter Pit-Free Dairy. This type of stainless polish was developed as an alternative to standard 2B. The value of using this polish is that it provides consistency from piece to piece, clearing up imperfections. This intense polishing method removes all imperfections to create a true, smooth pit-free surface.

Enter Pit-Free Dairy. This type of stainless polish was developed as an alternative to standard 2B. The value of using this polish is that it provides consistency from piece to piece, clearing up imperfections. This intense polishing method removes all imperfections to create a true, smooth pit-free surface.

Pit free dairy

Check out more about what it means to create a pit-free finish from Guy Metals, part of the Ryerson Family of Companies. 

In the end, determining your polish and the specific needs of your application and properly conveying those to your producer could be the final step to ensuring your stainless steel is truly complete.


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