What are the different types of Stainless Steel?

Here at GF Laser, a question we are frequently asked is what are the different types of stainless steel?

There are three main grades that are used by laser cutting companies in the UK: 304, 316 and 310.

304 Stainless Steel: Representing half of the global steel production, Grade 304 stainless steel is known for its composition of 18% chromium and 8% nickel, contributing to its appealing appearance and robustness. However, its vulnerability lies in its reaction to saline environments, where exposure to salt water may lead to pitting or crevice corrosion. GF Laser maintains a stock of this steel grade in various thicknesses for diverse applications.

316 Stainless Steel: As the second most prevalent type of stainless steel, Grade 316 is distinguished by its 2-3% molybdenum content, enhancing its resistance to saline environments and making it more suitable for marine applications. It is also favoured for manufacturing surgical instruments due to its superior corrosion resistance. It is higher in cost than Grade 304, but GF Laser ensures availability in multiple thicknesses to meet all budgets.

310 Stainless Steel: Grade 310 stainless steel stands out for its flexibility and excellent welding characteristics, facilitating its use across a broad range of applications. Notably, 310 / 310S stainless steel (1.4845) excels in corrosion resistance at normal temperatures and is specifically engineered to perform under high temperatures. In such environments, it demonstrates unparalleled resistance to oxidizing, carburizing atmospheres, and other forms of hot corrosion, up to a maximum temperature of 1100ºC in dry air. This type of stainless steel isn’t widely used so although GF Laser do not stock it, we can obtain it, usually next day, from one of our steel stockholders.

For a stainless steel laser cutting quotation use our online quotation form today.

When answering the question what are the main types of stainless steel we also need to consider that there are a multiple number of finishes available to each grade of stainless, these are explained below. These specifications can vary between manufacturers and industries, so it’s important to refer to detailed standards or supplier documents for precise definitions when selecting or specifying this type of finish for a project. The team at GF Laser can help you decide on what is the best finish.

Category 1: Mill Finished Stainless Steel

There are 4 main finishes in Category 1:

2B Finish – Cold Rolled, Annealed, Pickled and Skin Passed Building on the 2D process. The 2B finish includes an additional skin passing step, refining the surface to a smoothness with average roughness between 0.1 and 0.5 micrometres. This makes it the preferred choice for mechanical polishing, offering a smoother and more uniform surface. At GF Laser if a finish isn’t specified we will generally supply 2B.

1D Finish – Hot Rolled, Annealed, and Pickled. This finish involves first hot rolling the steel through a mill, followed by annealing, a heat treatment that heats and then cools the steel slowly to lessen hardness and relieve internal stresses, making the steel more malleable. The final step, pickling, removes surface scales formed during hot rolling and annealing.

2D Finish – Cold Rolled, Annealed, and Pickled. The 2D finish, while similar to the 1D, involves cold rolling the steel for a finer process. Pickling remains a crucial step post-cold rolling to achieve the desired finish. Like the 1D, the 2D serves as a foundation for further finishing processes.

2R Finish – Cold Rolled, Bright Annealed, and Skin Passed Reserved primarily for applications requiring a reflective surface, such as household appliances and building materials. The 2R finish involves cold rolling and skin passing after bright annealing in an oxygen-free environment. This method prevents oxidation and scaling, resulting in a semi-reflective, easy-to-clean surface ideal for reflective polishing, including Bright or Mirror finishes.

Category 2: Mechanically Finished Stainless Steel

There are three main finishes in Category 2:

Grained Finishes: Often referred to as Dull Polished, this finish is achieved through the use of polishing belts made from abrasive aluminium oxide, which creates a unidirectional grain pattern on the surface of the sheet while also smoothing out minor imperfections.

There are various types of grained finishes available, such as 240G, 240S, and Satin Polished. The specific Ra measurement of the polished finish will depend on the initial use of a 2B finish. The grain specification chosen will result in subtle visual differences in the final product, making the choice of polish crucial, especially when matching to existing materials.

Dull polishing is a popular choice in industries such as catering, architecture, and pharmaceuticals due to its aesthetic appeal and functional benefits.

Reflective Finishes: Commonly referred to as Bright or Mirror Polish, this finish achieves its reflective quality through the use of mops and compounds. Like Dull polishing, there are varying degrees of reflective finishes, each conforming to specific Ra readings and levels of reflectivity. This method is gentler on the sheet’s natural finish and may not eliminate all surface defects.

The smooth mirror-like finish is perfect for applications requiring visual appeal and minimal contamination, such as trims, signage, marine, and pharmaceutical applications.

Circular Finishes: Achieved through the use of circular abrasive heads, Circle Polishing creates a distinctive, overlapping circular pattern on the surface. This method preserves much of the original surface, meaning pre-existing imperfections might remain. The pattern intensity can be customized to meet specific requirements and is frequently used in catering and architectural projects for its unique aesthetic quality.

So, as you can see, the answer to the question ‘what are the different types of stainless steel?’ isn’t an easy one! Fortunately the majority of our customers specify either 304 or 316 stainless steel in either mill or dull polished / mirror finish. If you do need more assistance though, please contact a member of the team today using our online contact form. Don’t forget we can also press brake (fold) stainless steel using one of our Amada press brakes.