which stainless steel grade

As a sub-contract machinist it is not uncommon that companies will come to us during the design phase of their product to check that their component is suitable for manufacture. Stainless Steel is often selected as a material due to its corrosion resistance, but there are hundreds of different grades. So how do you determine which is best for your application?

What is Stainless Steel?

A ‘Stainless’ Steel is an alloy of Iron which contains at least 10.5% Chromium. This Chromium content produces a thin oxide layer which is ‘passive’ to reaction in its environment. This helps protect the base metal from corrosion.

The 5 Key Categories For Stainless Steel

Austenitic Stainless Steels are the most common. Their structure incorporates Nickel, Manganese and Nitrogen. Ferritic Stainless Steels contain a small amount of carbon. Martensitic Stainless Steels have a higher carbon content then Ferritic Steels. Duplex Steels contain an even mix of both Ferritic and Austenitic material. Precipitation Hardened Steels add elements such as Copper and Aluminium to the steel.

Corrosion Considerations

It goes without saying that ‘Corrosion’ is a catch all phrase which includes degradation from a number of sources. The environment that a component needs to function in is key to its performance and key factors to consider include pressure, temperature and any corrosive sources such as chemical contact. Speaking in broad terms Austenitic Stainless Steels provide the most corrosion resistance due to their higher levels of Chromium content bad grades such as 304 and 316 are often selected for higher corrosive environments.

Heat Treatment

Generally Speaking Austenitic and Ferritic Stainless Steels will not be hardened when heat treated. Martensitic and Precipitation Hardened Stainless Steels can both be heat treated, Grades such as 440C AND 17-4PH can both be heat treated to increase their hardness.

Welding

The welding if Stainless Steels is very different then their carbon counterparts. The ‘most weldable’ grades are typically found in the austenitic group although ferritic stainless grades such as 430 and 439 are also readily weldable. Martensitic Stainless grades are only suitable for welding where they have lower amounts of carbon and PH Stainless is also a difficult one to weld without compromising its mechanical properties.

Sourcing

Last but certainly not least, it’s important to consider how easy any particular grade of Stainless Steel is to source. Many of the more popular grades such as 316 are in regular supply but that is not the case with every grade. Ease of procurement, delivery times and price should also be taken into consideration.

B&B Precision are sub-contract manufacturers with a wealth of experience in working with Stainless Steel of all grades. We have 4th Axis CNC machining and work to customer drawings. Send through your RFQ to see if we can help manufacture your Stainless Steel components.

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