What Is Austenitic Stainless Steel?

Stainless steel is commonly found in many industries and environments; from the workstations and utensils of industrial kitchens to medical devices and automotive applications.

But like all metal alloys, there are multiple types and grades of stainless steel. Stainless steel can be graded, above the series of alloys e.g. 300, 400, etc., by its chemical composition. These overarching groups are known as Austenitic, Martensitic and Ferritic. In this article, we’ll explore Austenitic Stainless Steel in more detail.

What is the difference between Austenitic and Martensitic Stainless Steel?

Austenitic Stainless Steel

Because of the alloying elements, Austenitic stainless steels are Face-Centered-Cubic in atom structure, meaning they are very tough, with plenty of ductility to be bent and formed. Austenitic stainless steels are high in chromium and nickel.

Martensitic Stainless Steel

With a Body-Centered-Cubic atomic structure, Martensitic stainless steels are much harder, with much less malleability. This makes them ideal for utensils such as knives and scrapers, where a sharp edge is required.

Why use Austenitic Stainless Steel?

Workability

Thanks to its crystal structure, Austenitic stainless steel is relatively malleable and ductile. This means it is suited well to make production manufacturing techniques, such as bending, shearing, stamping and punching.

Cost

Whilst stainless steel is rather more expensive than mild steel, the ease of working, coupled with the fact it does not need to be protected from corrosion, means it can be cheaper than some alternatives.

To find out how much the stainless steel will be for your project, check out the grades we stock here.

Strength

316 grade stainless steel has a tensile strength of around 550 MPa, this is approximately equivalent to that of S355 grade mild steel, a medium strength steel used in structural applications.

This means stainless steel can be used for structures and other high stress components in place of steel, but with better corrosion resistance.

What Grades of Stainless Steel are Austenitic?

As with most modern materials, there are many different grades of stainless steel, termed series’, these range from 200 up to 400, with many sub-grades in-between such as 202, 304, 430, etc.

The grades that are Austenitic are those in the 200 and 300 series, this includes the most commonly used 304, and 316 grades.

Applications of Austenitic Stainless Steel

Thanks to its great workability, excellent corrosion resistance and ease of manufacture, Austenitic stainless steel is found in all walks of life.

In medical settings, it is used to make trays, counter tops and trolleys, as well as components in medical devices such as staple guns and other hand tools.

There are many uses in the automotive world too, with many small components such as hose clamps and safety critical components such as housings for airbag mechanisms and such. In the performance world stainless steel exhausts are commonly made from 316 grade stainless steel.

There are hundreds of applications for stainless steel in aerospace too, thanks to its resistance to corrosion and low temperatures, it is often used for pipework, bracketry and many other applications.

How to Work Austenitic Stainless Steel?

Stainless steel is relatively easy to manufacture but needs some extra considerations when compared to mild steel

• Machining: stainless steel needs a high feed, but low tool speed to cut without work hardening the material
• Corrosion: whilst stainless steel is corrosion resistant, if it comes in contact with mild steel, either by using mild steel supports or tools, the stainless steel surface can become contaminated, and oxidation marks will appear in time
• Heat and warping: stainless steel exhibits high thermal expansion, but relatively low conductivity, meaning parts can warp easily, if not allowed to cool, or sufficiently restrained whilst welding.

How is Austenitic Stainless Steel Made?

Stainless steels in general are made in similar ways to mild steel, with electric arc furnaces providing the heat to melt the raw materials, but stainless steel does differ in that a process called Argon Oxygen Decarburization is performed after the refining process.

AOD can be split into three steps, Recarburization, reduction Desulfurization. These three processes remove carbon, retrieve alloying elements such as chromium, and then remove sulfur, respectively.

After the molten stainless steel is produced with the correct alloying elements, the material is transported to different production processes depending on the end material shape; pressure or continuous casting is used to produce sheet and strip, and a slabbing mill is used to produce bars, sections and structural shapes.