The Difference Between Austenitic and Ferritic Stainless Steel

Stainless steel railroads

Stainless steel is one of the world’s most commonly used materials. Consisting of iron, chromium and carbon, it’s found in everything from screws and bolts to automobiles, rockets, bridges, railroads and more. While all stainless steel contains these three elements, though, it’s available in different types. There’s austenitic stainless steel, and there’s ferritic stainless steel. What’s the difference between austenitic and ferritic stainless steel exactly?

What Is Austenitic Stainless Steel?

Austenitic stainless steel is defined by its crystalline structure. The term “austenitic,” in fact, refers to a crystalline structure. Like all types of stainless steel, it consists of iron that’s mixed with a small amount of chromium and carbon. Chromium is responsible for its corrosion-inhibiting properties. Austenitic stainless simply has a crystalline structure that’s reflected upon its unique characteristics.

There are two subtypes of austenitic stainless steel: 200 series and 300 series, both of which contain a small amount of nickel in addition to their standard iron, chromium and carbon content. 200 series austenitic stainless steel simply contain a higher concentration of nickel.

What Is Ferritic Stainless Steel?

Ferritic stainless steel, on the other hand, is defined by a chromium content of 10.5% to 30%. All forms of ferritic stainless steel are made of at least 10.5% chromium. Iron is the main ingredient used in their construction. Nonetheless, ferritic stainless steel contains a higher concentration of chromium than austenitic stainless steel.

It’s important to note that ferritic stainless steel can’t be hardened via heat treatment. Hot rolling, for instance, won’t harden ferritic stainless steel. Ferritic stainless steel can only be hardened via cold treatment, such as cold rolling. Even then, ferritic stainless steel is resistant to hardening. It may harden to some degree, but it won’t exhibit any substantial difference in hardness.

Comparison of Austenitic and Ferritic Stainless Steel

The main difference between austenitic and ferritic stainless steel is that the former features a crystalline structure, whereas the latter contains a higher concentration of chromium.

Another difference between these two types of stainless steel is that only ferritic is magnetic. Ferritic stainless steel contains a higher concentration of iron, which is responsible for its magnetic properties. Austenitic stainless steel contains a lower level of iron. With less iron, it’s typically non-magnetic

Austenitic stainless steel is also better protected against corrosion than ferritic stainless steel. It contains high levels of both chromium and nickel. These added elements help to protect it from corrosion.