Understanding the ferrite content of austenitic stainless steel

Ferrite Testing

At Format NDT Ltd we specialise in non-destructive testing. Our goal is to help our clients to identify the materials they are working with and look for any flaws within them. The aim is to maximise safety and quality. We are a one stop shop for NDT, offering everything from ferrite testing to UT and replication.

The ferrite content of an austenitic stainless steel is very important. There are several reasons why. Firstly, the ferrite is magnetic. That means if magnetic characteristics will hurt the performance of a product, the steel must have a low amount. In addition, in some environments a higher amount will affect the corrosion resistance.

How much ferrite is in the steel?

An austenitic stainless steel will usually have some ferrite when it is cast. It is necessary to help reduce the risk of cracking during cooling. The amount usually depends on the composition of the alloy. Higher amounts of things like carbon, nickel and manganese will reduce the tendency for it to form.

In 304 stainless steel castings, the ferrite content can range from around 8% up to 20%. Wrought 304 stainless can have between 1% and 6%.

Annealing can help to reduce the amount of ferrite by dissolving it. However, it cannot get rid of all of it in cast stainless. If you anneal a wrought stainless steel though, there will be very little remaining.

It is also important to keep in mind that the amount of ferrite can differ in weld sections. The welding process, and use of filler material can increase the amount. As a result, it can be around 5% to 10% depending on the alloy.

Do you need ferrite testing?

If you are worried about how magnetic a stainless steel is, Format NDT Ltd can help. We can provide testing to give you an accurate idea of the ferrite content. Our team have a lot of experience here and can effectively test raw materials, various parts, and welds too.

So, if you need any help, please contact us.