What is Ferrite Number in Welding?

Ferrite Numbers (FN) are the current industry accepted figures for specifying ferrite content in the austenitic stainless steel weld metal, as approved by the Welding Research Council (WRC), American Welding Society (AWS), and other organizations.

The FN is a measure of the austenite stabilizing elements in the weld metal, i.e. chromium, molybdenum, silicon, tungsten, and nitrogen. It is reported as a range from 0 to 100 and is determined by calculating the amount of each element in the weld deposit and converting this information into FN units. The lower the number, the greater the ferrite content in the weld metal.

The importance of ferrite content in austenitic stainless steel welds has been known for many years and is related to several factors, most notably corrosion resistance and mechanical properties.

How do I find my ferrite number?

If you want to know the ferrite number of your austenitic stainless steel weld metal, you can use a simple calculation. First, you need to know the percentage of each element in the weld deposit. Once you have that information, you can convert it into FN units using the following formula:

FN = (%Cr) + (%Mo) + (%Si) + (%W) + (%N)

For example, if your austenitic stainless steel weld deposit contains 16% chromium, 10% molybdenum, 1% silicon, 0.5% tungsten, and 0.2% nitrogen, the FN would be:

FN = (16) + (10) + (1) + (0.5) + (0.2)
FN = 27.7

This FN indicates that the weld deposit has a higher ferrite content than most austenitic stainless steel welds, which typically have an FN of 30 or less.

What is ferrite level?

The ferrite level is the amount of ferrite in a material, typically expressed as a percentage. For austenitic stainless steel welds, the ferrite level is directly related to the FN. The higher the FN, the lower the ferrite level (and vice versa).

Ferrite number calculator

There are a number of online calculators that can be used to determine the FN of your austenitic stainless steel weld deposit. Simply enter the percentage of each element in the weld deposit and the calculator will do the rest.

Ferrite number in 316l stainless steel

The ferrite number of 316L stainless steel is typically between 30 and 35. This means that the weld deposit will have a lower ferrite content than other austenitic stainless steel welds, which is desirable for many applications.