Up to FN 10 is considered equivalent to % ferrite. You can specify 2-8FN, when FN is measured with instrument calibrated to AWS A4.2 or ISO8249
It can also be estimated from the chemical composition with the use of several diagrams. the oldest is 1948 Schaeffler diagram. The Schaeffler diagram is outdated now because it does not consider the N effect. an improved version to this is 1973 WRC-Delong, which can be used to estimate % ferrite. the main difference is WRC-Delong includes nitrogen(N) and show FN in addition to % ferrite.
The most recent is 1992 WRC diagram replaces WRC-Delong diagram in ASME 95 edition, considered most accurate as on date. FN can directly be measured on welds by using magnetic propertied of ferrite.
The WRC subcommittee also adopted the term FN to be used in place of % ferrite to clearly indicate the measuring instrument was calibrated to the WRC procedure.
However it is also the opinion of WRC subcommittee, it has been impossible to date to accurately determine the true absolute ferrite content of weldments
You may refer earlier posts in the group (MW 500, MW504 etc.) in this subject.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Agrawal Sunil (Mumbai -Stequ)
Sent: Thursday, April 01, 2010 8:35 AM
To: 'materials-welding@googlegroups.com'
Subject: [MW:4652] Ferrite Number Vs Ferrite Content
Can anyone guide me what is the difference between Ferrite Number and Ferrite Content?
Our client has asked for ferrite content to be limited within 2 to 8% is SS. Whereas our Licensor (KBR) practice is to specify the FN (ferrite number). What value (FN) our Licensor should specify in their process datasheet which is equivalent to 2 to 8% ferrite content?
Please guide me.
Best Regards,
Sunil Agrawal
Tecnimont ICB
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