Ferrite % vs Ferrite No 1

[Flareman]

I posted a question regarding the difference between Ferrite% and FN at thread288-34135. If you would be kind enough to visit that link for a response I would appreciate your help.
Thanks
David

 

[TVP]

The following is from ASM HANDBOOK Volume 6 Welding, Brazing, and Soldering, available from ASM International at

http://www.asminternational.org:

Ther term Ferrite Number, designated FN, has been adopted as a relative measure for quantifying ferrite content using standardized magnetic techniques (Ref 20). The FN approach was developed in order to reduce the large variation in ferrite levels determined on a given specimen when measured using different techniques by different laboratories. FN approximates the "volume percent ferrite" at levels below 8FN. Above this level, deviation occurs, where the FN value exceeds the actual volume percent ferrite. For example, a weld metal with 16 FN contains approximately 13.8 vol%.

Reference 20 is "Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Austenitic-Ferritic Steel Weld Metal," AWS 4.2-91, AWS, 1991.

Weld-metal ferrite content can either be predicted using constitution diagrams, such as the WRC-1992 diagram (Schaeffler-DeLong), or measured using instruments that take advantage of the ferromagnetic characteristics of the ferrite phase.

 

[ThomasEun]

FN = Ferrite Number
Ferrite percent = vol% ferrite
(Fe) = wt% of Fe

FN = (vol% ferrite) x [-0.025813 (Fe)2 + 5.408679 (Fe) - 102.3902]/100

References
1. Welding Journal, 76(1): 24-s to 37-s, 1997
2. Welding Journal, 61(11): 352-s to 361-s, 1982

Thomas Eun