Hi Sunil,
Mr. Bathula provided a very detailed reply to your query.
Delong Diagram, is a modified Schaeffler Diagram predicting the Ferrite Number (FN) up to a maximum of 18 FN. The diagram includes the nitrogen level into the calculation to predict the FN (which was not included in Schaffler diagram).
Delong diagram provides a better correlation between the calculated and measured ferrite content of the weld metal. Typically 8% volume fraction ferrite would equal 8 FN. Beyond this value typically, Ferrite No would be more accurate. However as per AWS and other WRC documents Delong diagrams upper limit is up to 18 FN or typically 15% Ferrite.
WRC-1988 and later version (1992) diagrams are most accurate and preferred diagram for predicting the ferrite in “300” series stainless steel weld metals. The advantage of this diagram is that it provides readings in a wider scale in Ferrite No (FN).
The best and most accurate method for ferrite measurement is as per ASTM-562, and expressed in volume fractions (% Ferrite) however is time consuming. From your experience you may have seen that Ferrite No and Vol % Ferrite readings are asked often for Duplex Stainless Steels.
Hope the above would provide further clarifications to you query. The WRC and Delong diagrams are explained in this attachment.
Thanks
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Component Integrity Section.
Engineering and Training Services
Ontario Power Generation Inc.
Res:-88,Garth Trails Crescent
Hamilton,Ontario, L9B2X1,Canada
Tel-905-679-9677
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Bathula Raghuram (Mumbai - PIPING)
Sent: Thursday, April 01, 2010 1:15 AM
To: materials-welding@googlegroups.com
Subject: [MW:4656] RE: 4652] Ferrite Number Vs Ferrite Content
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 The Schaeffler diagram is outdated now because it does not consider the N effect.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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