Ferrite Number of Stainless Steels

[ahassan86]

Dear Experts

How often should I perform Ferrite Test on Autenitic or Duplex STSTs (Test Frequency)? Should I perform it with every new consumables batch? Should I perform it periodically regardless of any changes? And what are the preferred ranges in terms of FN for both Auten. and DSS?

Thanks

 

[metengr]

Typically, during weld procedure qualification for a project using duplex stainless steels, the volume fraction of ferrite is determined by metallographic examination of the weld coupon used in procedure qualification to ensure a proper austenite to ferrite phase balance for the weld metal (40-60% by volume ferrite). If the procedure qualification is acceptable along with supplemental testing using ASTM A923, production testing of ferrite number is really of limited value.

For austenitic stainless steels, there is really no reason to measure the ferrite number, unless there is a mix-up of consumables or lack of quality control on the job.

Ferrite determination of field welds can be difficult, especially for duplex stainless steels, and may yield erroneous results unless a procedure is established using a magnetic ferrite gage and confirmed via metallographic examination (for duplex stainless steels).

Please review the attached document for duplex stainless steels, and especially review 6.2.4;

http://www.worldstainless.org/Files...he_Fabrication_of_Duplex_Stainless_Steels.pdf

 

[EdStainless]

It usually requires a very large job to require more than a couple of tests.
That said it is much more important in a DSS than Aust.
With Aust it is controlled by the filler chemistry.
In a DSS any change in heat input/weld temp will change the F/A balance.
Often you see the weld qualifications (both process and for individual welders) tested per A923 and micros.
In process checks may be done with field magnetic tests or some other secondary non-destructive method.

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