I would also like to share my similar past experience on ferrite.
Higher cooling rate reduces the ferrite.
Also if the welder uses higher currents, there is slight loss of Cr and depletes the ferrite number.
If the welder welds with a long arc gap there is pickup of Nitrogen and thus the Nieq. increases,and ferrite number reduces.
This we had encountered with the same batch of electrodes in one particular ASS job.
Hence jobs requiring ferrite control have to be welded with correct paramteres like current,Interpass,short arc gap,etc.. as per WPS
Normally a ferrite level of 4FN min. is recommended to avoid hot cracking.This can be achieved by adjusting the composition of base metal and filler material to obtain a microstructure with a small amount of ferrite in the austenite matrix.
Ferrite can be best determined with a magnetic instrument like Ferritescope, the Magne gage, calibrated to AWS A4.2 or ISO 8249 OR the WRC 1992 diagram.
Also note that ferrite has to be measured after welding and not after PWHT if any.
Regards
Prem Nautiyal
Godrej,Mumbai.
On Tue, 21 Jul 2009 19:45:55 +0530 wrote
>Yes higher heat input, Higher current, cleanliness of joint, will increase
>Ferrite no ,Generally use short arc
>
>
>
>From: materials-welding@googlegroups.com
>[mailto:materials-welding@googlegroups.com] On Behalf Of Singh Rishi (TIPO -
>QA/QC)
>Sent: Tuesday, July 21, 2009 4:49 PM
>To: materials-welding@googlegroups.com
>Subject: [MW:2735] RE: 2733] RE: 2729] Ferrite Number (FN) for the deposited
>weld metal
>
>
>
>Thanks Mr. Hegde,
>
>Can heat input , be a variable for erratic ferrite no ?
>
>For example I'm using filler wire of the same batch no ( packet ) & welder ,
>but in one joint I get Ferrite no. less than 8 % and in other joint I get
>over 10%.
>
>
>
>Best Regards,
>
>Rishi Raj Singh
>
> _____
>
>From: materials-welding@googlegroups.com
>[mailto:materials-welding@googlegroups.com] On Behalf Of PB HEGDE
>Sent: Tuesday, July 21, 2009 1:57 PM
>To: materials-welding@googlegroups.com
>Subject: [MW:2733] RE: 2729] Ferrite Number (FN) for the deposited weld
>metal
>
>
>
>
>
>
>
>Austenetic SS used in chemical /petrochemical plant require good Corrosion
>resistance. For which delta ferrite plays the major role.
>
>i)Increase in Delta Ferrite will reduce the corrosion resistance . Therefore
>in severe corrosion resistance requirement , ferrite to be kept below 8%
>(Generally it is kept between 3-7 %)However very low ferrite causes
>defect like hot crack, fissures ,There is no code requirement but Ferrite
>requirement is decided by process licenser ,depending upon the service
>condition
>
>ii)You can check ferrite No by Instrument called Ferrite Meter where you can
>get Ferrite No directly ,Some time You can check with respect to Delong
>Diagram ( Given in ASME Sec 2C ) by calculating /plotting the Cr , and Ni
>equivalent from actual chemical analysis of weld
>
>iii)My experience -some time Ferrite no increases due to work hardening of
>material If you measure by Ferrite meter
>
>Regards
>
>
>
>Hegde P.B.
>
>09714714803
>
>
>
>From: materials-welding@googlegroups.com
>[mailto:materials-welding@googlegroups.com] On Behalf Of tong tong
>Sent: Monday, July 20, 2009 9:31 AM
>To: materials-welding@googlegroups.com
>Subject: [MW:2729] Ferrite Number (FN) for the deposited weld metal
>
>
>
>Dear All,
>
>Regarding above mentioned subject, i would like to know in detail about
>ferrite number. I have a few questions to ask such as What is the ferrite
>number? Why it is so important? Materials subjected to ferrite number?
>Permissible limit of ferrite number? Code and standard that we refer to
>requirement of ferrite number? Procedure to perform ferrite number?..If
>anybody have experience or information regarding this subject hopefully you
>can share with me. Thank in advance for your kind cooperation
>
>
>Regards
>tong2
>
>
>
>
>
>
>
>
>>
>
PREM S NAUTIYAL
CELL : 9820313278
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