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Up Topic Welding Industry / Technical Discussions / FN number for 317L weld
- - By GRoberts (***) Date 05-28-2002 16:23
We have some 317L SMAW electrode that per the manufacturers chemical analysis has a 5.9 FN (WRC), and we welded up a "weld button" (deposit 5-6 layers on a sst block), and got a 5.5 FN (good correlation with WRC) using a Fisher Ferritscope. Our customer wants results from an actual joint also, so we welded up a sample. (Base material is ASTM A351 CG3M). Chemical analysis on the weld reveals a FN or 6.8 on WRC, but Ferritscope test is Root FN = 15.9, Fill FN = 10.8, and Cap FN = 13.3. Why is the actual weld FN as tested with a ferritscope so far different than the WRC diagram in the second case? The Ferritscope calibration was also found to be very close to ideal. I need to keep the FN under 10 for this project.
Parent - - By Niekie3 (***) Date 05-28-2002 18:27
I must say that I also find it difficult to give a proper interpretation of your results, but here are a number of things that could help you understand the situation:

1)When welding the "button", you will have very close to an ideal weld metal reading because with 5-6 layers, you will have negligible dilution from the base metal. In addition, you probably have at least a thickness of 10 - 15mm of weld metal. This means that your ferritscope measurement will not be significantly influenced by the base metal.
2)When performing the "actual joint", you will no doubt have significant dilution from the base metal. In addition, the readings from the ferritscope will be influenced by the base metal.
3)I am not exactly sure what your material specification is, but looks like a casting spec. If this is the case, then there can be significant variations in the composition of this base material if it was not properly heat treated. This can significantly influence the weld composition and ferritscope readings.
4)An interesting piece of info. that I found from Avesta literature: Their 317L TIG/GMAW wire has a typical FN of 5, while their 317L SMAW electrode has a typical FN of 10 even though the nominal chemical composition is the same. (If someone can explain this, then please tell me!)

Hope that there is a usefull idea that can help you in the above.

Regards
Niekie Jooste
Parent - - By GRoberts (***) Date 05-28-2002 19:05
Niekie,

Thanks for your input.

The dilution from the base metal is factored into the WRC FN obtained from the welded joint, as we put the weld metal on our spectrometer to obtain the chemistry used for plotting on the WRC diagram. The base material is a casting. (I work at a foundry) We have done ferrite testing before with 316L electrodes and generally do not have this discrepancy between the WRC diagram and the ferritscope. I think you may have a point though when you say "the readings from the ferritscope will be influenced by the base metal." I don't know, but I wonder how far from the probe that the ferritscope is measuring. I believe the ferritscope is an eddycurrent based machine, but I don't know the size of the area that is being measured when it gives me a reading. Does anyone know this? I hadn't noticed the difference between bare wire and SMAW electrodes either. Interesting.
Parent - - By Niekie3 (***) Date 05-29-2002 19:49
How did you weld up the "button"? Was the final layers that you welded on this test piece done with the temperature quite high? If so, the low cooling rates could have resulted in much of the ferrite transforming to austenite. If on the other hand, your weld simulation was performed at a much lower temperature, you could have more retained ferrite.

Another possibility is that the arc length differed significantly between the two tests. With long arc lengths, you could have more N pick-up which would result in lower ferrite numbers. (N is a strong austenite stabiliser.)

Regards
Niekie
Parent - - By GRoberts (***) Date 05-30-2002 14:55
Update: I had a piece of all weld metal cut from the actual joint weld, and the FN was the same as when it was still attached to the base metal, so I would say that the ferritscope is not influenced by nearby material. The area it is measuring must be farily small. Also, the weld buttons we cool in water between passes, and the weld joint was cooled below 300F interpass temp. I can't comment on the weld button, but the arc length for the joint resulted in about 27 volts with 5/32 electrode, so it was fairly normal. I think I will see if the weld button was retained for chem analysis next.
Parent - By Niekie3 (***) Date 05-30-2002 18:20
I must admit that I am at a loss to provide any further ideas. If you manage to figure it out, let us know so that we can also learn from your experience.

Regards
Niekie

P.S Are you sure there was no mixup with the electrodes? Have you performed chemical analyses on both samples?

Up Topic Welding Industry / Technical Discussions / FN number for 317L weld

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