Max FN for 316L and 304L

[Gem1]

Hi All,

Despite reading many references on the net and in these forums I'm still confused about what maximum Ferrite Number I should specify for welds between 316L or 304L. This is for structural welding which will be in service at the coast. The electrodes being used are as pre-qualified (by AS 1554.6) for the alloys - i.e. 316L and 308L respectively.

General consensus is that you need a minimum of 3 or 4 to prevent cracking, but what about the upper limit? I have seen anything from 8 to 15 when reading different things. At what point does the ferrite content start significantly degrading corrosion resistance of the weld?

How does the recommended range change if you are doing a dissimilar weld to a structural steel?

Thanks,
Gemma

 

[stanweld]

The maximum ferrite content is normally not specified for the items defined; it is for welded items in cryogenic service or for items in high temperature service.

 

[EdStainless]

For low temp because the ferrite gets brittle.
For high temp because it turns into sigma and gets very brittle.

Not for general as welded because there is no zone where you have enough to help with weld integrity and yet not too much for corrosion issues.
In SS that is annealed after welding there is often a limit of 0.5% in critical corrosion situations.

Don't worry about the max. It is more important to fist get sound welds.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[jwhit]

With these fillers, you will typically see around 10by WRC-92 diagram. I have often seen customer specs allowing up to 20FN ferrite. From my understanding, except for low mag permeability or low temp. work 5-10 seems to work well at eliminating cracking. I have also been told that over 20 can lead to cracking, not sure of the mechanism. In the 5-10 range the ferrite pools stop cracks from extending because of greater strength at room temp.than the austenitic matrix.

 

[Guest102023]

At 20FN it stops being austenitic and becomes more like duplex. I have not heard of cracking from that though.

I have encountered many ranges, but anywhere within 3 min. (not lower) and 10 max. (not higher) will suffice for general applications that are neither cryogenic nor high-temperature. The 308L deposits I have tested have not strayed much from 7-8FN.

 

[jtseng123]

how high is considered "high temp" ? We have service at 1450F and FN is 3-10 per spec, and 3-8 provided by supplier.

 

[Gem1]

Great feedback, thanks everyone. It seems like most of you think looks like I don't have to worry too much about a maximum in my structural, ambient temperature application unless i'm getting higher than 15.

brimstoner, where did you get your 10 max from? Is it experience or a reference? My fabricator is getting results of 9-12, which i'm inclined to accept, I was thinking about setting a range of 4 to 12 or 15.

 

[metengr]

The 9-12 FN range is normal and typical.

 

[SJones]

ISO/TR 17671-3 states:

Consumables for standard austenitic stainless steels are generally designed to result in a ferrite content of between
3 FN and 15 FN in the as-deposited fusion zone, for enhanced resistance to hot cracking.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[stanweld]

The values stated by SJones are pretty much typical for E/ER308L with the maximum a bit lower for E/ER316L filler metals. Tighter ranges (3 to 8) can readily be purchased.

 

[Guest102023]

In my experience the common 3xx grades from quality manufacturers are formulated to consistently fall within quite narrow ranges of only 3-4 points FN. When the correct grade is selected for the corresponding base metal, hitting the specified range should be nearly automatic. 308L deposits should never get near 15FN at the high end or 3FN at the low end.

When I was doing development work for SS overlay I noticed how consistent the Cr and Ni contents of ER309L were from various suppliers (of course there are more suppliers than actual manufacturers, which partly explains it).