TIG Filler rods

[knoba]

On a recent thread about the compatibility of tig filler rods on stainless steel, DIY Welding wrote:

DIY Welding

The main difference is the carbon content; a 308 has 0.08 carbon, in the 308L it is 0.03. You need the L type for tig filler. You can get a problem called crocs if you use 308

What is crocs? I can't find it on google or anywhere else. Can anyone point me in the right direction please?

Also, are the recommended fillers, for different grades of stainless steel; ideally suited or just the most cost effective solution (ie. is it ok to use 316LSi filler on 304L)?

 

[hotrodder]

Not heard that term before, guessing probably a slang term- for example forgetting to purge a stainless weld may result in a 'coked' weld in the UK, in the US it would be a 'sugared' weld

I'm guessing 'crocs' probably refers to carbide precipitation. The link covers corrosion resistance of stainless steels in general, 'intergranular corrosion' is the relevant bit.

 

[knoba]

Thanks hotrodder! (I kept thinking it might be something to do with; carbon imbalance / corrosion / contamination?) I reckon you're "right on the money". The link you gave me is fantastic, as I've not had a really good look around azom before.

 

[hotrodder]

There's a lot of good stuff there (found a good one on titanium fabrication when googling for info on sand bending the stuff the other day) although http://www.bssa.org.uk//topics.php is better for stainless specific info

Forgot about the different fillers, the common austenitic alloys are modifications of the basic alloy, adding a little molybdenum to 304 for example improves corrosion resistance in chloride environments- this is 316. That's not quite the full story but pretty close

For 'general purpose' work using a 316 filler to weld 304 is ok, obviously if the corrosion resistance or other properties are more critical then the filler needs to be matched to the base alloy(s) and service environment

304 welded with 308
316 welded with 316
321 welded with 347 these are 'stabilised' (contain a little titanium and niobium respectively) to prevent carbide precipitation- the Ti and Nb have a greater affinity for carbon than chromium does so the carbon content can be left alone resulting in better strength at elevated/fluctuating temperatures

L is low carbon (often sheet/tube etc carries a dual designation 304/304L)
H is high carbon (pretty specialised uses)
Si means increased silicon which improves weldability- wets out better

 

[Pete.]

321 welded with 347 these are 'stabilised' (contain a little titanium and niobium respectively) to prevent carbide precipitation- the Ti and Nb have a greater affinity for carbon than chromium does so the carbon content can be left alone resulting in better strength at elevated/fluctuating temperatures

Probably why 321 is so good to use for turbo manifolds. Shame it's so damn hard to get hold of though..

 

[knoba]

I must admit that I find some of these technical aspects rather hard going. Thanks again for all the info chaps. I'll try digging into some more reading matter!