304 to 321

[fill&cap]

hi guys
i got a small one off job to do 304 tube to 321 round
i know the ussual wire for this would be 308.
can these two materials be welded with 309 or 316 none critical applications.
the job dosent warrant buying a full tube of 308 ,unless more 304 work comes in this month .

cheers jay

 

[Hitch]

Going back quite sometime, we did a lot of various stainless in 304 and 321, i seem to recall using 347 wire.....

The 347 over 308, because of the 321.....
If its non critical, i cant see a reason why not...someone else might though...

 

[sm-]

Hitch is spot on. As a rule of thumb you choose filler based on the highest alloy number
So say 304-316 316 wire is the one to use because it will "overalloy" the 304 but match the 316 the otherway around the 316 would be "under alloyed" and therefore pointless to use it. So if its non critical you could probably get away with the 316 but you will have no use of the 321`s higher properties

 

[TechnicAl]

sm

I actually think the opposite. The job is only as good as the "weakest" component so whats the point in overmatching. Take the OPs question. If it fails it will fail in the 304L as its "weaker" than the 321. Therefore the joint only needs to be as "strong" as the the 304L.

Im using "weaker" and "stronger" as a catch all for the properties including corrosion

 

[sm-]

I am only going on what on old boss of mine always told us when doing these kind of jobs, His reasoning was that by doing it this way you would get little bit better properties at the joint of the weakest metal sort of the same when using 309 or 312 for dissimilar joints. But i know not everyone saw it this way. But these sort of jobs where usually only installed for a very short time before we changed the parts.

Just a couple of questions then because i know u got real knowledge of this

1.When joining dissimilar steel then why use 309 or 312 insted af the ss parent grade. If using the strongest-weakest reasoning then the extra alloy is really of no use other then maybe give it a little longer lifespan?

2. Why does Hastelloy usually work really good when used as "Maintenance/emergency" repair filler if you dont know the material grade.


This metallurgy is intresting.

 

[TechnicAl]

309 is 23/12 so when diluted by Mild Steel it becomes 19/9 or thereaboiuts. Thats the theory. In other words it can stand dilution by mild steel yet maintain a ductile structure. If you used 19/9 (304L) the dilution would produce a brittle structure.

312 (29/9) can accept even higher dilution levels than 309L and its a lot stronger....but it does suffer from embrittlement if heated so very thick joints can be a problem as is anything that is heat treated after welding.

Hastelloy (which is a trade name) is a high Nickel Alloy that has similar dilution resistance to 309L only more so. It will retain its original structure (which is ductile) no matter what you do (within reason). The problem is........... these alloys are very expensive....probably 10 times dearer than 309L

 

[Hitch]

The 347 has better properties for use in hotter environments.... we were using it on stuff for an incineration plant.

 

[sm-]

Well i found this intresting so i doug out the Avesta welding handbook.

And as Hitch said the 347 is recommended if the working temperature exceeds 400 degrees celcius. Otherwise you could use 308l i think it had something to do with the niobium content in the 347.

But i am sorry to say they disagree a bit with Technical Al

direct quote from the book

When welding two different stainless steels to each other, the choice of filler metal is normally determined by the more highly alloyed of the two parent metals. For example, when welding1.4307/ASTM 304L to 1.4404/ASTM 316L, a 316Ltype filler should be used. However, as shown in table 12.2, there are exceptions.
End quote

Is 316 different because of its Molybdenum content ?

And on the other 3series stainless you could go with the lower number because of their lack of Molybdenum?

Technical Al thanks for the explanation on the other questions.
I have learnt that if you dont ask you dont learn.



Putting in a link for the table mentioned in the text

http://www.avestawelding.com/pages/Page____365.aspx

 

[TechnicAl]

I dont agree..........why would you use 316L to weld 304L when the 304L will fail first. The 308L weld will have better corrosion resistance as it will be slightly higher alloyed 308L weld metal is 20/10 whereas 304L is 18/8. 316L is more expensive. To me its a waste of money for no gain.

I dont know why they are recommending 316L

316L is 19/12/3L the 3 being Molybdenum

The 347 is for high temperature but only if its 321 to 321......They are really the same alloy but 321 is Ti stabilised and 347 is Nb stabilised but its just a different way of doing the same thing. Its not possible to make 321 weld metal....you lose the Ti whereas Nb will pass across an arc.

 

[TechnicAl]

Incidentally Ive just had a look and Rolled Alloys and Sandvik are both saying 316L

Id like to know why?

 

[fill&cap]

cheers for that guys, il order 5kg of 308. it will always get used .
just been one of them months were its all spend spend spend on materials and nobody wants to pay me on time for the work thats been done.

cheers f&c