Filler material for SS grades in high temp service

[XL83NL]

Hi Guys,

question: for applications where the operating temperature is in the range of (at least) 400 - 450 deg c,
someone (a welding expert who supplies Lincol Electric welding products) advised me to weld 304 to 304 using a 347 filler, 316 to 316 using 318 filler and welding 321 to 321 with 347 filler.
all this primarily due to IC @ say 400 deg C, and embrittlement starting @ 450-480 deg C. all these welds are for TIG-welding.

now, when I look temperature limitations of e.g. Thermanit H-347 (Böhler's 347 TIG-wire), it says max temperature up to 400 deg C due to IC.
when I look @ the Avesta version for 347 ('Avesta 347'), it may be used beyond 400 deg C, its especialy designed for such applications.

why do these manufacturers specify different ranges for the same type of filler material?

 

[Duwe6]

Another good choice for 304-304 is 308H as in High-carbon. Improves the high-temp strength.

As for the differences, the companies probably used different criteria to judge where unacceptable high-temp degradation started.

Sounds like your welding expert is correct.

 

[XL83NL]

Thanks for the reply Duwe6.
I wasnt really questioning the welding expert, but I found it strange 2 major filler material suppliers
seemed to give opposite recommendations for high temperature applications in these SS grades.

 

[metengr]

Look at the service environment, and not just temperature.

 

[EdStainless]

At high temp do you want strength or do you care about intergranular sensitization?
You have to pick one or the other.
And hence different recommendations.

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Plymouth Tube

 

[moltenmetal]

Generally, you're worried about the sensitization and IGC when the unit comes back down to low temperatures and baddies condense out. 400 C is the temperature at which the carbide precipitation takes place- it is not the temperature at which the IGC itself is the concern.

If your parent metal is not a stabilized grade, all the filler metal in the world isn't going to save the HAZ from sensitization, so I'm not sure what the point of bumping up to a stabilized filler metal would be.

So as EdStainless put it, you either want the strength at temperature (i.e. a matching filler metal to the base metal, irrespective of sensitization concerns), or you want a different parent metal AND weld metal.

I don't know the limits of 347 off the top of my head, but I think 1000 F (i.e. a fair bit higher than your 400 C) is where you need to kick over to H grade materials for 304, 316 and 321. Below that you can use dual grade materials (i.e. 304/L and 316/L) and avoid the sensitization concern- unless your process itself is carburizing.

 

[XL83NL]

Hi guys,

Thanks for all the replies. Ive been out of office some time, just picked my work up again, and noticed I didnt really replied anymore, even though I noticed some of the very useful replies.
As for switching to the H-grade; 321 here is readily available as 321/321H dual certified. And for the higher temperature applications we generally switch to 321, so we're pretty safe on that one concerning IGC. The filler for 321/321H will then be a 347Si (Nb-stabilized). So reading all the replies, we're pretty safe then, right?
Thanks again for the useful info.

 

[metengr]

Yes.

 

[Duwe6]

and another "Yes"