by Mike
(Atllanta)
i know 309 is a the best rod for this, but can i use both and need argon purge for both?
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308 filler wire wil definitely stick it together but for anything critical, 309 is the way.
309 is designed to compensate for dilution and still provide a good metal composition.
308 is not.
Argon purge is needed if the back side is molten or it will sugar and cause failure if the weld is under any kind of severe load.