Filler metal selection for welding mild steel and 4130 tube

[EchoSixMike]

ER70S2 is the usual TIG rod; 70S6 is a normal MIG wire. You don't need the extra silicon for TIG S/F....Ken M

[Rambozo]

ER70S2 is the usual TIG rod; 70S6 is a normal MIG wire. You don't need the extra silicon for TIG S/F....Ken M

A lot of people use S6 for 4130 because it wets out better from other properties of the silicon besides deoxidizing. In some places it works quite well. I also prefer S2, but mainly because I think it handles out of position welds better. You will find plenty of people that swear by one or the other. Just like some people use 70S2 MIG wire for clean metal welding.

[Spike]

s2 vs s6 isn't much of a difference. each welder will find what works better for them in different situations. s6 is what i got used to and got good with because almost everything i do has to deal with widely varying metal thicknesses, and i often get stuck with dissimilar alloys being welded together. The wet-out properties and deoxidizing properties of s6 work better for me.
As far as makeup go, s6 does have like twice the silicon and manganese of s2... but that's only 1% of the total makeup. s2 is 97% iron, and s6 is 96% iron, so for all mechanical intents and purposes they are equal, it's pretty much just the 'puddle characteristics' that differ.