Mark Stonich wrote:

4130 filler rod.

ER80-S2 is usually used with plain "Aircraft grade" 4130. See
http://www.lincolnelectric.com/knowl...hrome-moly.asp

However, an increasing number of bike builders are using a stainless
filler, Weld Mold's Polytensile 880. http://www.weldmold.com/800.htm
It welds very nicely and has good mechanical properties, 110 kpsi and
35% elongation. It's expensive, about $15/lb. But a whole bicycle may
only need 3 or 4 sticks of 0.035" diameter rod. (When you are trying
to save grams, you don't go broke buying filler ;-)

That sounds a lot like 312 Stainless which is marketed as a superalloy
by a number of vendors. A discussion here on stainless fillers for
various steels suggested that 309 is almost as strong, less subject to
cracking and much cheaper. 309 runs around 95Kpsi. Try it.

Ted