On Mon, 08 May 2006 10:30:28 -0400, Chuck Harris wrote:

big snip

Hi Scott,

Now I understand the question. It is impossible to prevent
hydrogen embrittlement when gas welding. A natural byproduct
of the combustion of oxygen and acetylene is water vapor, which in
the flame shows up as H+ ions. These H+ ions get mixed in
with the molten steel, and form a mess. These H+ ions turn
good steels into something that is full of glass hard fissures,
and will always crack... sooner or later. Gas welding is really
only suitable for mild steels.

If all you have is a gas rig, and you need to connect good steels,
like 4130, you should be brazing... which essentially is what you
are doing when you use a mild steel filler (coat hanger wire).
(don't really use coat hanger wire. Its a mystery steel. Its only
operating requirement is the alloy must be cheap and soft)

If you are trying to make a joint that is as strong as the base 4130
steel, you should be using a stronger filler steel, and a shielded
arc process. The best would be TIG, or MIG.

-Chuck



The desire to use TIG with a higher end rod and post heat treat is the
best but the question is answered correctly for a repair in structural
aircraft members where heat treatment is not possible would be with an
ER70 rod and OA welding. It was only a few years ago that the FAA
even addressed TIG in the AC43.13.

Mike