Re: [ihc] My Christmas Present

["Jim or Ginger Aos" <jaos@xxxxxxxxxxxxxxxxx>]

----- Original Message ----- 
From: "william cunningham" <slypigs@domain.elided>
To: "John Hofstetter" <hofs@domain.elided>
Cc: "Dave Nuenke" <dnuenke@domain.elided>; <DeepSouthScouts@domain.elided>;
<ihc-digest@domain.elided>
Sent: Sunday, January 04, 2004 8:36 PM
Subject: Re: [ihc] My Christmas Present


> I have yet to convert to gas, all of my work is done outside in the wind
so
> flux-core is the way to go. Once I get both girls through college, and
build
> a 30X40 shop where I can work out of the weather I will hook up the
weldmix
> (gas).
>
> I have some welding to do on the rear bumper of  the SS II but given its
> proximity to the gas tank I have avoided the chore, now with the temps
> running 20 to -10F I think that welding near the tank will be safer, less
> likely to blow up!
>
> Should I pre heat the metal when welding in temps this low?
>
> Willy
Bumpers and frames are built with alloy steel.  That means they are subject
to heat treating.  The amount is dependant on the carbon equivalent ratio of
the alloy/s.   The first stage of heat treating is getting the steel up to
the austenitic condition, 1350 to 1700 f.  Step two is quick cooling (
relative), that brings it to the hard brittle stage( martensite).  Step
three is the tempering ( controlling), drawing,  process. That changes the
brittle to hard and tough, or normalized, or soft and malleable ( annealed).
That is a condensed version of heat treating.  Better explained in a half
day session, or even a full 30 hour class session.

If you preheat the steel you slow the quenching process and go directly to
the finished step, tough, normalized, or annealed.  Timing and cooling rate,
are the main critical factors.  Tig welding, due to the slow heat input a
natural way to accomplish the preheating purpose, along with gas welding.
The next best is stick with a 7018 electrode (rod), after that dual
shield,( usually to heavy for light materials.  The process that heats
quick, moves fast and cools quick, is the wire feed. This one should have
pre heating.  Usually 200 to 400 f., and can be estimated by a pine stick
chars at about 400f , solder melts at about 360f., and oil smokes at around
the same.
High alloy steels T-1, Chrome moly, 4140, etc. are much more sensitive to
proper heat treating procedures.

The colder the temp the more the need for preheating.  And stay out of the
wind (a quenching process).        Whenever in doubt, PREHEAT.

This is likely more than you asked for, if not more info is available.  Jim
A. retired Welding Instructor