Re: [ihc] My Christmas Present correction

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

big snip---
> >
> > 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).

Step three is a reheating process range from 400 to 1200F depending on alloy
content.  Improper proof reading.  Jim A.

> 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