glen,
the process of heating to cherry red hot and allowing to cool is referred
to as "normalising". it's required to relieve the odd difrences between
the weld and surrounding metals. if it is not normalised after welding it
will tend to crack around the welds! it's a required procedure after any
electric welding on rollbars so they will not colapse , failing at the
welds! gas welding usually cherrys the surounding metal enough to do the
stress relief . but any form of electric welding causes (usually)
beautifuly done welds but yeilds serious brittle areas adjacent to the weld
wich if either exposed to some kind of stress or heat cycling will lead to
fractures adjacent to the weld.
chuck
> [Original Message]
> From: Glen Byrns <grbyrns@ucdavis.edu>
> To: <spridgets@autox.team.net>
> Date: 3/7/2006 5:25:31 PM
> Subject: metallurgy question
>
> I'm going to be welding up a manifold from mild steel tubing, three short
> stubs of 1.25" going into a 'log' 2" in diameter. This will mate a turbo
to a
> 1275.
>
> My question is, would the finished manifold be less likely to crack if the
> manifold is heated up to red heat and cooled slowly before use? The
original
> was made by the PO and has cracked at the welds several times over the
years.
> This one will be a copy made with thinner gauge steel. I presume the
cracks
> are from the stress of the 'log' expanding as it gets hot, while the
faceplate
> bolted to the head is much cooler and doesn't expand nearly as much.
Would
> thick or thinner steel be less lkely to crack in this situation?
>
> Once I finish this one for the bugeye, I plan to design one to mate a
modern
> small turbo (VW?) to a 948 (Austin Powerless).
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