On Mon, 05 Jul 2004 11:44:08 +1200, Eric Stevens wrote:
There is NO weld technique which produces a weld with metallurgy
identical to the the parent metals. ANY weld technique leads to a
discontinuity in material properties in or around the weld zone which
ALWAYS results in a propensity for the welded structure to fail in or
around the weld zone rather than the parent metal.

Incorrect. Consult a good welding text such as "Modern Welding" by
Althouse and Turnquist (the most widely used, and most authoritative,
welding textbook).

It is true that fusion welding produces a HAZ (Heat Affected Zone) around
the actual weld joint. This can significantly alter the properties of *some*
materials, namely medium and high carbon steels, some alloy steels, and
some aluminum alloys. But *part of the welding process* in those cases is
post-weld heat treatment to restore those properties to their original pre-
weld state. In other words, you haven't completed the welding process for
those materials until you've done the post heat treatment.

For materials such as mild steel, the most commonly welded material,
there is no such concern. The HAZ doesn't affect the material properties.
That's because mild steel has too little carbon in the solid solution to
produce the phase changes that could alter its crystaline structure.
A *competent* welder will also choose an appropriate alloy filler material
so that the fusion zone won't have different properties from the parents
either.

It is well to note too that different welding techniques produce differing
size HAZ. TIG welding produces less than arc, MIG produces less than
either, and exotic techniques such as laser welding produce practically
none at all.

Now you are postulating *cold welding* for the gage blocks, and that
produces *no HAZ at all*. So the material properties surrounding the
weld joint would not be altered *at all*. Of course cold welding isn't
what's actually happening when you wring gage blocks together, but
if it were, you'd still be wrong.

Gary