There's no logic in the argument that you must smash before you
smash.
There may be, however, even if not obvious. A rolling mill exerts
even pressure across the whole width of the ingot. In so doing, the
pressure is also linear along one axis, and, because it’s spread over
a fair width, the pressure at any given point may not be quite as
much as the impact force of a hammer. That will result in the
deformation being more at the surface, not penetrating as far into
the sheet. When rolling sheet, it is common to find the ingot
curling a bit with the process, sometimes getting decidedly wavy.
Part of the cause of this, in addition to slight inaccuracies in the
rolls, is that the deformation is more at the surface, stretching it
more than the interior, which you can easily see at the ends, which
develop a hollow depression as the surface stretches more than the
core. As you roll, that greater deformation of the surface, hardens
it more than the core, so then subsequent passes transfer more energy
to the center, and eventually the stresses at the core from
deformation equalize with those at the surface, even if that hollow
depression didn’t go away. The clue to this is that often, that
waviness in the rolled sheet evens out again, becoming if not flat,
at least a lot closer to it than it had been. That, by the way, is a
good time to anneal. But in any case, the observation is that when
rolling, stresses are directional, and more at the surface.
A hammer blow, on the other hand, transmits force into the metal at
one spot, radiating more evenly in all directions. Or at least more
so than is the case with rolls, even if a cross peen hammer is used.
More, the higher impact force of a heavy forging penetrates deeper,
more to the center of the ingot, so unevenness in internal stresses
for forging can be less than with a roll. That results in a more
uniform working of the ingot in the initial stages, which can lessen
the chances of cracking. This is aided as well by the fact that when
forging, one does not need to forge quite out to the edge, which can
be weakest and most easily cracked. The metal at the edge will still
stretch, pulled by the rest of the ingot, but more gently and slowly.
Once the ingot has been worked enough to harden it up a bit and
deform the crystal structure, then annealing allows the metal to
recrystalize into a structure with more even smaller crystals, which
is stronger and then is less prone to crack when rolled. The overall
structure ends up with less of a “laminated” sort of structure, even
after rolling and annealing.
But back to the original thread, of forging 22K gold. I can imagine
if the alloying metal is only copper, that a 22K gold might be hard
enough to require this. But frankly, I doubt it. 22K is so soft and
malleable that it’s pretty forgiving. Not like 24K, but not that far
behind either. I seriously doubt that going straight to a rolling
mill with 22K will give you significant problems over forging it
first. If it did, I’d suspect contamination of the metal during
melting with some other metal not normally alloyed with gold that
can make it more brittle than usual. Iron, Tin, Lead. Or?
Peter