Proper mokume billets, very brave. Only tried that once, but put
brass next to silver in the billet and had a catastrophic failure.
Assuming you oxidised the torque plate nicely before cranking the
billet together, the join, though soldered, is probably quite
brittle. Taking a cold chisel to the side of the billet, tip where
the billet meets the plate, and giving it a few taps might be enough
to break the join and not do any, well, much, damage to the billet
If you really really want to keep the billet you can also trim off
the edges of the torque plate, place it in a vice steel side up and
then grind off what remains of the torque plate itself, a bit
aggressive, but effective.
In future, try coating your torque plates with Tip-ex (liquid paper)
or some other anti-flux before clamping up the billet. Or use the
Alistair McCallum method (cheating, but it does work well) and solder
the billet together rather than relying on diffusion bonding under
pressure. This is how I do it, much easier to get binding wire off
then a steel plate and no specialist kit needed, also you get some
interesting blues when you put an ammonia patina on your work because
of the solder alloy
a 12 layer silver / copper / gilt metal mix, backed onto a silver
plate if memory serves). Happy to expand, but he explains it well in
one of the Mokume books, can’t recall which one now though.