The only bad metal I've read for them so far has been anything with zinc.
Excerpt from my read:
"Soak it in a tub full of a mixture with 50% Vinegar and 50% water, this will neutralize any zinc remaining on the cage wires after weld. Cages galvanized with zinc are toxic to Chinchillas, zinc itself is toxic to Chinchillas, cages galvanized after weld are generally not galvanized with zinc but it’s a good idea to neutralize it just in case."
That, is all I've ever seen on metal.