Dear teachers,

Would you be kind enough to explain to me the proper meaning of the expression in bold in the following brief excerpt from the Jules Verne’s “The Mysterious Island”?
“The sailor began by detaching the two barrels, which, being in good
condition, would of course be of use. Then the locks were forced with a cold chisel and hammer, and the lid thrown back.”

As a matter of fact I know the proper meaning of the expression in question on o.s own account namely “
a chisel made of hardened tempered steel and used for cutting cold metal”. I am at the loss concerning the meaning of the expression “cold metal”. I know only the meaning of the following expressions: cold steel and cold iron.

Thank you for your efforts.