cold chisel

So called because it was used for cutting cold metal, as distinguished from a blacksmith's chisel for cutting hot iron.

cold chisel (plural cold chisels)

1. A narrow chisel, made of hardened, tempered steel, used for cutting stone etc.
   • 1928, Lawrence R. Bourne, chapter 2, in Well Tackled!‎:

     Meanwhile, Macpherson stood just outside the door, holding a cold chisel which he had taken from a dungaree pocket […] and there Mr. Willison found him.