Haynes Ultimet description: A cobalt-based, solid wire, ULTIMET wire is used to weld ULTIMET wrought products, and more importantly, to overlay and clad carbon and low-alloy steels. The weld deposits harden very quickly by cold working. In addition, it is very easy to deposit a "crack-free" layer without a butter layer. The RTW filler metal fi nish on the MIG-spooled wire promotes smooth feeding through welding equipment and reduced tip wear in contact tips.