face harden
/feɪs ˈhɑːrdən/
verb
- To treat the surface of a metal (such as steel) so that it becomes hard and resistant to wear, while the inside remains softer and tougher.
- The factory uses a special process to face-harden the gears for heavy machinery.
- This type of steel is often face-hardened for use in armor plating.
- Engineers face-harden the blade to make it last longer.