Stopping-off

Masking an area of a component to prevent case hardening or surface contamination during heat treatment.

Areas of components that must not be case hardened can have a special coating applied to prevent the controlled atmosphere from contacting the surface. Thus, no carbon or nitrogen is absorbed in those areas, which remain soft.

Stopping-off is usually carried out in either of two ways:
Plating the area to remain soft with copper (Cu), to a depth of 20µm to 25µm.
Painting the area to remain soft with a proprietary stopping-off paint.