Solution of about 2 to 5 percent nitric acid in ethanol or methanol, the default etchant for carbon and alloy steel metallography. On polished mounts it darkens martensite and pearlite, outlines ferrite grains and shows decarburized layers. Applied to ground surfaces of hardened parts as a temper etch inspection, it shows grinding burn as dark retempered or light rehardened patches.
Bearing journals failed nital etch, dark bands all the way around the ground diameter.
Also heard as
- nital
- temper etch
- etch inspection
Related terms
Cut and etch
Shop phrase for sectioning a sample part and etching it to check case depth or structure.
Grinding burn
Heat damage to a hardened surface from abusive grinding, which softens it or creates brittle rehardened spots.
Decarburization
Loss of carbon from the surface of steel during heating, leaving a soft skin that will not fully harden.