Nital Etch Inspection

Nital etch inspection identifies whether heat has been introduced into a tempered steel component by operations such as machining, pressing, or grinding. Grinding generates extreme frictional heat that can alter the metallurgical structure of the affected area. After etching, altered areas show as light gray to white areas with a light brown to black border, or as light brown to black indications darker than the surrounding material. CMP uses a 3–5% nitric acid solution in water and a 4–6% hydrochloric acid solution in water.