ISO 14104:2017 specifies procedures and requirements for the detection and classification of localized overheating on ground surfaces by chemical etch methods.
The process described in this document is typically used on ground surfaces; however, it is also useful for the detection of surface anomalies that result from post-heat treatment machining such as hard turning, milling and edge breaking (deburring) processes. Surface metallurgical anomalies caused by carburization or decarburization are also readily detectable with this process.
Some methods which have been used in the past are no longer recommended. Specifications are intended to be changed to use the methods in this document. These etching methods are more sensitive to changes in surface hardness than most hardness testing methods.
ISO 14104:2017 applies to steel parts such as gears, shafts, splines and bearings. It is not applicable to nitrided parts and stainless steels.
NOTE This process, although at times called "nital etch", is not intended to be confused with other processes also known as "nital etch".
The surface temper etch procedure is performed after grinding and before additional finishing operations such as superfinishing, shot peening and honing.