Etch Inspection of High Strength Steel Parts
|Publication Date:||1 December 2013|
This specification establishes the requirements for etch inspection of steel parts to detect overheating (rehardening or overtempering) caused by abusive machining or grinding, or to detect localized discontinuous carburization.
This process has been used typically for carburized parts and for bare low-alloy steel parts having tensile strength of 180 ksi (1241 MPa) and higher, but usage is not limited to those applications. The process can also be used to detect abusive grinding or machining in heat treatable steels of lower core hardness. This process may remove 0.0001 to 0.0005 inch (2.5 to 12.7 micrometers) from the surface of the part.
Etchants used in this specification are classified as follows:
Type 1 - Nitric acid in water or alcohol with an anti-smut additive
Type 2 - Nitric acid in water or alcohol
Type 3 - Ammonium persulfate in water
Type 1 and Type 2 etchants may be used interchangeably. Type 1 immersion or Type 3 swabbing method shall be used when the part cannot be hydrogen embrittlement relieved.
Type 3 etchant shall be applied by swabbing and only used when authorized by the cognizant engineering organization. Type 3 is not as sensitive for detecting grinding burns as Type 1 or Type 2.
Safety - Hazardous Materials
While the materials, methods, applications, and processes described or referenced in this specification may involve the use of hazardous materials, this specification does not address the hazards that may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and to take necessary precautionary measures to ensure the health and safety of all personnel involved.