What is Hydrogen Embrittlement and is there a Test for Hydrogen Embrittlement for Socket Set Screws?
Hydrogen embrittlement is a metal’s loss of ductility and reduction of load bearing capability due to the absorption of hydrogen atoms or molecules by the metal. The result of hydrogen embrittlement is that components crack and fracture at stresses less than the yield strength of the metal.
Causes leading to hydrogen absorption
Hydrogen can enter and diffuse through steel even at room temperature. This can occur during various manufacturing and assembly operations or operational use – anywhere that the metal comes into contact with atomic or molecular hydrogen.
In our standard process for which there is a possibility of absorption of hydrogen is electroplating. During electroplating, hydrogen is produced at the surface of the metal being coated. Electroplating is used to deposit zinc or cadmium on the socket set screws for corrosion protection of the steel.
Hydrogen absorption can also occur when a socket set screw is in service if the steel is exposed to acids or if corrosion of the steel occurs.
Requirements for failure due to hydrogen embrittlement
There are three requirements for failure due to hydrogen embrittlement:
- A susceptible material.
- Exposure to an environment that contains hydrogen.
- The presence of tensile stress on the component.
High-strength steels with a hardness of R/C 32 or greater are the alloys most vulnerable to hydrogen embrittlement. Although electroplated socket set screws in alloy steel fall in that category, they are designed to be used in a compression application deeming tensile stress absent, thereby making socket set screws an exception to the rule (Reference ASTM F912-11 (Reapproved 2025). Reference paragraph 1.2. It reads: These set screws are intended for compression applications only and are not customarily subjected to embrittlement tests. For tensile applications, consult with the manufacture for proper alloy and hardness.
Prevention of hydrogen embrittlement
Baking socket set screws after electroplating at 375° +/- 25°F within 3 hours after the electroplating process per ASTM B 850 for a period of 23 hours to allow the hydrogen to diffuse out of the metal.
Finally, there is no test for hydrogen embrittlement on socket set screws. Nowhere in ASTM-F912 is it required to be done, regardless of finish. Socket set screws that load in a tensile application is in contradiction with ASTM-F912. Socket set screws with a standard hardness of R/C 45-53 are intended for compression applications only. There are no parameters in QQ-P-416 to perform hydrogen embrittlement testing on socket set screws.