Hydrogen Embrittlement Relief AMS 2759
Thermal stress relief or baking for Hydrogen embrittlement is a process after plating to remove the hydrogen infused during the cleaning and plating process. Hydrogen embrittlement can also be formed in the metal during the casting and forging process. The hydrogen gas bubbles form in the granular structure of the metal and causes embrittleness and premature failure of the part.
The process is typically done to fasteners, springs, and other metal parts having Rockwell C (R) Hardness of 30 or higher. This process must be done within 1 hour of the plating process. Baking for Hydrogen Embrittlement relief is done at a controlled temperature of 375 D.F plus or minus 25 D.F. for a minimum of three hours. Most hydrogen is removed within the first three hours, however, some harder materials require a baking time of up to 23 hours.
If the hydrogen is not removed after the plating process, it will cause failures in the material. The failures for which we are concerned are a result of very small quantities of hydrogen. Traditional ductility test may not detect this condition. The hydrogen embrittlement occurs on an atomic level when the hydrogen atoms concentrate in a certain areas of the metal causing instability in the material. The concentrating hydrogen atoms cause an internal stress crack. These stress cracks are what lead to eventual failures in the material.
It is very important for you, the manufacturer, to know your metal. What are the hardness or strength levels and what processes have been performed on it before, during and after your manufacturing process? What are any unusual characteristics about your part? This is critical information that the plater needs to know prior to plating and should be relayed in writing either on the purchase order or on the print. Please contact Seminole Metal Finishing or your heat treater for any other questions on this very important subject.