Hydrogen Embrittlement


How to minimize the risk of internal hydrogen embrittlement of a screw?

Hydrogen embrittlement is neither visible nor predictable. Although manufacturing processes are optimized to minimize the risk of hydrogen embrittlement, there is no production method that can guarantee its complete elimination.

  • The standards for electroplated screws, ISO 4042 and ASTM F1941/F1941M, classify fasteners requiring a mandatory baking process as those having a minimum specified hardness above 390 HV. The baking process is specified by ISO 4042 at a temperature ranging from 190°C to 230°C for up to 24 hours (depending on the size, strength, and hardness of the screw). While this process will not completely eliminate internal hydrogen embrittlement, it greatly reduces the risk. (Fig 2.)

The electroplating process generates hydrogen, which can be absorbed by the screw. The objective of the baking process is to extract as much hydrogen as possible through effusion and trap the remaining hydrogen in the steel structure to immobilize it. This reduces the quantity of mobile hydrogen that causes hydrogen embrittlement.

  • For screws with a high risk of hydrogen embrittlement in applications with high mechanical requirements, it is recommended to use organic coatings in which no electrolysis process is conducted during the coating process.

 

How we can help to prevent hydrogen embrittlement in your assemblies

Hydrogen embrittlement failure happens unpredictably. Efforts to prevent it must be done during the design and manufacturing phase.

ChaenChia Application Engineers can help our customers to prevent hydrogen embrittlement failure in their assemblies by:

  • Recommending the material with less susceptibility to HE
  • Optimizing joint design to reduce tensile, shear and bending stresses
  • Selecting the most suitable coating for the screw that meets your corrosion requirements and reduces the risk of hydrogen embrittlement in your assemblies.

Many popular coatings like zinc plating (ASTMB633) create a barrier around the screw that does not allow hydrogen to easily diffuse out of the screw. More porous coatings will ensure greater hydrogen diffusion, minimizing embrittlement risks.