Most common and effective method for high-strength fasteners. Process: Heating fasteners at 190–230°C (375–450°F) for 4–24 hours (depends on material strength and plating type). Key Considerations:
Author: Robby
Dehydrogenation (hydrogen removal) of fasteners after plating is crucial to prevent hydrogen embrittlement, especially for high-strength steel fasteners (e.g., Grade 8, 10.9, 12.9). There are several methods to remove hydrogen, each with its own advantages and limitations. Here are the primary techniques:
1. Baking (Thermal Hydrogen Embrittlement Relief)
Most common and effective method for high-strength fasteners.
Process: Heating fasteners at 190–230°C (375–450°F) for 4–24 hours (depends on material strength and plating type).
Key Considerations:
Must be performed within 1–4 hours after plating to prevent hydrogen diffusion deeper into the metal.
Oven temperature uniformity is critical (per AMS 2750 for aerospace applications).
Standards: ASTM B850, ISO 9587, MIL-STD-1312, AMS 2759.
2. Room Temperature Aging (Natural Dehydrogenation)
Process: Letting fasteners sit at ambient temperature for 48–72 hours to allow hydrogen to diffuse out naturally.
Pros: No energy cost; suitable for low-risk applications.
Cons:
Much slower than baking.
Less reliable for critical high-strength fasteners.
Used for: Low-to-medium strength fasteners or non-critical applications.
3. Mechanical Vibration (Stress-Assisted Hydrogen Diffusion)
Process: Subjecting fasteners to controlled vibrations or ultrasonic energy to help dislodge hydrogen.
Pros: Faster than room temperature aging.
Cons:
Less proven effectiveness compared to baking.
Not widely accepted in high-reliability industries (aerospace, automotive).
Used for: Experimental or secondary treatment in non-critical applications.
4. Electrochemical Dehydrogenation (Reverse Plating)
Process: Applying a low-current reverse electrochemical treatment to drive hydrogen out.
Pros: Can be faster than baking in some cases.
Cons:
Risk of over-etching or damaging the plating.
Requires precise control.
Rarely used in industrial fastener production.
5. Alternative Plating Processes (Minimizing Hydrogen Intake)
Mechanical Plating (Peen Plating):
No electrolytic hydrogen generation (e.g., mechanical zinc plating).
Does not typically require dehydrogenation.
Trivalent Chromium Plating:
Generates less hydrogen than hexavalent chrome.
May still require baking for high-strength fasteners.
6. Testing for Residual Hydrogen (Verification Methods)
Delayed Failure Testing (ASTM F1940): Fasteners are subjected to sustained load to check for hydrogen-induced cracking.
Hydrogen Permeation Tests: Electrochemical methods to measure remaining hydrogen.
Bend Tests: Qualitative checks for embrittlement.
Which Method is Best?
Method Best For Limitations
Baking High-strength, critical fasteners Requires oven, time-consuming
Room Temperature Aging Low-risk, low-strength fasteners Slow, unreliable for high-strength
Mechanical Vibration Experimental/non-critical cases Limited validation
Electrochemical Rare, specialized cases Risk of damage
Conclusion
Baking is the gold standard for high-strength plated fasteners (e.g., aerospace, automotive).
Room temperature aging may suffice for low-strength or non-critical parts.
Mechanical/peen plating avoids hydrogen issues altogether but has limited corrosion resistance compared to electroplating.
For critical applications, baking within 1–4 hours post-plating is mandatory per industry standards. Would you like details on baking parameters for specific fastener grades?