Would you like details on baking parameters for specific fastener grades?

To ensure effective hydrogen embrittlement relief (HER), the baking time and temperature must be optimized based on: Fastener material strength (e.g., Grade 5 vs. Grade 8) Plating type (e.g., zinc, cadmium, chrome) Industry standards (e.g., ASTM, ISO, MIL-SPEC)

 

Hydrogen Baking Parameters for Different Fastener Grades

To ensure effective hydrogen embrittlement relief (HER), the baking time and temperature must be optimized based on:

• Fastener material strength (e.g., Grade 5 vs. Grade 8)

• Plating type (e.g., zinc, cadmium, chrome)

• Industry standards (e.g., ASTM, ISO, MIL-SPEC)

Here’s a detailed breakdown:

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1. General Baking Guidelines

• Temperature Range: 190–230°C (375–450°F)

  • Lower temps (~190°C): Used for high-alloy steels to avoid tempering effects.

  • Higher temps (~230°C): For carbon steels; accelerates hydrogen diffusion.

• Time: 4–24 hours (depends on fastener strength and hydrogen absorption risk).

• Critical Window: Baking must begin within 1–4 hours after plating to prevent hydrogen migration.

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2. Baking by Fastener Grade/Class

Fastener Grade	Tensile Strength	Recommended Baking	Notes
Grade 2 (ASTM A307)	≤60 ksi (414 MPa)	Not required	Low-strength; minimal embrittlement risk.
Grade 5 (ASTM A449)	120 ksi (827 MPa)	8–12 hrs @ 200°C (390°F)	Common for automotive; moderate risk.
Grade 8 (ASTM A354)	150 ksi (1,034 MPa)	18–24 hrs @ 200–220°C (390–430°F)	High-risk; aerospace/military often require 24 hrs.
Class 10.9 (ISO)	1,040 MPa	18–24 hrs @ 220°C (430°F)	Common in EU/Asian automotive.
Class 12.9 (ISO)	1,220 MPa	24 hrs @ 200°C (390°F) max	Avoid >200°C to prevent tempering.
ASTM A490 (Structural Bolts)	150–173 ksi	24 hrs @ 220°C (430°F)	Bridges/buildings; strict baking required.

Note: For electroplated cadmium (MIL-STD-1500), baking times may extend to 48 hours for critical aerospace fasteners.

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3. Baking by Plating Type

Different platings introduce varying hydrogen levels:

• Zinc Electroplating (Most Common):

  • High hydrogen risk – Requires full baking (e.g., 24 hrs for Grade 8).

• Cadmium Plating (Aerospace):

  • Very high hydrogen absorption – Often baked for 24–48 hrs.

• Mechanical Zinc (Zinc Flake, e.g., Geomet):

  • No baking needed – Non-electrolytic process avoids hydrogen.

• Trivalent Chromium:

  • Lower hydrogen than hexavalent chrome but may still require 8–12 hrs baking.

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4. Industry-Specific Requirements

• Aerospace (AMS 2759, NADCAP):

  • Mandatory 24-hour bake for high-strength fasteners (≥180 ksi).

  • Oven calibration and temperature uniformity (±5°C) strictly enforced.

• Automotive (SAE J2339):

  • 8–12 hrs for Grade 5/8.8 fasteners.

• Military (MIL-STD-1312):

  • Bake within 1 hour post-plating for critical applications.

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5. Exceptions & Alternatives

• Stainless Steel (A286, 17-4PH):

  • Baking not typically required (low hydrogen diffusion).

• Coated Fasteners (Dacromet, Magni):

  • No baking needed (applied via non-electrolytic methods).

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6. How to Verify Effectiveness

• Delayed Failure Testing (ASTM F519): Fasteners are loaded to 75–90% of yield and held for 200+ hours to check for cracks.

• Hydrogen Analysis: Thermal desorption spectroscopy (TDS) for residual hydrogen measurement (used in R&D).

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Key Takeaway

For high-strength steel fasteners (≥Grade 5/8.8):

1. Bake at 200–220°C for 18–24 hours.

2. Start within 1–4 hours after plating.

3. Follow ASTM/ISO/MIL standards for critical applications.