What is the primary cause of hydrogen embrittlement in carbon steel wave springs, and what specific post-treatment protocols prevent this catastrophic failure?

Hydrogen embrittlement occurs when atomic hydrogen penetrates the carbon steel crystal lattice (typically high-carbon spring steels such as SAE 1070-1090) during electroplating, acid pickling, or in highly corrosive operating environments.

Mechanism:
Hydrogen atoms diffuse and accumulate in areas of high tensile stress, micro-voids, or dislocations. When the spring is loaded under stress, these atomic pockets recombine into hydrogen gas molecules ($H_2$), generating high internal gas pressure that initiates micro-cracking and leads to immediate, brittle, catastrophic structural failure under low design loads.

Mitigation and Preventive Protocol:
1. Avoid Acid Cleaning: Use mechanical descaling or alkaline cleaning instead of hydrochloric or sulfuric acid baths.
2. Relief Baking (Mandatory): Within 1 hour (maximum 4 hours) of electroplating (e.g., zinc or cadmium), the wave springs must undergo stress-relief baking at $375^\circ F \text{ to } 400^\circ F$ ($190^\circ C \text{ to } 205^\circ C$) for a minimum of 4 to 24 hours (refer to ASTM F1940 / ASTM B850).
3. Baking Window: Delayed baking after electroplating allows the hydrogen to permanently localize, rendering baking ineffective.