Passivation of Stainless Steel Components under ASTM A967 Citric Acid Protocols
Engineering Overview: Chemical process guide on citric acid passivation for stainless steel pins, cams, and springs, maximizing chromium oxide passive layer formation.
Technical & Engineering Specifications
| Corrosion Test | ASTM A380 High-Humidity Water Immersion Test |
|---|---|
| Standard Reference | ASTM A967 / AMS 2700 Citric Acid Passivation |
| Temperature & Time | 55°C for 20 Minutes Immersion |
| Chemical Concentration | 4% to 10% Citric Acid Solution (pH 1.8 - 2.2) |
Chemical Passivation Science
Machining stainless steel lock components (SUS304/SUS316 pins, springs, bridges) leaves free iron particles that cause surface rust spots. ASTM A967 Citric Acid Passivation chemically removes exogenous iron.
Chromium Oxide Barrier Formation
- Citric Acid Bath: 4%–10% organic citric acid at 50°C–65°C selectively dissolves free iron without depleting chromium.
- Passive Layer: Promotes a continuous, ultra-dense Chromium Oxide passive film (>= 2.5 nm) that self-heals in atmospheric oxygen, boosting salt spray life by 300%.
Frequently Asked Engineering & Selection Questions
Q1: Why is citric acid passivation preferred for lock parts?
It cleanly dissolves free iron contamination while being non-toxic, maximizing the natural chromium oxide rust-defense barrier.