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Passivation
Passivation remains a critical step in maximizing the essential corrosion resistance of parts and components machined from stainless steels. It can make the difference between satisfactory performance and premature failure. Incorrectly performed, passivation can actually induce corrosion.
Passivation is a post-fabrication method of maximizing the inherent corrosion resistance of the stainless alloy from which the workpiece was produced. It is not a scale removal treatment, nor is it like a coat of paint.
Passivation is a process that uses an acid (nitric or citric acid) solution to remove the surface iron and other contaminants that cause corrosion in the Stainless Steel. Prior to an entering the acid the parts are cleaned to remove any oil and organics. Through the entire process an almost immeasurable amount of material is removed and leaves the chrome on the surface which oxidizes creating a very thin (less than .000001”thick) passive chrome oxide layer.
Advantages of passivation:
- Improved Corrosion Resistance
- Uniform, Smooth Appearance and Finish
- Deburring (Polished Surface)
- Cleanliness
- Improved and Extended Life of Product
300 Series |
400 Series |
ASTM – A967 Specification |
| Citric Acid |
- Removes free iron from the SS substrate…
- Achieves a passive surface…
- Meets QQP-35C (replaced by ASTM A967 [AMS-QQ-P-35])…
- Tested and approved by the aerospace, medical, machining/manufacturing, & food industries…
- Brightens 300 series SS alloys…
- Excellent appearance on 400 series SS…
- Operates at a higher pH…
- 3.0-3.2 for 400 series SS
- 4.5-5.0 for 300 series SS
- Lower metal removal rate
- 0.0010 mills/minut per surface (performed on 303 SS)
- Accepted as an alternative to nitric acid/sodium dichromate for AMS-QQ-P-35 Type II on 303 SS (less chance for pitting)
Medical Passivate |
Military Specification |
| Nitric Acid |
Removes free iron from the SS substrate…
•Achieves a passive surface…
•Meets QQP-35C (replaced by ASTM A967 [AMS-QQ-P-35])…
•Tested and approved by the aerospace, medical, machining/manufacturing & food industries…
•Brightens 300 series SS alloys…
•Not as bright of an appearance on 400 series SS…
•Low operating pH…•<3.0 for all series of SS
•Higher metal removal rate 0.0028 mills/minute per surface (performed on 303 SS)…
Specifications
• AMS-QQ-P-35 (Replaced QQ-P-35)
• AMS 2700
• ASTM A-380
• ASTM A-967
• ASTM F-86 (Titanium Components)
QQ-P-35C |
| Testing |
Water Immersion
Verifies the passivation process on all grades of stainless steel, with exception of 440C. After testing, specimens shall show no signs of rust or corrosion.
Copper Sulfate
Verifies the passivation of austenitic stainless steel in the 200 and 300 series conducted in accordance with MIL-STD-753 Method 102. The specimens shall show no signs of copper deposit.
Salt Spray
Performed in accordance with ASTM B117 for 2 hours, when specified by engineering drawings. After testing, specimens shall show no signs of rust, stain or corrosion.
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