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.
ASTM – A967 Specification
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)…
• AMS-QQ-P-35 (Replaced QQ-P-35)
• AMS 2700
• ASTM A-380
• ASTM A-967
• ASTM F-86 (Titanium Components)
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.
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.
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.