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Rusting of stainless steel grade 302 spring

Q. We are in the business of manufacturing stainless steel springs, grade 302. These springs are used in the rear view mirrors of automobiles. We have observed that during rainy season the springs get rusted and corroded. The material used in the manufacture of outer spring is SUS 302 grade and the material used to make the inner cable is also SUS 304 grade. The end fittings of the cable are made of brass material. We have not being able to find out what causes the rusting of the cable during rainy season. We will appreciate if you kindly advice us what to do to prevent corrosion.

Sanjay Saini
cables & automotive systems - Noida, U.P, India

First of two simultaneous responses --

A. The brass is causing galvanic corrosion of the (more anodic) stainless steel. Best to change the cable fitting material to stainless. If this cannot be done, see suggested solutions in MIL-STD-889 DISSIMILAR METALS. Chrome plating the brass fitting would greatly help. Paints that prevent direct contact of the dissimilar metals and waterproof sealants that keep the connection dry, e.g., synthetic rubber sealant conforming to MIL-S-8802F (now AMSS8802), can also be used.

Ken Vlach [deceased]
- Goleta, California

contributor of the year honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at, continue to benefit from.


Second of two simultaneous responses --

A. Have the springs been passivated? If not, then this is the reason they are corroding. Stainless steels are not impervious to corrosion, and require passivation treatments in order to maximize their corrosion resistance. Even with passivation, this grade can develop pitting in environments with high levels of chloride ions. You should obtain standards SAE J230 and ASTM A967 in order to understand the proper processing techniques.

Toby Padfield
Automotive module supplier - Michigan

A. Mr. Saini

All that needs to be said has been said and you should Nickel and Chrome plate the Brass fittings to reduce if not eliminate the Galvanic effects, and Definitely opt for passivating the 302 SS and the 304 SS parts .

The only aspect not considered is to switch to SS fittings totally, replace the Brass, if possible, and passivate all the SS parts for long life.

The solutions are domestically available.

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016


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