Zinc and 300 series combination

[johnnymist2003]

Hi all,

I'm not a corrosion engineer, so forgive me if the terminology I use is incorrect. I have a 304 stainless steel stud bar passing through a hole in a galvanised carbon steel plate. I have been advised that to mix 304 ss and galvanised materials is not recommended as the zinc interacts with the chrome in the stainless steel, reducing the strength of the stainless steel. The application is in an air cooled heat exchanger, holding the motor adjusting plate to the bridge frame, the temperature probably will not exceed 40 deg celsius. The top stud bar is under tensile loading and the bottom ones under compressive loading, due to the vertival mounting arrangement. Please supply any advice. Thanks.

 

[TVP]

What is the rest of the environment (chemicals, cyclic exposure to water, etc.)? In general, the more active metals (the zinc and carbon steel) will be corroded vs. the more passive metal (stainless steel).

 

[EdStainless]

As long as you don't weld the only problem that you will see is somewhat accelerated corrosion of hte galvanized steel parts.

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[kenvlach]

Zinc embrittlement of austenitic stainless steels occurs slowly at 419-570 [sup]o[/sup]C, and more rapidly at higher temperatures, becoming extremely fast with crack propagation above 750 [sup]o[/sup]C. From

ASM Handbook Vol. 13A, Corrosion: Fundamental, Testing, and Protection p. 390-391 (2003).

Welding and fires can cause catastrophes. SS is preferably passivated after any contact with zinc.

 

[FinishingTalkdotcom]

Ionic Zinc reacts with ionic chromium (in its hexavalent state) in an acidic catalyzed solution to form zinc chromate. I would not think this reaction should occur in their uncharged state as metal. The only reaction I would expect is the zinc corroding, which is why zinc is sometimes referred to as a sacrifical coating.