Rust Proof and chemical resistant coating for steels

[ChristopherTurner]

I have a mechanical assembly that will be attached to the head of a numerous engine types as a research and development tool. Unlike most assemblies on an engine head, this assembly is totally sealed and will not be exposed (externally)to engine oil. As a result, the system will rust. I need a coating that can be applied that will not allow rust to form.
During development the system will potentially be exposed to the following:
-Humid sealevel ambient conditions (including salt in the atmosphere)
-Engine oil (during assembly and dis-assembly
-Deisel Fuel
-Gasoline
-Solvents such as methanol (used to clean the parts)
-Carburator Cleaner
The materials I need to coat are - 4140 with a carbonitride coating and Grade 12.9 4037.

Does anyone have a suggestion of a coating I can use? This coating can be a "line-of-sight" type coating or chemical dip type coating (or any other type really). Please keep in mind I would like to apply this coating after heat treat so the coating process should not include heat exposure above the tempering temperature of the materials (400-450°C)

Thanks,
Chris Turner
719-686-6061
Sturman Industries
cturner@sturmanindustries.com
or cturner77@comcast.net

 

[IRstuff]

What about chrome? It'll look nice, as well.

TTFN

 

[ChristopherTurner]

I would look at chrome, however probably as a last resort. There are numerous internal features (including match fits for hydraulic actuators that are ~0.004 - 0.006mm diametral and other bearing surfaces) that would need to be masked so that the chrome plating would not occur in these areas. I have also been warned by some metallurgists that hydrogen imbrittlement may occur. Thanks for the suggestion and I will keep it in mind. Also, do you (or anyone) know of some techniques used to mask parts that are to be chromed.

Chris Turner

 

[CoryPad]

Hydrogen embrittlement is a definite concern with electroplated chromium.

How about electrocoating? It will provide corrosino resistance in your conditions, but may be somewhat costly for a single piece.

Actually, a good epoxy-based paint ought to work also.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ChristopherTurner]

Can anyone comment on using a CrN coating on top of an electrolys Nickel coating. I have heard that this may work well.

 

[CoryPad]

CrN over electroless Ni is complete overkill for your application. Those coatings are for wear resistance, not for appearance maintenance.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[JTreglio]

If you really want a good corrosion resistant coating, consider IVD aluminum. It's used extensively by the military as a replacement for cadmium plating. It was developed many years ago at McDonnell-Douglas in St. Louis (now Boeing).

Jim Treglio
Molecular Metallurgy, Inc.

 

[swall]

I like electroless nickel for the 12.9 fastener. For the 4140 part, if it is to be carbonitrided, you could consider one of the black salt bath nitride coatings, such as QPQ. Unless of course the 4140 part is already made and carbonitrided, then I would just go with the electroless nickel for that as well.