Protective Coating for 4140 Steel Shaft

[oharag]

Hello. I was wondering what type of coating is recommended for Alloy Steel 4140. We are currently using this for a bearing shaft. The tolerances are in the tenths so controlling thickness is critical after application of the coating. Is there anything out there that can coat this material without adding thickness? Or do I have to add a note: "Final dimensions are considered after applying coating.", and let the machine shop account for coating thickness?

I guess we could consider a stainless steel shaft so that corrosion is not a concern. Any thoughts on which type to use for a bearing shaft?

Sorry for my ignorance. Coatings have never been my thing. I know I should get more comfortable with the many options out there. Any links to good sites offering advice on the subject?

Thanks,
oharag

 

[JimMetalsCeramics]

YOU COAT WITHOUT ADDING THICKNESS BY PERFORMING A CONVERSION COATING. HEAT TREAT THE PART IN A CARBURIZING OR NITRIDING FURNACE. YOU ALSO HAVE THE OPTION OF 'PLASMA" NITRIDING. THESE PROCESSES WILL HARDEN THE SURFACE OF THE STEEL.

 

[MaterialsEngineer]

Oharag,

You might want to investigate a vacuum deposited thin film coating like DLC (Diamond Like Carbon).

There are companies such as Diamonex and Balzers who are well known industry sources for this type of coating.

Good luck.

 

[TridentSC]

"Coating" is a pretty broad term. Conversion coatings like nitriding, anodizing, etc. change surface characteristics without changing dimensions. Thermal spray, Plasma Transferred Arc, laser cladding and others add a layer of different material to the substrate, changing the geometry as well as the surface characteristics in the process.

If you need hardness for wear resistance either conversion or one of the other processes can help. If you need corrosion resistance, or a combination of the two, an overlay process would probably be better.

sulzermetco.com offers a good overview of the thermal spray world.

 

[PEMechE]

First determine if you need a coating. If the shaft is in a dry/lubricated environment, you may not need a coating or plating.

You may want to provide more details on your application to obtain better advice.

For reference..
I typically use electroless nickel plating if it is a shaft supported by bushings in journal bearing type arrangement. Nickel holds up well in a journal bearing type application.
If I am using live element bearings such as roller bearings, thurst bearigs etc, and I need corrosion resistance, I use zinc plating.
The machine shop can adjust the before plating dimensions to achive your final allowance. Make sure and embrittlement releif treatment is used in the plating process if your shaft is approx. harder than Rc35. You may want to use the ASTM specification for nickel plating, it is very detailed.