Growth due to Plasma Nitriding

[FennLane]

I am planning to make a small batch of close tolerance shafts from a 4340 VAR steel.

The shafts will need significant machining on their ends and we plan to stress relieve at 630degC prior to grinding.

Once ground we would like to Plasma Nitride the shafts (400 degC) and use them without further work.

The case depth we will need is very shallow but we need a shaft tolerance of 17.992 to 18.000mm.

The company that carries out the Plasma Nitriding say that I will not need a 'process grinding allowance' but I am not 100% confident.

I have limited experience of plasma Nitriding and I am not sure how much growth, if any, will occur.

Any information about typical growth would be very helpful.

 

[EdStainless]

At that close tol I think that you will see some growth. But that said, since this is low temp and shallow you should be able to manage it.
If it were me I would grind in the bottom half of the tol and let it go.

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P.E. Metallurgy, Plymouth Tube

 

[CoryPad]

The growth after nitriding is typically around 2.5 micrometers per surface or 5 micrometers for a diameter.

 

[tbuelna]

Besides dimensional change, another concern with your close tolerance surfaces after nitriding is presence of any white layer. Conventional gas nitriding leaves a thin, brittle white layer that is typically removed by grit blast, chem etch, polishing, etc. However, with the plasma nitriding you are using I believe the white layer can largely be eliminated with careful control of the process. So you might want to discuss this with your plasma nitriding vendor.