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Plasma Nitriding and Masking

We are looking for Plasma Nitriding of a Austenitic SS Hollow Bar of 1 M Long. We envisage by two step process i.e first Hard Chrome plating up to 100 microns with Hardness 1000 Hv. This is followed by Plasma Nitriding up to 60-80 microns. This has to be done at selective areas on the ID of the hollow bar. My question is how should we mask during hard chrome plating and also during nitriding. Is it a mechanical mask or chemical paste.

Also what is to be followed to ensure that nitriding occurs up to a depth of 60-80 microns.

Further information is required on the distortion/ deformation during nitriding as it involves high temperature.

Will be glad to responses at the earliest.

thanks in advance.

G.Saiprasad
- India.
2000

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What is the steady state and maximum parts temperature during ion-nitriding? How long is the temperature held at steady state?

Mandar Sunthankar
- Fort Collins, Colorado
2000

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2000

Dear Sir,

You can use either a copper based "stop off" paint to mask (from specified supplier) or use solid masking with mild steel rings, although this will be difficult practically as you are best treating the tubes vertically. You will have to stand the tube on spacers to allow the plasma to "escape" t the bottom or you will overheat and get gross distortion.

If you have an older cold wall furnace you will have to use very high pressures to get down the tube and maintain reasonable temperature uniformity - it will still be difficult. The fact that you are dealing with s/s helps as this is less sensitive to temperature of nitriding (within limits)

If you have pulsed plasma the job will be easier.

Best Regards
Richard

Richard Buster - Wolverhampton, United Kingdom

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Richard, Does Nitriding a mild steel affect the adhesion of a Nickel/Phosphorous deposit? Typically how deep does the nitrogen diffuse into the part after Nitriding? Thanks! Sincerely, Matt

Matthew Koerschner
- Oklahoma City, OK USA
2000

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Matthew, It is very difficult to answer you question precisely with regard to adhesion of deposits on Nitrided mild steel. If the nitriding parameters are well controlled you can suppress the formation of "compound or white layer" on mild steel and this is the product which can give you adhesion problems. Mild steel nitrides very rapidly as it has little or no alloy content to slow down Nitrogen migration (diffusion) through the steel. At say 500 Deg C you could obtain diffusion of Nitrogen up to 0.5 mm in 20 hours and perhaps 1 mm after 60 hours. The condition of the mild steel will also have a bearing.

Regards,

Richard Buster - Wolverhampton, United Kingdom
2000

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