Salt Bath Nitriding of 420SS

[JohnNabors]

Does the salt bath nitriding process have any similar effect on the corrosion resistance of 420 as it does to austenitics? Are there any other deleterious effects?

Someone with our company sent out some 420 parts to be QPQ'd that had already been hardened to 45-50Rc. Need some quick answers. The parts in question are shaft sleeves for hydraulic driven submersible water pumps that will be continuously wetted on the wet side of a lip seal and most likely used to sump fresh water with lots of entrained sand in coastal areas where there is a fairly high chloride content.

Thanks for any help you can give -John

 

[arunmrao]

I have no answer regarding the corrosion aspect,but yes in paper industries we have given refiner discs made in 420 and then nitrided to good use.. Excepting that there is no sand in the paper pulp,other conditions are similar.

For pump shaft sleeves you can try 17-4 SS and the bore can have a ceramic coating. This gives a very good performance.

 

[swall]

Salt bath nitriding will destroy the corrosion resistance of 420 stainless. We used to flash chrome plate any 410 stainless that we nitrided in order to try to establish a passive layer. This was all anecdotal from our chemists and don't what, if any testing had ever been performed. QPQ type nitriding may be a different story--I think Unclesyd may have had some experience with QPQ on martensitic stainless.

 

[mcguire]

The nitrogen wil form chromium nitrides so the stainless will no longer be stainless without chromium in solution to form a passive film.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[unclesyd]

I've never used 420 SS in a wearing service where corrosion resistence was also needed as we would switch to 440C for the added corrosion resistence. I did LNC some 410 SS and got very mixed results that were very dependent on the corrosive media. My best results were obtained using LNC 17/4 PH SS for pump components.

Take a look at the brochures at this site.

http://www.nitromet.com/A55B6F/nitr...2f63208410852571930048a8da/TechnicalResources

 

[EdStainless]

Hit and miss will be the best that you can hope for.
420 does not have great corrosion resistance to start with and nitriding will make it worse.
I wouldn't count on this. You need to move to a better alloy.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[JohnNabors]

All of this agrees with what I suspected. Thanks for providing some second opinions I can use to beat up Purchasing with.

 

[rmw]

Ahhhhh....., Purchasing. The engineering genuis's that they are.

rmw

 

[macmil]

There are speciality manufacturers of shaft sleeves who will provide custom sleeves for your application. Disclosure~ I represent one. Generally for the most severe service the abrasion resistant surface is a coating, sometimes specially formulated, applied to the base steel either carbon or stainless, with a strong bond to prevent delamination.