Nitriding

Teach me about it.

We are currently using ion nitriding on Inconel 901. We are experiencing oxidation formations in high temperature (~1000 F) environments. One thought is that any oxygen in the gas supply of the nitriding can cause microcracks in the nitrided layer which allow formations to begin.

Teach me about nitriding. My understanding is that salt bath nitriding is better, but super environmentally unfriendly. It is also that the purity of the anhydrous ammonia can differ from 99.5%-99.8% (agricultural), 99.5%-99.8% (commercial) and 99.995% (metallurgical). Will those purities make a noticeable difference in the amount of oxygen present?

tuna55 wrote: My understanding is that salt bath nitriding is better, but super environmentally unfriendly.

Sounds like a job for...China! With super-polluting powers!

I was trying to come up with some visual pun centered around David Hasselhoff and ghost riding the whip. It didn't work.

I'm interested in this discussion, but have nothing to offer.

GameboyRMH wrote:

tuna55 wrote: My understanding is that salt bath nitriding is better, but super environmentally unfriendly.

Sounds like a job for...China! With super-polluting powers!

Yeah, apparently it involves dissolving cyanide salts...

In the '70s, there was an alternative process to nitriding call tuftriding. Whatever happened to that? Also, what's up with nitrided cranks sometimes bending during the process?

Tuffriding is what's done in England I think.

I researched this a while back, but have forgotten most of it.

Duke wrote: I was trying to come up with some visual pun centered around David Hasselhoff and ghost riding the whip. It didn't work.

Sounds like a job for...Google!

A good link. answered most of my questions:

http://www.crankshaftco.com/steel-crankshaft-hardening.html

I noticed that article, which is the one I read before, indicated nitriding was for steel cranks. Cast iron cranks don't need to be nitride (or tuffrided).

spitfirebill wrote: I noticed that article, which is the one I read before, indicated nitriding was for steel cranks. Cast iron cranks don't need to be nitride (or tuffrided).

Yes, the article states cast iron becomes work-hardened during the machining process.

I can ask my old man he is a metallurgist and might have some information for you. Good luck with it.

My old man will look into it further but he said it sounds like the environment either contains oxygen or moisture. You might need to vacuum purge the vessel with dry nitrogen while it comes to temperature. That's the first guess. Sounds almost like smelting titanium where it is very sensitive to environment. Good luck!

benzbaronDaryn wrote: My old man will look into it further but he said it sounds like the environment either contains oxygen or moisture. You might need to vacuum purge the vessel with dry nitrogen while it comes to temperature. That's the first guess. Sounds almost like smelting titanium where it is very sensitive to environment. Good luck!

He's on the money. We expect oxygen. The question is, is that what the content of the impurities in the supply gas are? Is that easily controlled?

tuna55 wrote: Teach me about it. We are currently using ion nitriding on Inconel 901. We are experiencing oxidation formations in high temperature (~1000 F) environments. One thought is that any oxygen in the gas supply of the nitriding can cause microcracks in the nitrided layer which allow formations to begin.

Not that I can help out much, but I was not clear on the wording.

Are you experiencing oxidation problems during the nitride process that is resulting in observable micro-cracks and oxidation deposits on the finished part or are you subsequently experiencing oxidation on the part when it is put into use in a 1000 degree environment? I ask because the nitride process is done around 1000 degrees and Inconel is a material often used in high heat tight tolerance applications.

If it is a nitride process problem can I ask how you are cleaning the parts? In as much as you want pure amonia, contaminants can also come in on the part itself. Plasma cleaning is often the only way we can get some of our parts clean enough for processing. It has the added benefit of surface activation.

The other variable is the chamber itself. Extrapolating from some of the ion etching and vapor deposition chambers that we use, if the chamber is contaminated it will not give optimal results. Might want to try another supplier (Unless you ARE the supplier)

So, we are experiencing microcracks and gran removal after 40,000 hours in this environment. We're not talking infant mortality. We're wondering if there is anything we can do from a process perspective to improve this.

I am thinking the answer is "no", but we are not sure.

So every 4.5 years the part wears out. Cause of failure is oxide observe in/under or near micro/cracks. Part works in 1000 degree environment.

How long you want to last? Maybe coat it with Viagara!

NOHOME wrote: So every 4.5 years the part wears out. Cause of failure is oxide observe in/under or near micro/cracks. Part works in 1000 degree environment. How long you want to last? Maybe coat it with Viagara!

10 years

The fun thing about these projects is that it takes a looooonnnngggg time before you know if your change made a difference.

How DO you prep the parts before treatment to be 100% certain that they don't bring any contaminants into the process?

Sounds like you're getting oxidation or water contamination. Do you have the ability to add powdered coal or metal that won't alloy with the Inconel into the process as an oxygen getter?