Nitriding Inconel 718

[Cherney]

Does anyone have experience with plasma nitriding inconel 718? I would lie to know if a nitrided layer of 10 microns can be achieved. Was also wondering what the processing time and temperature would be.
Thanks.

 

[EdStainless]

You would want to make sure that the temp aligns with the aging temp. I don't know if you can get enough diffusion at that temp as it is fairly low.
I have done some other Ni alloys and the penetration depths are low.

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P.E. Metallurgy, consulting work welcomed

 

[Cherney]

Thanks EdStainless. This is why I was wondering what the Nitriding temp was. 10 microns isn't much depth, but if the process temp to get there alters the tempering or if processing times are unrealistic,say 100 hrs or something, we may change course.

 

[EdStainless]

Which aging treatment are you using? You really should look into combining the two into one treatment, from a practical point of view.

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P.E. Metallurgy, consulting work welcomed

 

[Cherney]

Not possible for this application, and a tough one to write a spec for. AMS 2759/8 specifies that Plasma Nitriding must be carried out at a temperature not more than 50°C less than the tempering temp. Also, Nitriding times differ from thatof Aging. So, the two cannot be combined, at lest in this case anyway. I appreciate the creative idea though.

 

[mfgenggear]

what is the core hardness required?
what is the case depth required?
I have not had the pleasure but many other low alloy steels and precipitation stainless steels.
normally if core hardness is low enough heat treat first, then machine, then nitride. never done Inconel 718 ,
you may have to run test sample. and verify results

 

[EdStainless]

So how are you interpreting that temp requirement?
It was written with steels in mind.

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P.E. Metallurgy, consulting work welcomed

 

[Cherney]

EdStainless, you are correct in that 2759/8B is written for steel and does not refer to super alloys, such as Inconel 718. The specification is still a guideline for ion nitriding of aerospace parts, even if not 100% fitting for this material. There's little information available regarding my initial question on nitriding Inconel 718, so I came here in hopes of finding an answer. The parts will be aged 715°C for 16 hrs. Target core hardness will be 36-40HRC. My initial nitriding target temp is 560°C for 8 hrs (well within AMS2759/8B). If anyone has advice, experience or considerations for ion nitriding this material, I appreciate your response in advance.

 

[Cherney]

Mfgenggear: The total case depth required is 10-30µm

 

[EdStainless]

So not one of the traditional stepped aerospace aging treatment cycles.
Are you direct aging cold-worked material?
As I recall as long as you stay below 600C you are OK.
Getting a good clean, active surface will be the key to this working. getting the oxides off of this material can be tough.

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P.E. Metallurgy, consulting work welcomed

 

[Cherney]

EdStainless: Material will be HT somewhere around 1800°F, slow cooled prior to aging. Then machined and ion nitrided. Cleaning is not a problem. Where did you get information stating that going above 600°C would be detrimental? I had considered a higher temperature. What are the ill-effects?

 

[mfgenggear]

@Cherney
Plasma Nitriding 10-30µm should be no issues!
with plasma nitriding is normally all over
if it requires masking, (selective case depth) hard tooling is required, from my suppliers and experience.
case hardness will be up towards the 70 HRc
At this case depth no post grinding will be possible. parts will be finished.

I am sorry I can not tell you if Inconel 718 can be Nitrided, but take round test sample like the size of a tensile bar
and ask a supplier to run a test. then ask for a metlap of the case depth and hardness.

 

[Cherney]

mfgenggear: Thanks for the input. I am a little nervous that even 10µm will be a push. Trying to develop a general process spec to keep mfg cost in control. If, say 40 hrs nitriding is required, Yikes! I don't want a sudden surprise that blows the roof off cost. The more I can learn in advance, the better. Just wish there was more written material on the subject like there is with all other heat treatment.

 

[EdStainless]

from ATI:
Heat Treatment
The heat treatment consists of solution treating followed by a double aging treatment. Depending on the mechanical properties
desired, one of the following two heat treatments is utilized:
• For optimum impact properties:
Solution treat at 1,950° F (1,066° C) for 1 to 2 hours. Air cool.
Age at 1400° F (760° C) for 10 hours. Furnace cool to 1,200° F (649° C). Hold for total elapsed time of 20 hours. Air cool.
• For optimum tensile and creep-rupture properties:
Solution treat at 1,700-1,850° F (927 - 1,010° C) for 1 hour. Air cool.
Age at 1,325-1,400° F (718 - 760° C) for 8 hours. Furnace cool at 100° F (38° C) per hour to 1,150-1,200° F (621 - 649° C).
Hold 8 hours. Air cool.

Since the standard aging treatments require controlled cooling to 1150F(620C) I have always relied on subsequent heating below that level not changing the properties.
There is a different aging used for oil field applications and a different one yet for direct aging of cold worked material.

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P.E. Metallurgy, consulting work welcomed

 

[Cherney]

EdStainless: Ion Nitriding data is what I'm looking for.