Galling question about 718 inconel and 17-4 1025 or h1075 1

[aroundhere]

We changed all of our housings for a set of tools from 4340 to 718 Inconel. The people that made the changes didnt even consider the parts the new inconel housings will be screwing together with and if we will have galling. We normally copper plate/armoloy coat the threads and oring grooves when screwing a 17-4 part with another 17-4 part. I havent worked with enough Inconel to know if galling the threads are going to be a major concern when screwing together with a 17-4 (usually H-1025) part. I dont have the spec in front of me for the inconel718, but the yield strength is approx 125ksi. The Rc hardnesses are probably fairly similar to the 17-4 (maybe high 30s-low 40s. Everyone has been screwing the inconel and 17-4 parts together so far, but I am concerned with long term issues. I would guess that I will need to plate the threads on the male 17-4 h-1025 parts, but was hoping I would get some feedback on the subject also. The next question may need to be in the plating/coating section.....has anyone ever tried or had issues with fluid leakage when plating the oring grooves (or entire part) with armoloy? We have been doing this for a few years and never had any issues, but was curious if anyone else did this. The beauty of Armoloy is that it is so thin you dont have to machine your threads/oring outer diameters to the low side before coating like is needed when copper plating. Our typical pressures are 20,000 psi @400degF. Any and all comments are welcome.

 

[EdStainless]

Your 718 should be aged and have a min yield of 150ksi, min UTS of 180ksi.
Armoloy wouldn't hurt, but I doubt that you need it.
Mating 718 with 17-4 does not cause me any concerns.

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Plymouth Tube

 

[unclesyd]

I'll have to diverge a little from the above post as it has been my experience that Inco 718 fasteners present some very bad habits centered on galling. If this is a make and break application I would keep an eye on tthe component.
We use Inco 718 as set in studs and as stud bolts. We do not have any direct contact with 17-4 PH but with 316SS, A286, Inco 718. For most set in studs we use silver plating and the various stud bolts we use Thermoplte.
Over the yeas I've intended to look 17-4 PH as being very bad about galling.
Having talked about 17-4 Galling I turn around and use in in situation where galling will occur. By Liquid Nit riding the 17-4 PH and running it against Nitronic 60 it will run for ever even though the parts kiss quite ofter. this application is for a drum and sleeve in split case pumps.

 

[EdStainless]

Silver plating, an old trick that I forgot might work here.
And these are rolled threads, right? Cut threads require an extra level of care.

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Plymouth Tube

 

[aroundhere]

these are cut threads. 1.5-8 stub acme. The stubs are much more forgiving than V's.

 

[unclesyd]

If backward compatibility isn't a problem you might want to look at the Spiralock Thread Form. This is the only thread form that NASA would allow to be reused on the Shuttle. I've used it on several demanding make and break situations.
I would give them a call.

 

[Metalhead97]

aroundhere,

It's interesting that you would go from a low alloy steel with a BCC matrix to a IN718 with a FCC matrix when 17-4 PH is FCC- especially when 17-4 and IN718 have roughly the same hardness ranges. Was it done for the corrosion resistance? You could try chrome plating the 17-4 PH since that would provide the best galling resistance and is a resilient coating.

MH

http://www.linkedin.com/pub/luke-autry/1b/510/566

 

[SJones]

http://www.eng-tips.com/search.cfm?q=galling&action=search

Steve Jones
Materials & Corrosion Engineer

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