letter 22849

How do I spot galling? prevent galling on 304 on 316?  

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Two questions:

Q1: How do I know if "galling" is occurring? My components are getting stuck together after high load. These components exhibit scratch marks and even metal particles raised on the surface.

Q2: Is this galling aggravated by the fact that my mating components are 304 and 316, which I believe have similar hardness? I am hearing contradictory things on this item.

Here are some solutions I am thinking of pursuing. Any critiques or suggestions would be greatly appreciated!
-Precipitation hardened 17-4 on one component
-Silver plating one component
-Hard chrome plating on one component
-Nitronic 60 on at least one component
-Smoother finish on both components

Thanks!

Mina Leung
- Santa Clara, CA, USA

As I learned years ago (the hard way) , you just do not mate 300 series stainless to itself. Sometimes you can get away with it with good lubrication. Silver plating is an excellent lubricant. Chrome or electroless nickel plating one of the surfaces will take care of the problem in virtually all cases. Plate the easiest or cheapest to plate part. Hardened 17-4 will do better than 300 series on one part. Here again, do the cheapest to manufacture part. I don't think that I would go to Nimonic unless you have a good reason. You have not said how the part is used or any of the particulars, so the above is a generic answer.

James Watts
- Navarre, Florida

If environmental conditions permit, use type 410 stainless for one of your components. The difference in hardness will prevent galling. The 410 still has a degree of corrosion resistance and good strength characteristics.

John Hetherington
- Montreal, Canada

I make a lot of stainless steel and nickel alloy threaded components. Experience has shown that smooth surfaces will gall more often than rough surfaces. Buffing threads with a wire brush will help prevent galling.

Also coat threads with an anti-seizing compound such as Kopr-Kote.
If you have the option, do not thread like materials together.

Sheldon Nadeau
- Red Deer AB

If you are interested in solving your galling problem, coat one of the mating surfaces with "Thickfilm Ion Metalizing Process". We coat high nickel alloy, stainless steel, inconels, and and various types of substrates and have proven results for anti-galling.

Brent Steadham
- Houston, Texas

I have heard that using a stainless steel bolt and a stainless steel nut increases the potential for galling. Is this true? I have also heard that using a galvanized nut on a stainless bolt solves the problem. Is this true as well or could we be better served by just providing a lubricant? Thank you.

Matt Dunlap
engineering consultant - Pittsfield, Maine, USA

Reference the Stainless Steel(SS)bolt and nut.

Yes, by using a SS bolt and a Steel nut the galling issue should be corrected. You may also want to investigate what grade of bolt and nut you need for your application. i.e. Grade 2,5,8. The following website has a decent review of the differences between grades, and information on how to read the symbols on the bolt heads.
www.americanfastener.com/technical/grade_markings_steel.asp

Kamm
- Calgary, AB, Canada

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