17-4 stainless wheel rolling on 316 stainless flat bar

[pbc825]

Howdy folks,

I'm working on a project that has a 16" diameter stainless steel wheel which I'm proposing to fabricate from 17-4 stainless rolling on a 316 stainless steel flat bar. Wheel loads are in the 45kN range. Client has raised the question of galling. Can anyone provide insight on this phenomenon and whether it will be a challenge in this instance. Application is a freshwater gate.

Thank you in advance.

 

[EdStainless]

Galling isn't my first concern. You would only gall if the wheels don't turn and you have simple sliding.
There is enough hardness difference that galling shouldn't be bad.
You will dent the 316 with any significant load.
Combined with the risk of corrosion (esp on the 17-4 PH) you could end with a fairly bumpy track.
You might look to see if you can find Nitronic 50 bar to use in place of 316, and maybe you can find bar that has been cold rolled to higher hardness. The Nit 50 will also have better galling resistance.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

In terms of galling resistance, N strengthened 23Mn-21Cr-1Mo SS (ASTM F2229) is an even better choice. It is essentially Ni-free stainless that is capable of very high strength in excess of 200ksi. The resistance to pitting and crevice corrosion is superior to 316. galling is better than Nitronic 50.

 

[EdStainless]

Yes Ben, S29108 is great, but the last time that I checked you could only get it in small diameter bar.
Nit 50 (S20910) is much more common, and does better than any of the 3xx alloys.
It is called XM-19 in ASTM and it is covered by a boatload of specs.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Ed, we are offering up to 2'' bars (internal name BioDur 108)! But of course, if you want a high tensile, a high cold work is needed, which will limit the bar size. note this alloy can be offered 4 conditions: annealed, condition A,B and C. condition C has the highest strength.

 

[pbc825]

Thank you kindly Magben and Edstainless. I'll revise the specs to suit.

Best regards.

 

[tbuelna]

If you can profile your track and wheel surfaces to ensure the contact stress levels are kept within the galling threshold limits for your materials (8ksi for annealed 316), you should be OK. If you want an extra level of protection from galling, you can apply some type of dry film coating to the contact surfaces.

 

[pbc825]

Thank you tbuelna.

What ranges of hardness does Nit 50 come in? I would suspect the cold rolled condition would offer higher hardness than the annealed state. Does the state modify the yield and ultimate strengths?

 

[EdStainless]

With any of these 2xx series alloys you would want it in the as-cold-worked condition.
It raises tensile strength (UTS and yield), hardness, galling limits, and lowers the ductility some.
In most cases material with roughly >100ksi min yield and a UTS over 125ksi will get you good performance without being too difficult to work with.
(as a note we cold draw 21-6-9, Nit 40 tubing for use in aircraft hydraulic systems, it is 140-160 UTS and it still have over 20% elongation)

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

most of times, it is cold worked to boost strengths but also with exceptions, such as fastener applications that use annealed condition. This N-strengthened alloy can be cold worked up to 70%, due to its high work-hardening rate, high strengths with good ductility can be achieved with less reduction. 15% cold work can give you 165 UTS, still with 20% elongation, hardness>30HRC.