Black Oxide Coating of Nitronic 60 1

[tbuelna]

I am considering using moderately strain hardened (160ksi uts) Nitronic 60 bar for a shaft design. The shaft body will be loaded in shear and may experience a very small amount of sliding at the contact with the mating bore surface. The mating part is 17-4PH H1150 cres. I need a cosmetic black finish on both parts that will not produce a dimensional change. I know I can use MIL-DTL-13924, cl. 4 black oxide on the 17-4PH part, but the spec is not clear about using it for Nitronic 60, which I believe is an austenitic alloy.

I came across an old post from kenvlach that described some anti-chafing/wear benefits of AMS 2485 black oxide coating. This interested me so I purchased a current copy of the spec. But after reading AMS 2485K it was not clear to me whether this process is suitable for use with corrosion resistant steels like Nitronic 60. Sec. 8.5 states "Assemblies containing parts made of metals other than steel or iron alloys should not be processed....", so would this exclude stainless steels?

I'd like to use the black oxide process described in AMS 2485, so can someone tell me if the process is suitable for use with Nitronic 60? If not, is MIL-DTL-13924, cl. 4 black oxide suitable for use with Nitronic 60? And if neither process is suitable for use with Nitronic 60, does anyone know of another compatible coating that will produce a cosmetic black finish with minimal dimensional change?

Thanks in advance for any help.
Terry

 

[EdStainless]

I would like to see you do some microhardness readings on the swaged ends.
The question in my mind is do you have safety margin, or is that material too brittle.

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Plymouth Tube

 

[tbuelna]

Here are a couple close-up pictures of the swaged end of the pin. To give you some idea of scale the OD of the D-shaped retainer isy .360". The texture you see on the end face of the swaged pin rim is from a vibratory deburr operation done on the pin prior to swaging.

EdStainless- The working stress in the swaged section of the pin is extremely low. The purpose of the swage is to keep the D-shaped retainer attached to the pin, and the purpose of the D-shaped retainer is to keep the crowned roller from sliding off the end of the pin. In service the retainer and swage joint are only subject to a very small axial thrust force (<10 lbf) produced by the crowned roller, so the swaged section of the pin likely has very generous stress margins.

As for the body of the 17-4 H1025 pin, the peak stress occurs at the fillet where the pin diameter steps down to fit inside the roller. The lower pin body is mounted in single shear and the radial forces acting on the overhung roller produce some bending in the pin body. The fatigue loads are fully reversing each cycle so this creates alternating tension/compression stresses in the small transition fillet of the pin body. But based on an FEA the peak tensile stress level in the fillet is below 15ksi, and the number of fatigue cycles the pin will see in service is less than 6x10^4. So I think it should be OK.

I'd love to do what you suggest regarding microhardness testing of the swaged section of the pin. But as I noted, this is a garage project and this kind of lab testing is not currently within my budget.