Affect of LN2 bath on nitrided 15-15 stainless steel

[NHATLEY6]

Hello,

I am working on a project that currently uses a LN2 bath to chill shafts for an interfearence fit. The shafts are made out of 15-5 stainless steel and need a core temperautre of -60 F to assemble with the outside component. The question I have is the shock on the steel and its affects on the microstructure. The parts are submerged for a few a few minutes. One part is carburized 15-5 stainless steel and another shaft is nitrided 15-5 stainless steel. The main concern is that the nitrided surface inhibits the contraction of the internal material of the shaft thus creating internal stresses.Recently we have reduced the rate of cooling by placing the shafts in an environment with ln2 but not directly in contact.


Thank you for your time, any advice would be helpfull

Nate

 

[EdStainless]

Actually liquid nitrogen is not a very severe quench. It boils so much that you get a gas blanket around the part that 'cushions' the cooling.
My concern is about the difference of thermal expansion between the core and case.

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Plymouth Tube

 

[NHATLEY6]

Thanks the unit that is in question is about .225 in thick so.. im not sure if this is thin enough so that thermal expansion wouldnt affect drasticly. So the nitrided surface should have a different expansion rate correct?

Thank you for your time
have a good day