Machinability on Nitrogen strengthened stainless steel

[MagBen]

I have two N strengthened steels, one has N .1%, the other .2%. The lower N one has a lower yield strength but higher elongation. Are you expecting poorer machinability from lower N steel?
I have a customer claim for lower N steel saying it promoted the hardening during manufacturing process while cutting as heat generated was higher due to the increase in malleability. Make any sense to you? Poor machinability here meant breaking tools/scrapping parts.
Thanks for your reply!

 

[EdStainless]

Sounds like tooling optimized for harder material and he forgot (didn't bother) to make changes for softer material.
I find this a little hard to swallow though, these are both so much harder than annealed 304 that I don't see how this minor variation could cause his process to fail.
The higher N material will actually work harden more, but it may be hard enough to start with that it cut cleanly.
If the softer one was smearing and sticking to the tooling the operator should have noticed that.
Deeper cuts and less feed, more coolant, and different insert geometries. Basic machining.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Thanks Ed! what is the reason higher N material works harden more?
This is actually a CoCr-based stainless, strictly speaking, a high temperature alloy. The extremely high work hardening rate makes this alloy difficult to machine. Since higher N could decrease the stacking faults per some literature, could it be possible lower N increased work hardening, making it harder to machine?

 

[EdStainless]

I suspect that the softer material is being smeared while they are trying to cut it.
That smeared material will be strained a lot and will work harden a lot.
The harder material may cut more cleanly and so they are working it less.
Is this an age hardenable material?

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

No, it is not hardenable like austenitic SS. mechanicals are normally controlled by warm worked.

 

[metengr]

I think the attached reference material may be of help

https://www.cartech.com/globalassets/literature-files/carpenterguidetomachining.pdf