Hardened 440C Stainless Vs Hardened Carpenter 465

[Hazza_Med-Device]

Hello,

I am trying to find the best material to make a Torx 25 driver to be used in surgical operations. Currently we are using Carpenter 465 on our T25 drivers and the tips sometimes shear off inside the screw we are trying to remove.

What is the hardest and most practical material? Will 440C be able to offer any improvements over 465?

Thank you for your help.

 

[3DDave]

All that comes to mind is that if the tip is shearing that it's just a matter of time before the head of the screw is twisted off.

It looks like 440C can be slightly stronger.

 

[MagBen]

440C can get you higher hardness, however, C465 will give you excellent notch tensile and fracture toughness which 440c cannot. also, corrosion resistance of C465 approaches that of 304 that 440C cannot offer.
Ask Carpenter to add heavy cold work (if not big sized stock) and H900 condition which will give you extra hardness and tensile. ASTM A564 and AMS 5936 list the lowest aging temperature 950F, but you can go with 900F.

Another option could be a new 440 series UNS S42070/AMS 5898 carpenter develops recently. It has the hardness capabilities of 440C but superior corrosion resistance. Carbides are replaced with nitrides which reduces the amount of Cr being taken from grain boundaries.

 

[EdStainless]

If you are shearing tips then I wonder are they brittle failures or actual tensile overload?
You need to figure this out.
It may be that raising the aging temp and softening them a little will give you better toughness and tolerate misalignment better.

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P.E. Metallurgy