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Fracture Toughness of 304 and 17-7

Fracture Toughness of 304 and 17-7

Fracture Toughness of 304 and 17-7

(OP)
Does anyone know where to find fracture toughness data for stainless steels?  I have a metal tube that gets threads machined on the OD.  These threads are *sharp* so it creates a perfect notch.  I want to make the tube as strong as possible, but the user may pry on these tubes while using them (high strain).  If I pick 304 fully hard, it will be strong, but brittle.  If I pick 17-7, it will be stronger yet, but still brittle.  Can I just use fracture toughness as a guide to pick the right material and condition?  If so, where can I find that data?  Tube is 10.5 gauge.  It is used in the medical field so it must be biocompatible.

RE: Fracture Toughness of 304 and 17-7

bravedog;
I would be more concerned about low cycle fatigue behavior versus fracture toughness in the application you describe. In addition, fracture toughness data will not provide useful information. I would be more concerned about local yielding versus fracture. Can't you roll the treads to reduce stress concentration??
 

RE: Fracture Toughness of 304 and 17-7

Roll the threads and then heat treat to the RH950 condition (or maybe use 1000F aging).  This will be strong and tough.

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Plymouth Tube

RE: Fracture Toughness of 304 and 17-7

(OP)
Some clarification:
   Threads are on the OD of the part.
   Part is disposable - single use only
   Thread height is about 40% of the total wall thickness.
   I would rather the part yield and stretch rather than break.  The threads cannot snap off while in use!

I found Custom 465 which looks like a good application for that material.  I just need to pick the right heat treatment.  I think that the most ductile material with the highest strength would be the winner... but those properties always fight each other.  I am thinking H1050 but it looks like I have some testing in my future to pick the right one.

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