Fracture Toughness of 304 and 17-7

[bravedog]

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.

 

[metengr]

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??

 

[EdStainless]

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

 

[bravedog]

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.