Heat treat high chrome stainless ?

[jim hardy]

I'm a retired EE tinkering in my workshop.
Materials is not my field so I'm asking for a pointer.

I have an old steam turbine blade and suspect from researching on 'net it's alloy 17-7 or 17-4(AISI 630). It's a big one, 44inch so strength was important when originally made.
It gives orange sparks when grind on it.
Am cutting it up for my friends (retired electrician, retired carpenter and retired trucker) and myself to make squirrel skinning knives.

Would you point us in right direction for heat treat?

From what i can tell from Allegheny Ludlum datasheet we should give it four hours at 1900 F air cool then one hour at 900F to get RC hardness into 40's.
I am confused whether we need a quench.



We cut first piece with a torch which got it VERY hot and seems to have softened it considerably from its as-manufactured state.

Does anyone know if we can get hardness into 50's, as claimed by knife manufacturers for their 17-7 ?

17-7 PH - A Chromium/Nickel/Aluminum, precipitation-hardening, stainless steel. The alloy is used for high-strength applications requiring resistance to salt-water corrosion. 17-7PH offers a good compromise between Martensitic stainless steels (heat-treatable) and Austenitic (300 series) stainless steels (non heat-treatable). This is due to the high Chromium/Nickel/Aluminum content.
•Moderate edge holding
•Very good toughness
•Excellent corrosion resistance
•Rockwell Rc 54-56

http://www.knifecenter.com/knifebladematerials.html


sincerely - old jim himself

 

[Navin A S]

It sounds like you are on the right track with your heat treatment plan. Quenching is usually necessary to achieve a hardness of 50's, and this can be done either by air or oil. The temperature of the quench should be around 150 to 250°F, depending on the alloy. For 17-7 PH, it would be best to use an oil quench. You may want to consult a professional heat treating service to ensure that you get the desired hardness. Good luck with your project!