Proper Post-Heat Treatment optimal HRC range on 416R

[jcsr_75]

Hi everyone, I am considering if gun barrels we produce really require Heat Treat as part of the process. Though, it has been customary to send them out for this procedure I can understand that 416R is pre-heat treated. Regardless, I tend to believe it is not necessary. Also, assuming it is what would be the best HRC values/range, maybe somewhat in between 38 to 42?

 

[FredC]

I have never worked with 416R, but we have machined 1000s of feet of 416HT and a couple of lengths of annealed material. The 26 to 32RC material seems to be easiest machining compared to 32 to 36RC which will finish marginally better.
The annealed material did not finish anywhere as nice as the other two.
I would think that your material supplier will have a metallurgist who could give you specific answers.

 

[jcsr_75]

Thank you Fred, I will do as you suggest.

 

[FredC]

Thank you Fred, I will do as you suggest.

I doubt if your competitors would volunteer trade secrets, but a little research on the ends cut off competitors' barrels could give you some clues. Even if you do not have a super accurate hardness tester, you could send the pieces out for testing. For others listening in on this conversation it is traditional for barrel makers to supply a barrel with an additional inch on each end of a custom barrel. I have a new stainless 6.5mm barrel on the shelf that was ordered 26 inches long that is actually 28 inches.
On the subject of 416R do you know what the free machining additive is? I have a suspicion that it is selenium. I have run 303Se where selenium is used as a substitute for sulfur. It is free machining after a fashion but a lot less likely to crack in heavy swaging. We used it for making fittings swaged on to aircraft cable.