Stress rlieving 416 after button rifling.

I'm a newbie to this, but in another thread I was told I had to stress relieve the barrels before profiling. These are pistol barrels so about 60% of the OD will be cut away except where the lugs remain. The blanks started out at 1" and the first barrels are .380 caliber.
I have a HT furnace so what I need is the time and temperature needed. I looked up articles on the web and found this one interesting;

Stress Relieving

Stress relieving below 400°C is the most common practice, but the result is only moderate stress relief. Stress relieving at temperatures of up to 425 to 925°C will significantly reduce residual stresses which otherwise cause dimensional instability or stress corrosion cracking. One hour of stress relieving at 870°C relieves about 85% of residual stresses. However, this temperature range can precipitate carbides at grain boundary, resulting in sensitization that affects corrosion resistance in many media. Stabilized stainless steels or low-carbon type steels are preferred to avoid these effects.

Full solution treatment of stainless steels, by heating to about 1080°C followed by rapid cooling, eliminates all residual stresses. However, it is not practical for most large or complex fabrications.
Low Temperature Stress Relieving

While performing cold-working of austenitic stainless steels to improve strength, compressive yield strength and proportional limit will tend to increase with low temperature stress relieving. Stress relieving is carried out at temperatures of up to 345 to 425°C, if intergranular resistance is not important. Higher temperatures will degrade the material strength and, hence, they are not preferred for stress relieving cold-worked products.

Also, I found this here in PM;
https://www.practicalmachinist.com/...ndex2.html?highlight=stress+relieve+416+steel

That's about a rifle barrel, but a pistol barrel may be reduced much more and perhaps even eccentrically.

The first article mentions low temperature SR, but it may be noteworthy that higher temperatures, though more thorough, cause a loss of strength and hardness (In preheat treated 1/2 hard steels I assume) which lowers the longevity of the barrel. Should I try 400C (752F)? How long, 1/2 hour? I plan on tool wrapping, maybe wrap a bit larger and blow argon into the bag? Or will a small piece of paper burn off the oxygen enough?
Thanks in advance for any help.

No info in Machinery's Handbook? How about a steel maker? What about cryogenic SR?

Stress relieving should be done before any machining. Any SR action after any machining could change some dimensions. I know that HK uses M35 steel for their barrels and after drilling and hammering (rifling), the barrels are sent out to HT. After HT, rifle barrels are then checked for straightness and straightened if necessary by simple manual bending and the old eyeball. The guys that do that are the highest paid in the factory. Pistol barrels are not checked for straightness.

Pistol barrels are not checked for straightness.

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I suspect that it's the last inch of travel that counts for accuracy as far as the bullet is concerned, leaving the distance between the sights aside. I think I'll try the 400 F for 1/2 hour, at least it shouldn't hurt anything.

What does the barrel manufacturer say? Non of the materials you refer to mentions 416. They mention other types but that does not apply to your barrel material.

partsproduction said:

I suspect that it's the last inch of travel that counts for accuracy as far as the bullet is concerned, leaving the distance between the sights aside. I think I'll try the 400 F for 1/2 hour, at least it shouldn't hurt anything.

Click to expand...

Well it might, 4xx stainless is martensitic (different than 3xx SS)… If you bought it in a certain strength (hardness #) you should post that up. Carpenter doesn’t contemplate stress relieving 416, for heat treat just take it up to 1700/1850°F and quench in 220°F oil. Then temper for taste of your choice.

Cryo is only done for retained austenite, that’s only gonna happen with Q&T 431 or 440C (higher carbon) SS’s.

3xx (austenitic) stainless’s can benefit from stress relief but they are a totally different structure with different mechanical tendencies.

Good luck,
Matt

A very good read.
The Making of a Rifled Barrel, FirearmsID.com
I've been involved in a lot of cryo testing with barrels.Most of the "cryo" guys do not have the equipment to do a true cryo. I did this with one of the largest custom barrel mfg. It does make the steel easier to machine. Found no other advantage and this included blind testing. I could determine which were cryo'ed as I machined the chambers.
I believe about 600C is a good stress relief and temper for the rifle barrels.