[lysander]

Jon are you saying you would not Nitride the receiver?

Ren

Yes, please elaborate on Ren's question, Jon.

Thanks,
MM

I believe this has to do with the heat treatment of the receiver, bolt and other parts noted.

Nitriding requires the part to be placed in a bath at around 1000 F. this is above the tempering temperature used during the heat treating of these parts.

Heating these parts to 1000 F will alter the strength.

 

[lysander]

Nitride won't remove the heat treat. Unless I'm reading wrong.
http://www.blacknitride.com/frequentlyaskedquestions.html

It will change the temper.

The heat treat for a 8620 receiver is carburize at 1600 F for a case depth of .018", quench in oil at around 100 F, temper at 480 F for one hour, the surface hardness will be 59 to 67 RHc.

Bringing the receiver to 1000 F will change the temper.

This statement...

2. If the pre-hardened component is pre-tempered, or non-pre-hardened above subsequent temperature, core hardness will not change significantly as a result of the Black Nitriding process.

...only applies to parts that are tempered at temperatures above the nitriding process temperature. Since the tempering temperature for a receiver is below the nitriding temperature, raising the part temperature above the initial temper temperature (480 F) will significantly change the material properties...

More in nitriding:

Nitriding is carried out at temperatures below the transformation temperature of alloy steels, so that with proper manufacturing techniques, there is little or no distortion as a result of the process. Parts to be nitrided are heat treated to the proper strength level, and final machined. The parts are then exposed to active nitrogen at a carefully controlled temperature, typically in the range of 925°F to 985°F. This temperature is typically below the final tempering temperature of the steel so that nitriding does not affect the base metal mechanical properties.

In the case of receivers and bolts, 1000 F is well above the final tempering temperature, so it will affect the part's properties.

 

[lysander]

I ask because I, and several other members here, have GunWorks of Lower Alabama receivers that are factory nitride finished and it was my understand that their receivers are nitride finished after heat treating.

Factory nitriding can be different from aftermarket nitriding.

With factory nitriding, the nitriding process can be worked into the part's overall heat treatment, with aftermarket nitriding, you have to start with a heat treated part and NOT alter its properties.

By the way, barrels are tempered around 850 F to 950 F, so they do not see a change in temper. Which is why after-market barrel nitriding is much simpler.

 

[lysander]

raising the part temperature above the initial temper temperature (480 F) will significantly change the material properties

Right on, but where'd you get 480?

That's the heat treating recommendations for carburized 8620 to achieve the harnesses I specified and maximum strength. That heat treatment gives a tensile yield of 135,000 psi, going to higher tempering temperature results in a softer core, and thus not as strong.

Incidentally, I ran across a print for an M1 receiver, they were specified to carburize at 1550 F to 1600 F, temper at 400 F for one hour, so they were a tad harder, 61 to 69 RHc.... that is in the same ball park, if not exactly the same as the M14 receiver.

Factory nitrided receivers and bolts are probably not carburized, as there is no need, the nitriding will harden the surface adequately. Un-carburized 8620 tempers at much higher temperatures. Tempering un-carburized 8620 at 1200 F will give a yield strength of 101,000 psi, at 800 F you can get the full 135,000 psi.

 

[lysander]

Something else occurred to me, it might just simply be a liability issue. The guys doing the nitriding have no clue how these critical components were heat treated by the original manufacturer, and what effect his heating the parts for nitriding will do to that heat treat. . .

Barrels are different an annealed barrel shouldn't fail under a proof load, so no worries there.

 

[lysander]

I disagree with only the part about the nitride people knowing the heat treat process. The folks from the link I gave started off in the heat treat biz.
The rest makes sense enough to me I'll take you at your word.
The barrel, gas system and the gas cylinder the only parts that really benifit having nitride anyway i guess. Unless it's more for looks.

They know the heat treatment they give to their parts, and how they would do it, not the exact heat treatment done to a critical part by someone else....

Short of cutting and doing some destructive testing, you really can't tell much about the actual heat treatment given to a part, unless you watch them do it.

Oh, and nitriding is a far better corrosion resisting process than phosphate coating, aka Parkerizing. It also is a very good in wear resistant properties.

 

[lysander]

I wonder if you could nitrite barrels that had corroded bores (dark bore) from corrosive primers.
One with good rifling and muzzle. The one's that shoot with good accuracy but no matter how well you clean the bore that patches come out black or dark brown. Like all the M1 Garand barrels probably in the millions that have "dark bores".

Nitriding won't fix a damaged bore. Basically, it is a form of super case hardening.

And to nitride it, you will have to clean all the corrosion out of the bore, clean, bare metal.

 

[lysander]

Disclaimer: Ya'll are way over my head on this stuff so I hope you don't get upset with me asking what might be basic questions.

1. I've seen thermal images of suppressor shooters depicting the suppressor at 700f+ degrees after rapid strings. Does this 700f hanging on the muzzle change the temper of the muzzle for bad or better?

2. Years back I worked with some Electroless Nickel coated (AKA Germany Nickel) wear parts (industrial electric-submersible pumps). I also have a 9mm handgun that was "factory" coated - slide, trigger, external barrel. On the pumps we had the volute and impellers done and the iron motor housings were coal tar epoxy coated. Not sure exactly where these pumps went but nine months later the EN parts were about all that was left. The lubricity & corrosion resistance impresses me and I wonder if it has been tried on rifles or why not?

Shooting 1 round every two seconds for a minute (a very reasonable rate) will get the barrel temp around 200° F.

Three 20 round magazines at 1 round per second gets the barrel to almost 400° F.

A twenty round magazine every 5 seconds for a minute (barely do-able in a semi-auto, if you are good at magazine changes) will get the temperature up to around 1000° F.

The heat treatment of barrels is designed to take upwards of 1200° F for several minutes without damage.

As to #2, I am sure someone has tried it.