Nitriding barrels????????????????? benefits?

[g7777777]

This is a surface hardening process used for some steels- has anyone used it for high velocity barrels and are there any documented test results?

regards from Iowa

Gene

 

[cmillard]

mmi tru tec treats barrels. i believe in the guns of the week there is a rifle with this treatment process done on the barrel. from what i have read, there is significant barrel life gained by having the barrel treated. my next barrel with have this process done. just have to be sure to have the barrel chambered and headspaced first, then unscrew it and send it off. regards, also from iowa.

 

[camac]

I don't know much about this but I would also imagine you should run in your barrel first - then clean very well somehow?

 

[swede7]

Do a search on here, it's been discussed before and there are lots of varying opinions on it. Me? Just sitting on the fence...

 

[TheBlueEyedBear]

These URLs should provide some interesting reading for you:
http://accurateshooter.wordpress.com/2009/10/10/salt-bath-nitriding-for-barrels-whidden-is-impressed/
http://accurateshooter.wordpress.com/2010/02/01/shot-show-report-mmi-trutec-salt-bath-nitriding-for-barrels/

 

[glo]

I don’t think enough folks have done the process to see if there is any benefit. If you do nitride your barrel please keep good records of how many rounds you’ve shoot, throat wear and bore cleaning. Let us know when you think the accuracy is coming in and starts to go away. This will better help us understand if there is any benefit to nitriding a barrel.

Personal I think there will be little benefit. Nitriding is used on wearing surfaces of metal that see compressive forces. The inside of a barrel sees expansive forces. The next barrel I get will be Cryo’ed (cryoization stabilizes the crystal structure of the metal). I think if you nitrided a barrel after you cryo’ed it, there could be benefit. But this is only a wild guess.

 

[Waskawood]

In my previous life as an aircraft mechanic, nitrided cylinders were very suseptible to rust. You would have to keep it well oiled.

 

[Bob3700]

Nitriding aircraft cylinders vs stainless steel bbls has a little bit of difference.

The bbls are not prone to rust due to the parent metal. Acft cylinders are made of a steel that would rust whether you nitrided it or not.

According to the processor, the bbls should have no more than 30 or so rounds thru them. Once nitrided, they cannot be set back or recrowned as the surface is too hard. They can mask the crown for a distance and that will allow for recrowning.

Not enought rounds thu the bbls yet to comment on increased round counts. The bbls do come back and look like they have been factory black/deep blue finished.

We have six bbls that have been treated and are keeping records on round counts.
They range from 308, 6XC, 6.5x285 and 6.5x06 and a 7mm wsm.

Those that have had the treatment done have noticed an increased ease with cleaning the bbl.

RGDS

Bob

 

[Webster]

I don't see how you could nitride the inside of a 0.243" tube 26" long. The nitriding is usually done with a nitriding gas atmosphere at around 1000 degrees F. The nitrogen diffuses into the surface of the steel and forms an iron nitride compound. How do you get a continuous stream of the nitriding gas inside a barrell then cool it from 1000F without warping it.

 

[glo]

I’m not an expert in this process by any means, but here is what I understand.

Side bar: The reference above about the aircraft cylinders being nitrided, I believe was a slight miscommunication. The cylinders are sleeved with cast iron. It is the aluminum pistons that receive the nitride process.

Anyway, under the pressurized and controlled conditions of the nitriding process, the nitrogen (in the form of ammonia)that is introduced into the container will seek out all exposed surfaces. In lay terms its called a gaseous equilibrium. Meaning that if you add an extra 10% of nitrogen to the mix it will seek out the entire volume of the container to be equally 10% everywhere.

This is because the environment is controlled and purged of unwanted gasses first. Even with a substantial amount of oxygen present, because both gases are so close in atom weight the nitrogen seeks out all portions of the container by volume.

The only way the nitrogen gas introduce into the process will not find the surfaces of the barrel bore is if you plug or block them.

 

[glo]

To reply to my above post and explain hardesses, the hardness of the nitride process is about 55 to 60 on the Rockwell “C” (Rc) hardness scale or equivalent to about 300,000psi in tensile strength.

Your untreated chome-moly or stainless steel barrel is about 30 Rc (140,000psi) and 1 Rc (76,000psi) respectively and your action is an industry standard of about 42 Rc (118,000).

For other comparisons, a hacksaw blade is about an Rc 40 (180,000psi) there is no comparison to a diamond or carborundum. Both the diamond and carborundum are not even on or convertible to the Rockwell scale. The Rockwell “C’ scale stops at 8 on the Mohs hardness scale. A diamond is a 10 and Carborundum is equivalently hard on the Mohs scale. So as you can see as comparison, once you have nitrided something (steel alloy) the surface is extremely hard.

 

[Robert]

glo,

But the Durferit (call it Melonite if you prefer) is a salt bath process, not a gazeous one.

'QPQ' means 'Quench Polish Quench', and, what really bothers me here is the '"P" inbetween...

Who knows what t really implies for a barrel bore profile?

R.G.C

 

[Webster]

Check out this website for info on hot gas erosion.
http://www.schuemann.com/LinkClick.aspx?fileticket=66qvYywiHmo%3D&tabid=67&mid=445

Thirty years ago I sectioned a 6mm Rem steel barrel and looked at it on a microscope. The first 4" or more from the chamber look like alligator hide. I should redo this with my 7000 round Douglas SS barrel. It appears that all of the serious looking damage is from hot gas erosion. Huge amounts of metal are eroded away ahead of the chamber. I don't think that increasing the hardness by nitriding would have any affect on hot gas erosion. Even if nitriding reduced bore wear it would not prevent hot gas erosion ahead of the chamber . Do a Google search for hot gas erosion, you could find many interesting articles.

 

[butchlambert]

Looks like a lot of speculating from folks that have only heard what their buddies at the range have told them. QPQ melonite is a low temp salt bath nitriding. The first 6ppc barrel that I had done was a Kreiger. I normally get about 1000 rounds before accuracy tapers off. This one was shooting good at 5000 rounds. An un named barrel company bore scoped it at 4500 rounds and said no alligator or throat erosion. I did recrown it once. You just need to get below the surface hardening and crown as usual. They are a little easier to clean. I shipped this barrel to a gun shop teacher for his class work. Strangely enough it disappeared. I believe the US Army is using QPQ barrels now in tests.
I believe if you check, the corrosion resistance is much better after treatment. It is not a coating, it is kinda like a low temp case hardening. You need to question people that have tried it and not some guy that heard so and so.
Butch

 

[Dgd6mm]

Thank you Butch Lambert for the great info.

 

[cmillard]

well said butch!!

 

[Bob3700]

Glo,

you wrote: The reference above about the aircraft cylinders being nitrided, I believe was a slight miscommunication. The cylinders are sleeved with cast iron. It is the aluminum pistons that receive the nitride process.

The barrel of aircraft cylinders ARE nitrided, in fact, once this process is performed the cylinders are paint marked to indicate that the cylinder is nitrided.

The piston's are forged aluminum and the nitriding process is not performed on them. I am not even sure that it would work on them as this process may only be appropriate for a ferrous material. You can check this out on the Lycoming or Continential aircraft engines website.

Bob

 

[glo]

Again I’m not an expert in the nitriding process. Having been part of the drag racing business in an earlier lifetime probably does not make me even qualified to comment on piston driven aircraft engines.

Here’s what I know: If an engine block is cast iron or aluminum with cast iron sleeves it has a baring surface of 46 Rc (212,000psi). If the engineers want to nitride the cylinders to 55 Rc so be it.

Yes you can nitride aluminum as well as titanium, molybdenum and other exotic stuff. Some big block Chevy's for the Can-Am sieris (4.44 Bore) during the early 70's had the inside baring surfaces nitride to run aluminum on aluminum.

Also to reply to the above about melonite (QPQ) being a “low” temperature, liquid salt bath process, yes I am a where of that. Low temperature is 1,000 degrees Fahrenheit and yes the liquid will attain equilibrium during the process as it impregnates all exposed surfaces. Liquid salts of ferric nitride will attain a hardness of 55 Rc to about 6 thousandth of an inch in depth to the surface; just the same as the gaseous process.

 

[VWguy]

i race vw's and all of my chromoly cranks are nitrited. most of the pistons are coated with various products. but can you imagine rings ever seating on a nitrited cylinder wall? no friction.