CCIman wrote:"Nitrided' barrels:
Does anyone know if the Glock barrels are nitrided? Any others?
One AR manufacturer (CMMG) uses a "nitrided" chromoly barrel, which they call their WASP finish. Are there any downsides in the process of "nitriding" the barrel (vs. chrome lining a barrel) that makes this a bad idea? Assuming that all is done correctly, I am currently thinking that a nitrided barrel is more wear/corrosion resistant than chrome lined. If I am correct on this, why not more of this in the rifle market?
What you are thinking of is actually "carbonitriding" or "nitrocarburizing". One is via gas medium and the other via cyanide salt bath but they produce essentially the same coating. The "Tenifer", "WASP" and other coatings are just fancy tradenames for these very common surface modification heat treatments.
"Nitriding" is a process that imparts ONLY Nitrogen into the surface of the steel, typically with cracked ammonia gas. "Tenifer" and "WASP" do more than that, they also add Carbon.
If you are looking at surface hardening a low-alloy steel then "nitrocarburizing" is just fine. Just remember that underneath that layer of hardness you still have soft steel (one of the alledged reasons for Glock kabooms, by the way). This is also a CHEAPER process than straight nitriding, since it adds two interstitial hardening atoms at once. That's why it is so popular.
If you are looking at surface hardening stainless steel then STAY AWAY from any and all "nitrocarburizing". Why? Because the intruding Carbon will bind with the free Chromium (which you need 12% minimum of to be considered stainless) and bind it up as Chromium Carbides. This is the EXACT same phenomenon as "weld sensitization" sometimes seen in stainless steels (for you welders, this is the reason the "L" grades like 316L were invented, less Carbon meant less weld sensitization). The result will be a loss of the "stainless" quality of the steel. If you are EVER going to "nitrocarburize" then you should NEVER use stainless. PERIOD.
None of these surface modification heat treatments improves the overall corrosion resistance of the steel. I know folks claim that they do - but they don't. You can show a resistance to forming rust bubbles but that's only because the matrix is harder. After a certain amount of time, though, corrosion will still claim its victim. In fact, with stainless steels that have been "nitrocarburized" they will actually corrode MUCH MORE QUICKLY than if they had been just Nitrided (or left alone entirely).
Chrome acts PARTIALLY as a barrier coating so you do get some corrosion resistance boost. It ain't perfect, either, but it is pretty darn good and has the advantage of being time-tested.
As to the "wear resistance" question - this is not nearly the common boogeyman that it gets played up as. In rifle barrels there is simply more erosion due to the passage/redirecting of hot gasses at the throat (and muzzle) than damage due to "wear" from bullet rubbing. Even if there were NO WEAR AT ALL from bullet passage you would still need to replace most barrels at the same time due to the throat and muzzle erosion issues. Hardness is not a factor in these places at all - steel chemistry and manufacturing process is a factor.
If it were ME and I wanted the best lasting barrel for all time I'd go with a vacuum-arc-remelted (VAR) grade of 15-5 PH stainless in the H1000 heat treat condition that was then GAS NITRIDED. Why? The VAR grade gives you finer grain size which should help with intergranular attack (IGA). The H1000 condition gives you a temper that can survive being gas nitrided at 975 F without softening. Of course, you'll never find anyone making a barrel like this (note that 17-4 is not made to VAR grade to my knowledge, it is strictly an ESR grade of steel).Chrome is just fine. I encourage ANYONE who can buy a chromed barrel to do so. Playing around with fancy tradename coatings might help if you are a journalist with one of the various gun periodicals but otherwise it is just silly.
As to the aftermarket stuff you mention - provide a link and I'll provide an opinion.
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