QPQ is prescribed when a smooth surface finish and maximum corrosion protection are required. For many applications, this finishing process provides a surface condition that protects against corrosion and wear superior than hard chrome or nickel plating. Liquid Nitriding Liquid nitriding is a subcritical surface enhancement process with one of the longest track records of success of any case hardening technology.
During the salt bath nitriding process, the metal surface is enriched with nitrogen and carbon. A two-part nitride layer consisting of a monophase compound layer and a diffusion layer is formed.
Total depth ranges from 0. Hardness in the compound layer ranges from approximately HV on alloyed steels to HV on high chromium steels. The nitrogen-rich inter-metallic compound layer mainly contains iron-carbonitrides and, depending on the type and proportion of alloying elements in the base material, special nitrides.
In the metallographic analysis the compound layer is clearly definable from the diffusion layer as a lightly etched layer. A porous area develops in the outer zone of the compound layer. The case hardness of the compound layer measured on a cross-section is around HV for unalloyed steels and up to about HV on high chromium steels. The higher the alloy content, the thinner the layer for the same treatment cycle.
In addition, unlike a separate layer of a dissimilar metal, the nitrided layer is integral with the rest of the steel barrel and doesn't experience crazing from thermal cycling. It's also much thicker than any additional layer like chrome, so a bore for example would be utterly worn and useless before you'd wear through the nitrided layer.
Nitride, when done to carbon steels, results in very corrosion resistant as well as very hard, durable surfaces. Stainless steels are a poorer choice for salt bath nitriding processes because the different elements in the stainless alloys result in much reduced corrosion resistance, as well as lower heat resistance that's inherent in the underlying steel.
Nitrided stainless means more expense for a poorer performing product. Which surface is harder? Nitride or Chrome? Nitride is considerably harder than chrome lining. Enterprises offers melonite carriers. That is the material of the barrel not the finishing process. And as I mentioned, nitride in general is not the best option for stainless From my understanding there are some lower temperature non-ferritic gas or plasma nitriding processes in development for stainless, but in general, why bother?
Because the specifications say chrome. Despite the apparent advantages there may be some cases where chrome is still a better choice. Something that used to get trotted out often was a couple decades old military test on 25mm cannon barrels where they compared a nitrided barrel not sure what process to the existing chrome lined, and got longer life out of the chrome. Large caliber barrels for cannons and artillery do have some different characteristics than small arms barrels, or it may have just been differences in the process that was used versus current processes.
One thing that is often overlooked in the "newness" of nitride to the firearms market is that it's really not new, even to the firearms market. HK for example has been using nitriding processes since the 60's, most all of their products have used some kind of nitriding mostly gas nitriding on various parts since that time. Nitride has been widely used for parts for the oil industry and especially the nuclear industry for almost as long, as well as automotive and industrial parts and other users.
It just hasn't been traditional for firearms in the US and not "mil spec". Tenifer is correct. I have one and have only used surplus corrosive ammo in my rifle. It holds up extremely well. After almost rounds it still looks like the day I got it. I know thats not a lot of rounds but I've heard stories of untreated components exhibiting signs of corrosion if left unattended after only one shooting session. It appears to clean up and hold up extremely well.
I don't care who ya are, now that was funny! Thank you sir! I had always been under the impression that stainless was harder than CM steel, and its used for match barrels because it maintains a high level of accuracy longer.
Something like CM barrels gradually degrade and wear, whereas SS barrels are harder, and don't wear so much, but form micro cracks, and at rounds caliber dependant parts of the lands chip away in the throat and there is a rapid decrease in accuracy.
My understanding is that stainless is quite soft, at least compared to CM. Hard chrome is well Stainless barrels will wear out faster than a non chrome-lined CM. However, stainless tends to be more accurate.
The military uses hard chrome to make the barrels last longer under machine-gun fire and to improve corrosion protection, but that isn't news to anyone here. LedZeppelin is wrong in this case. Its values are corrosion resistance, and traditionally, the soft-as-butter nature of the metal made it easy to cut very smooth and precise barrels. Unfortunately they don't last as long, and generally require heavy profiles, because of those same qualities. There are some other stainless alloys which are somewhat harder and barrels made of some of those alternatives are available.
Hard chrome is for corrosion protection first and foremost. Barrel life extension is a lot less than you'd probably think, especially in severe duty environments due to crazing and erosion of the underlying steel. My understanding is that they are stainless.
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