Home Forums Hunting & Shooting Custom Rifles & Wildcats salt bath nitriding/melonite?

greentimber, what numbnuts did you use? Salt bath nitride greatly increases corrosion resistance. I have had several barrels done and it greatly increases the life of the bore. Didn't make them shoot better, but they shoot no worse.

Not necessarily on stainless. This is well established (as SW discovered on the M&P series of pistols). A few seconds of searching turned up:

"Surface hardening of steel and iron (to improve wear resistance) can be done by either allowing the surface of metals to react with either Nitrogen (nitriding), Carbon (carburizing), Boron (boriding), etc. TENIFER is termed for a chemical bath nitriding process whereby nitrogen is chemically released and introduced into the surface at a suitable high temperature to allow the chemical process to take place.

Using the liquid bath techniques, the temperature requires to activate the reaction is about 550 to 580 Celsius. The bath is performed in a molten, nitrogen-bearing liquid containing either cyanides or cyanates. However, cyanide-free liquid has also been used to release Nitrogen and then allow it to react chemically with steel (iron)at the surface (modern techniques).

Interestingly, when using the cyanide-free liquid, Tenifer is actually the salt bath nitro-carburing technique because it starts (first reaction) with Carbon-Nitride (CN) and allows it to react with Oxygen (0)to produce Nitro-carbon-dioxide byproduct plus Nitrogen. The simultaneous second reaction takes place when nitrogen (N) is in contact with Iron (Fe) to form FeN (iron-nidride).

The tenifer coating "composition" of Glock's steel slide is essentially that of FeN.

It is interesting to note that FeN coating is used mainly to increase the surface wear resistance to against galling and wear. The corrosion resistance is also better for iron and conventional steel that are NOT stainless steel. Most stainless steels need not to be nitrided. The reason is stainless steel has chromium to fight against corrosion and rust (this is why we call these material stainless). However, nitriding a stainless steel will almost always lower the corrosion resistance of the stainless steel. This is because the nitrogen will also react with some of the chrominum (Cr) at the surface of stainless steel to form Chrominum-nitride (CrN).

Obviously, gas-nitriding is a simpler process (but not necessary cheaper) to form a tough wear resistance coating. In this case, pure Nitrogen gas is chemically reacted with the metal such as iron (Fe) by holding the metal in the Nitrogen gas environment at high temperature allowing the chemical reaction to take place.

The true FeN (tenifer) coating has a dull-gray color surface. Definitely, never black. In some applications, FeN coatings can also be polished to give a bright metal finish appearance."




"Melonite Processing

The MELONITE� Nitrocarburizing Process
MELONITE is a thermochemical treatment for improving surface properties of metal parts. It exhibits predictable and repeatable results in the treating of low and medium carbon steels, alloy steels, stainless and austenitic steels, tool and die steels, cast and sintered iron.
Melonite Processing : Salt� Bath Nitriding System
As the first job shop on the west coast to offer Melonite processing, Burlington uses its salt bath experience to diversify its servicing to the Southern California metal finishing industry. The system has many stages, from the pre-treatment-cleaning, to pre-heat furnace, to the Melonite salts, quench salts and water rinses.
Melonite Processing: Melonite QPQ
Melonite� and Melonite QPQ� are thermochemical processes intended for the case hardening of iron based metals. These processes are categorized as molten salt bath ferritic nitrocarburizing. During these processes, nitrogen, carbon, and small amounts of oxygen are diffused into the surface of the steel, creating an epsilon iron nitride layer ( - FexN).
A degraded form of this nitride layer (gamma prime: ' - Fe4N) is obtained during plasma or gas nitriding. The nitride layer is composed of two principle zones. Zone 1, called the compound or "white" layer, extends to a case depth of ~0.0004" to 0.0008". The compound layer is porous, which lends to the lubricity of the finish, and hard (~700HV to 1600HV). Zone 2, called the diffusion zone, extends to a case depth of ~.004" to 0.008".
In addition, small quantities of substrate carbon are pulled from deeper within the substrate toward the surface. The diffusion zone demonstrates a decreasing gradient concentration of carbon and particularly nitrogen as the gradient extends deeper into the surface of the substrate. This property yields a tough outer surface or shell, yet alloys the material to retain ductility, thereby lending to the overall strength of the material.
Resulting properties from these chemical and structural composition changes are increased surface hardness, lower coefficient of friction, enhanced surface lubricity, improved running wear performance, increased sliding wear resistance, and enhanced corrosion resistance. Naturally, the alloy of the substrate will influence which properties are principally affected and to what extent they are affected. The following chart demonstrates what properties are best enhanced by varying the Melonite process:
Melonite Processing: Melonite Q
� Improved Wear Resistance
� Improved Running Properties
� Increased Fatigue and Rolling Fatigue Strengths
� Heat Resistance
� Black Color
Melonite Processing: Melonite QP
� lncludes the properties of Melonite Q
� Lower coefficient of Friction
� Decreased surface roughness
Melonite Processing: Melonite QPQ
� lncludes the properties of Melonite Q and QP
� Low Light Reflection
� Further Decreased Coefficient of Friction
� Enhanced Corrosion Resistance (Not suitable for stainless)
"

greentimber,
Read this. I didn't google, copy and paste this below.


Butch,

You may find this interesting.

I was the Armorer for the Army Reserve Shooting Team for over a decade so I do have quite a bit of experience with both processes.

As I am sure you know, most G.I. barrels are made from chrome molly steel which is more susceptible to corrosion than stainless steel. Chrome lining is used on G.I. bores both to extend their shooting life and to protect them from corrosion that can be a problem in battlefield conditions where maintenance is sometimes sporadic or insufficient. Chrome lining does a pretty good job of protecting battlefield weapons. One of the objections to chrome lining is that it is thought to decrease accuracy. This seems to be a valid criticism and is backed up by machine rest tests I have conducted of identical barrels (same manufacturer but half chrome lined and half not).

As you are aware most barrel "wear" is in the throat area. So eventually the hot gasses from the burning of the gunpowder will eat thru the chrome lining at the throat. It is rumored that at this point accuracy will plummet but I have not found that to be true. (Or if true, it is overstated or maybe only occurs for that short period when there is both chrome and bare steel in the throat simultaneously - just at the point of initial break thru.) Chrome lined barrels can continue to shoot well for thousands of rounds after the bare barrel steel at the back of the barrel (throat) has been exposed due to erosion of the chrome lining. Another criticism of chrome lining is that it can flake off later in the life of the barrel resulting in poor accuracy. Obviously, this could also cause maintenance problems if the user is depending on the chrome to ward off corrosion and thus is careless in his bore cleaning. If corrosion is allowed to occur pitting will result and that will ruin accuracy for sure.

Barrel pitting was one of the reasons I got involved in Salt Bath Nitriding. I was loosing nearly as many expensive match grade barrels to improper maintenance (causing pitting) as I was to wear out. This was under the relatively benign target shooting conditions. Obviously given the reputation of degraded accuracy, using chrome lining wasn't an option. So for the past couple of years I have been Salt Bath Nitriding all of my match barrels and haven't had a single one exhibit any pitting. During that 2 yr. period shooters have put anywhere from a few hundred rounds to thousands of rounds on said barrels. I don't know how long the coating will persist so at this point I am still evaluating it as a preservative. I don't know what will happen in another year or two when these barrels get more wear on them. Salt Bath Nitriding goes on both inside of the bore and on the outside surface. So, instead of 2 manufacturing steps you have combined them into one. Salt Bath Nitriding doesn't degrade accuracy one iota, unlike chrome lining. This was the first thing that I verified when I began using the process. I broke in a bunch of barrels and then machine rest tested them for group. I recorded and kept the targets, cleaned up the barrels, and sent them to MMi TruTec for the Isonite process. When they came back I reassembled them on the same receivers with the same torque settings, same bolt carrier assemblies, same flash suppressors, etc. Then they were retested with the same ammo lots. NO degradation in accuracy and about a 1% increase in muzzle velocity.

Chrome lined barrels seem to clean up rather easily after a range session. I found the ease of cleaning of Isonite coated barrels to be similar to chrome lined barrels. The Isonite barrels clean up the easiest of any non chrome lined barrels I have ever used. Isonite can be applied to either stainless or chrome molly but the factory needs to know what steel you are sending them because the application process varies a bit. Again, I only have about 2 yr. of cleaning experience with Salt Bath Nitrided barrels. I don't know if the ease of cleaning will continue as the barrels get more rounds on them. Generally speaking, most non coated barrels get harder to clean later in life. Although stainless has a reputation of being corrosion resistant it isn't corrosion proof (I have had plenty of them return pitted) so I coat both my C.M. and my SS barrels. The Isonite on the outside of the stainless barrels cuts reflection down so my shooters like it.

I mentioned flaking of chrome lining inside the bore. Joel Kendrick is my contact at MMi TruTec, the company in Arkansas that does my Salt Bath Nitriding (they call it Isonite). He was mentioning using the Salt Bath Nitriding inside the bore prior to chrome lining it to get a better adhesion. He is currently working with one of the military contractors (maybe F.N., but don't quote me on that) relative to this process. He has given me permission to give out his contact information so I have cc'd him in my reply to you. He can give you the specifics of any testing and evaluation that has been done relative to this process and can give you quotes, etc. should you just be interested in the Isonite by itself as I use it.

One last quick note on chrome lining. Such barrels have the reputation of changing point of impact when heated up. I have found this to be very true. It may be due to the way the different metals (chrome molly and chrome) expand inside the bore. What ever the reason, it does happen and, again, this was verified on a state of the art machine rest. Isonite doesn't exhibit this characteristic.

I am sure you are well aware of some of the things I covered. Lacking specific questions, I just sort of used a shotgun approach which ended up being fairly long. If I left anything unanswered please feel free to get back to me. I have enabled my Spam Blocker to allow your e-mails to come in with out the automated hate responses that Earth Link sends out. I am sure Joel would also be glad to clarify the technical aspects of the Salt Bath Nitriding process. So far I am very pleased with it.

Best of luck!


Joe Carlos

Joe, I appreciate your post. I also have personal professional experience with the process in a number of firearms related applications spanning several years, the details of which I can't disclose. To provide a general summary, I have seen numerous and repeated problems as a result of the nitride process as applied by more than one of the top names in the business.

My point in this is that, while I REALLY want the process to be dependable and repeatable, my first-hand observations and experience with the process has given me zero confidence that positive results (specifically accuracy in precision rifle barrels and corrosion resistance preservation in stainless) can be achieved *consistently* with it. Moreover, just this week I have held in my hands stainless steel firearms components that we're corroded by the process. There is a major firearms company that discovered this the hard way on one or more of their product lines. To the tune of lots of $$$.

I'm glad to hear positive reports from people who have used nitride successfully and want to see continued refinement in firearms applications. I would currently have no issues with nitride on a chromoly carbine barrel (the industry has seen a good deal of success in that role).

My experience with mine and several others that had theirs done as well as a couple of hunting clients that came with melonite treated rifles is that corrosion becomes virtually a non-issue. I have done all SS barrels and one CM action and bolt. Not a trace of rust on the receiver after being through several extended wet periods with no chance at maintenance.

My issue was that something occurred INSIDE the bore although borescoping it did not reveal anything to point a finger at.

Butch had it lapped for me and when I get a chance, I will likely re-install it and see if the flier problem disappeared.

Barrels can be tempered at a much higher temperature than a receiver since their ultimate yield strength does not need to be as high. I think this is the issue with 416 actions.

Several of the action makers that once uses 18-8 or similar precipitation hardened SS now use 416 for their actions. These obviously can't take the heat that the other alloys can.

did my l61 r chambered for 300 wby.. it brings the surface hardness to rockwell 70 and the action feels like it is on ball barings gives the metal a really coal black matt finish, looks really nice. warning only do new barrels of known steel quality. and dont do a gun that has been fired. my sako shoots a 200 gr ab at 3050 with 24 inch barrel and under max load. and ragged little holes. i have only used it last season on a 10 day moose hunt in bc. the finish held up really well, still looks new