Metal Finishes and Treatments, Part 2: Melonite and Spray-On Finishes

In the last installment, I talked about the importance of heat treating and anodizing as they relate to AR-15s. The same basic concepts apply elsewhere, too. As before, I consulted experts wherever possible – but if there are any errors, they’re my fault.

Today, I’ll briefly (okay, not so briefly) discuss two finishes that you might find on an AR, but are more likely to encounter on a handgun: Melonite and spray-on finishes. The latter generally contain the word “Kote” or “Cera” in their name. Or both.

Melonite/Tenifer/Nitriding/Nitrocarburization/QPQ

Known by a variety of terms, this process involves a lot of heat and some interesting chemistry. It can be applied to a variety of steels. There are varying levels of the process, which is broken down into segments called “Quench, Polish, Quench” (hence, “QPQ”).

While many of the claims arising from and most of the mystique surrounding Melonite relate(s) to the performance of the full QPQ process, it’s possible for only the first “Q” to be done, and stainless steels don’t receive the full corrosion resistance benefits of QPQ. This means that QPQ’d stainless steel will have less corrosion resistance than QPQ’d carbon steel. But I’m getting ahead of myself…

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.”

You’ll often hear people refer to items being “coated” or “plated” with various processes, with “coated” being the more popular term. In this case, though, it’s a big misnomer. Melonite is more correctly referred to as a “treatment.” It’s not sprayed on like a coating, and it doesn’t build up on the surface of the metal like a plating. If you want more details on the process, click the link above. I won’t bother paraphrasing further. I’d rather concentrate on what Melonite does.

Melonite offers excellent corrosion resistance, high surface hardness, and increased wear resistance. This does not necessarily mean that it will never show signs of cosmetic wear, or that it will never rust. Even if the process is completed correctly (there have been many instances of improper Melonite treatments, especially on some newer production handguns), rust can and will occur. For example, I have had rust form on a number of Glock slides, which are treated with Tenifer, Glock’s version of the process. This rust occurred in the course of normal carry in under one day.

Most people, though, will never see rust on a “Melonited” surface, even in extreme conditions.

As for surface hardness, the number which is generally thrown about is 70 on the Rockwell “C” scale. This is far higher than the 28 or so which most AR-15 barrels are hardened to, at least on the outside – quality carbine barrels are generally hard chromed, which has a higher hardness – but that’s a topic for another day. What does this mean for the end user? Well, the exterior finish is going to be much less susceptible to cosmetic damage from rough handling.

Wear resistance? Well, I’ve heard many things, but still have yet to see some sort of scientific study. Still, when one hears so many positive stories from respected sources, doubt begins to disappear. One highly respected AR expert (and manufacturer) is said to have fired over 50,000 rounds through a nitrided barrel without any signs of excessive wear or that the barrel is anywhere near “shot out.” POF reports that they have seen barrels with over 40,000 rounds through them that do not need replacement.

“This sounds great!” you say. “Sign me up! I want my barrel to have this coating -er, treatment!”

Not so fast. Due to the extreme temperatures involved, many parts that have already been heat treated or assembled may not be suitable for nitriding.

AR-15 barrels, for example, should not be nitrided once assembled, because the differences in material between the barrel extension and the barrel result in dimensional changes that can cause the barrel extension to come loose. 1911s with tightly fitted components have come out of the process with parts that are either loose or impossibly tight in relation to one another – and due to the high surface hardness, fitting is very difficult. Not impossible – just very difficult.

However, if you can find nitrided components from a reputable manufacturer, you will likely be very happy with their performance. Why do I specify a “reputable” manufacturer? Because many companies that sell ARs latched on to nitriding as a cheap and easy way to sell parts as being durable and desirable – not knowing that nitriding already heat treated bolt carriers would cause them to anneal (and crack under use), or that nitriding assembled barrels would cause them to come apart after mild use.

Stay away from companies that expect you to do the final testing on their products. Ask them how their nitriding is done, and what quality control procedures they have in place to ensure that the process was done right.

“Kotes”

Gunkote, KG Kote, Duracoat, Cerakote, Cera-Hide. Are they all basically the same, like the various “forms” of nitriding? Actually, they aren’t – and the discussion of how they differ can be a bit of a heated subject (especially when Cera-Plate is involved). I’ll try to stay away from that as much as I can, but here’s a test sheet from an independent lab. It’s a comparison between Cerakote, Gunkote and Duracoat, and shows performance in various wear and corrosion tests. Lest you think that the test was biased, the company is willing to provide “test panels” to any third party lab for a comparison with other finishes.

What you need to remember with each of these finishes is that they are all essentially high tech spray paints. They offer good to great corrosion resistance, in part because properly applied “kotes” act as a physical barrier between the metal of the firearm and whatever corrosive agent is attacking it. However, they don’t offer increased surface hardness, and while they are fairly wear resistant, even the best of them don’t stack up to finishes like nitriding, hard chrome, or properly applied electroless nickel (and its various derivatives).

Like nitriding, the quality of the results depends on who did the work. I once had a rifle and a pistol “Gunkoted” – the work was over budget, far past the stated deadline, and of poor quality. The individual chose to completely remove all the anodizing on the pistol frame before spraying the Gunkote – within 1000 rounds, the “Kote” was completely gone from the frame rails, and bare aluminum exposed.

I have heard similar reports from AR manufacturers – that anodized receivers were completely stripped via media blasting, and certain high wear areas deteriorated rapidly under hard use, even with Cerakote (which seems to be one of the better “Kotes”) on the receiver. As a result, they started requiring that all such areas be masked off prior to the beginning of the prep work.

If it sounds like I’m bashing the “Kotes” – I’m not trying to. I am trying to be realistic as to their capabilities. Not every component needs a Rockwell rating of 70 or higher. “Kotes” are a great option when corrosion resistance is needed, but surface hardness and extreme wear resistance is not.

They’re also great for making a worn pistol look new again, turning a stainless rifle barrel into a less-observable color, or matching various components – one company’s polymer components in “flat dark earth” won’t match another company’s. But painting the whole thing will make everything match (if that’s your bag).

In addition, they’re pretty affordable. While hard chrome is often regarded as one of the “ultimate” finishes for a carry gun, along with NP3 (and now “NP3 Plus”), complete handgun refinish jobs can often cost upwards of $300, whereas companies such as Cerakoter.com offer complete handgun packages for as low as $110.

I had most of one of my 1911s refinished by Cerakoter, and I’m very pleased with the results – yes, it’s showing wear with use. But the slide, barrel, and other parts haven’t shown any signs of corrosion (nor has the electroless nickel plated frame, which I did myself). Corrosion was my major concern – and was a major problem when the pistol had its stock finish. In fact, Kimber’s barrels are “in the white” carbon steel – I shouldn’t have to go into too much detail about how that ended with horrible amounts of rust. I’ll have a full writeup on the Cerakoted 1911 soon.

Part 3?

So, what’s next? Well, I want to cover hard chrome, electroless nickel (and similar platings), manganese phosphate, bluing, and a few others. I’m lucky to have a number of extremely knowledgeable people reading my blog, so if I’ve gotten anything wrong so far, they’ll let me know – and I’ll post a correction.

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5 Comments

Filed under Technical Issues/Notes

5 responses to “Metal Finishes and Treatments, Part 2: Melonite and Spray-On Finishes

  1. willardcw4

    Good writeup! Didn’t realize that melonite was a treatment to the steel as opposed to a coating..!

  2. kLewis

    Great series! This is really important information.

  3. Mike

    Does anyone know where can I get a properly Melonited AR-15 barrel without having to buy an entire gun or upper?

  4. MarkM

    The comment on someone removing anodizing to coat a firearm is an interesting check point on their expertise.

    The chemical bath deposition of military grade anodizing was the best answer for protecting aluminum in the day, and little else does better for the price. As a “primer” for the aluminum, it’s recommended.

    When a refinishing “expert” goes to the effort to remove that coating just to apply a lesser one, bells should go off. Unfortunately, most don’t know that.

    The refinisher who plans to remove anodizing by grinding or sandpapering the finish should stop right there and think about it. Will the new finish be tougher than that? If it’s a coating, no, because it has to stick to bare aluminum before it corrodes, which it rapidly does in air. Finish coats adhere best to a metal prep that is locked in closely to the metal, and anodizing does that as a chemical bath application.

    Sorry for your situation, as you noted, any refinisher who strips anodizing doesn’t have a clue what they are up to. The results are usually worse.

  5. Chris

    I’m interested in your future bluing adventures. I refinished some rough spots on a pistol with some over-the-counter kit and while it looks great, it has an infamous odor that accompanies it that I am attempting to remove. One guy claimed he had do so by soaking the refinished parts in motor oil for a few days so I might give that a go.

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