doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Case Coloring Metal Prep

Doug's (PA24) work is spectacular.

Doug, will you please move that picture of the LC you colored from the Rust Bluing thread over here as an example?

Regards
Ken

If you quench much below the critical temp you will get colors but little to no surface hardness. Opinions vary and some very good craftsmen go this route. I like to have a hard outer skin for several reasons, to inhibit corrosion, to prevent wear on parts that pivot and to preserve engraving. One gentlemen I know gets great colors but little hardness and he feels that the much reduced chance of warping occurring at a lower temp and the softer surface that comes with it is far better than a damaged customer frame. He is a board member here and may comment on this thread. You can find several good threads on the ASSRA and Marlin forums as well. Interesting stuff and with the new digital controlled ovens quite a bit of guess work can be removed from the process. I would like to see some pictures of crucibles people are using as I'm unhappy with mine. I was given them by a friend but I think his design could be improved upon.

I only throw this out for consideration.

What Sam mentioned, particularly around 900*, is actually not tempering, but a process that might be called spheroidizing annealing. There are various good reasons to consider it, but two that come to my mind, the part never needs to reach critical temperature, and the exact make up of the hardened steel, that someone elects to soften, is unknown.

Because the hardened steel case is unknown, it is possible to convert that steel to a less than ideal form, distribution of the carbon, just by cooling it too slowly during annealing.

Steve, as an aside, I'm not so sure annealing can prevent over carburizing. On it's own, annealing shouldn't remove or add carbon to the steel case. I suspect if the steel skin is heated, particularly above critical, in a wood charcoal pack, presumably(?) to eliminate oxygen, there is a pretty fair chance that available carbon is driven towards the part under those conditions.

This is only discussion, and no heartburn with anyone's preferred methods. I appreciate the small look in other shops.

Marlin 1892 .32 that I did....Originally $1.00 extra for CCH frame from the factory in the 1890's, what a deal...!...Neat little gun...








A different L.C. that I did, the one above is a 12 gauge ejector, this one is a 16 gauge extractor....





Best Regards,

More food for thought.

First, thanks Doug.

Second, the dropping of the temperature before quenching is only after holding the piece above critical temperature. I've read many references about the processes that use lower temps to achieve color, but, true, it is said it results in colors but doesn't achieve true hardening. In my trials I'll experiment with the process, and since I'm associated with an industrial heat treating company with a lab, I'll be able to report if true hardening occurred. I'll also do a test at consistent low temp as well, (below critical) to see what hardness results from that process.

Is packing in charcoal for annealing really necessary? That's the real question.

I agree, the thread on the Marlin site is great, and is probably the most comprehensive thread about CC info on the Net.

Packing in charcoal for annealing provides an oxygen free environment to prevent scaling. There are other methods. It can be done in an inert gas oven and some people use a steel wrap especially made for this. I've tried the wrap and do not care for it. I have had things hardened in a gas furnace but never annealed. I always anneal and feel it is a very necessary part of the process.

OK, makes sense. Now, what about the post-coloring stress relief heat? I'm guessing that it also requires a charcoal pack to prevent scaling.

This I fully believe. Aside from some machining/engraving, I was just wondering, why.

You had an earlier crucible question, I thought I'd pass along comments on a short tv demo that Connecticut Shotgun did on their case coloring process. They used a round crucible that looked to be 5" inner diameter by about 6 to 7" deep. Pretty heavy gauge with formed raised rings around the outside so that a non clamping 'U' fork style holder wouldn't slide up or down on the crucible.

It had a slip fit, but fairly close looking fitting cover. They put a quick, medium tan colored, refractory cement coating around the seam of the cover. The base of the crucible had legs on it, at least a 1/2" maybe a bit more, probably so it would heat up more evenly.

Separately from the crucible, their process was, a claimed wood, cow and chicken bone, and leather charcoal. The camera man zoomed in on a 1332* kiln setting with the temp reading 1331* when the pack went in the oven. It stayed in a claimed 2 1/2 hrs. It seemed to take about 10 seconds before the part was quenched. When everything was inverted over the quench tank, the cover stayed on and took a couple light taps with a small hammer, standing by, to release the cover and everything else into the quench. They wired the receiver to a tab on the inside of the crucible, so it couldn't drop down into the container, but it dangled probably a couple of inches in the quench. There was no comment about the quench or how it was prepped.

It appeared to be a credible demonstration on a real A10 receiver, that they made it appear like the same receiver was shown on a finished gun. I've used a welded up pipe crucible with cobbled up similar to the above, but quite a bit smaller. I just thought there might be some interest in a technique that was shown, but maybe not widely known.

I also appreciate that you commented about the true hardness of safe, sound, real world gun receivers. And, the preference for hardened wear surfaces, but the reality that it may not always be so.

Maybe Ken, a little caution here. I have seen case colors start muddying and fading by about 350*. Your colors may stand up to higher heat, but in all likelihood at temps that're quite a bit below the ability to scale steel.

"What Sam mentioned, particularly around 900*, is actually not tempering, but a process that might be called spheroidizing annealing."

Craig, you are right there. Engravers are only interested in getting the metal drawn back to a level easily engraved. If too soft it will ding too easily making for a lot of minor cleanup/polishing during the project.