Custom CZ 75 - Color Case Hardened Frame

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dakota.potts

New member
A project I worked on in school recently. Wanted to customize my CZ 75 BD as I never really shot it after I got my P-01. I stripped everything, started a trigger and action job, etc. and got to refinishing. My plan was to hot blue everything, but it was suggested to me to consider color case hardening and that was an idea I really liked.

I started by machining supports for the gun to hold heat in (better color) and keep it from warping. I found a long, thin piece of scrap metal laying around the shop which I cut slots into to fit the internal slide rail. I also drilled and tapped it for a set screw.

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I turned a plug on the lathe to fit the recoil guide rod recess.

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I also milled a block to go through the magazine well and drilled it for a cross pin blank to hold it in place. This ended up actually getting a much better color than the frame (no pictures though) because of its solid mass and, I believe, high carbon content.

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So I packed it in a crucible with charcoal and graphite, heated it in a furnace at 1440 degrees for an hour, and quenched it.

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Colors could have been brighter, but overall I'm happy with it. Especially for my first time trying this color case hardening process. I think a couple factors led to the loss of color, but I won't get into that unless someone's interested in the technical details.

The rest of the gun will be done in the next week or so so I'll post pictures of the full project. Video will also be coming soon, including the video of the impressive smoke/spark blast that quenching it produces.
 
A couple contributing things

Heat could probably be brought down 50-75 degrees
Charcoal used could have been of better quality than what was available at the school
The lid to the crucible got stuck when dumping and took a minute to remove, I'm sure that I lost some color during that time. That is shown in the video.
I got an incomplete drop to water and the exposure to oxygen might have allowed some of the color to creep back to grey.
Metal quality could be a factor
Machining more small blocks to fill gaps in the gun more thoroughly might have held heat in better.

All that said, the mag well block came out with beautiful color so I just have to figure out how to bring smaller parts to that same level of color since it worked for the thick block of steel.

Also, some of the colors are more obvious in person
 
Video up. Sorry if the music is loud, just put something royalty free over the top to fill up the space.

The nice ash "explosion" happens a little after 2:30 if you don't want to watch the whole thing. You can see how the lid to the crucible got stuck in place. I'd never tried this before but will try to stay away from this crucible design in the future. It actually took a whole team of students to get this done as you can see.

https://www.youtube.com/watch?v=KQ2wGcCabQs&feature=youtu.be

If I pursue this further in my own shop in the future, it will be with a smaller furnace and crucible that one person can safely handle. That might limit me to small frames/receivers, and small accessories like scope rings and sling swivels, but I definitely want to experiment with this field further.
 
Are you able to post a pix of the magwell block after? I will say, you did lose a good amount of time with the stuck lid.

Interesting that the magwell block came out in a different way? Maybe the content of the metals is different enough to create the different effect?
 
I left my magazine block in my toolbox at school because I figure I can use it as a vise block in the future -- but I will post up a picture of it when I get back to school in a couple days. It really had some vibrant colors with a deep yellow hue and some wonder blue swirls. So the lid being stuck didn't seem to affect that part.

I believe that because the metal was a solid, squared block of steel it was better to hold heat and had more consistent surface area for carburization and oxidation to take hold. It was a little hard to cut on the mill as well, so it might have had a higher carbon content. Hard to know, really. I definitely want to experiment with this process more, as aside from the basics there's a lot of alchemy and superstition on the internet about it.
 
The color keeps developing slowly and I'm not sure what to think about it. I check it daily for rust and it seems elements of color are slowly creeping across the grey. I'm now seeing washes of copper, rose gold, purple, and electric blue that appears almost as an incandescent two tone effect under the slate grey in some areas. Color around the magazine well, with more of the traditional pattern I was going for, seems more stable.

Not really sure what to think at this point except that it's surely unique and it's still not done surprising me.

Not confident I could photograph any of the colors I'm seeing though.
 
For whoever wanted to see the magazine block colors:

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My phone washed out some of the yellows in favors of the blue, but you can still see the bright colors achieved. I think this has to do with the thickness of the block versus the relatively thin metal of the frame.
 
Started rust bluing the slide today. I don't know what steel the 75 frame is made from, but it shows incredible resistance to rust. Laurel Mountain Barrel Brown and Degreaser did nothing to the metal until I heated it slightly and it left a bright copper color that looked like a penny. Spent hours trying to get it to rust properly and couldn't.

Things went better when I switched to Birchwood Casey Plum Brown. I did get to boiling and carding today and it is turning a nice blue color... couple more passes and it should have some nice depth.

Also will be nitre bluing a lot of the control parts and screws. Should be ready to re-assemble by the end of tomorrow.

Don't know if I'll start a new thread or not but I'll update either way.
 
Nearly there today. Hot blued the slide (change of plans from rust blue) and nitre blued some of the small parts.

Still likely going to go in and re-heat the slide stop to the same blue as the others. It was the first piece I did before I got the hang of the bright blue.

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Is nitre bluing similar to cold bluing? If so, it may not be durable enough for controls that get a lot of contact. (Or you'll just have to redo them from time to time...)
 
There is a chance of what you're talking about.

At just under 600 degrees for a blue color, it is in the heat range that will begin to affect hardening. It is at that temperature for maybe 30 seconds before a cold quench which should retain a good amount of the heat. I am not a well educated metallurgist, though, so a lot of it is "maybes" and "should be"s. I will continue keeping an eye on the slide stop and other affected parts for any accelerated or undue wear.

For anybody who might get the idea to try the same processes that I have done, it is good to note that any finish applied by manipulating heat has the potential to affect the heat treat of parts. Hence, don't nitre blue any critical pressure-bearing parts (bolt face, receiver, barrel, lugs etc.)

EDIT: Sorry Walt, don't see your original comment any more about the heat treatment of the small parts.

Nitre bluing is not a very durable finish, maybe less so than cold bluing. As a whole, this gun will need more maintenance than needed before. My newer model CZ (P-01) has taken over all of my serious heavy use and I never shot the 75 anymore so I decided to experiment with some finer finishing techniques on it and tune it a little for range use only. I'm no Doug Turnbull, but I wanted the experience of re-finishing a service pistol like this. Absolute worst case scenario, it seems, is replacing any failed parts, bead blasting, and a basic refinish (blue, epoxy-based paint, etc.)
 
Others reading your response to my original (but quickly changed) comments are probably wondering what in heck is going on. Sorry... My fault.

After re-reading your comments (and editing my long response, which was concerned about HOW the heat involved in case hardening and hot bluing might affect part hardness), I realized that you were nitre-bluing the small pieces, and it was only the slide stop that had me concerned.

Get that piece too hard (or the hardening too deep), and it might break more easily, and CZ slide stops, while not fragile, do break, The stored force of the slide slamming forward and pushing a relatively small barrel lug against the slide-stop cross member could lead to some interesting consequences. Nitre bluing might not be an issue, but it might not stay pretty, either.

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I'm not going to advocate for others to try the same on their pistols without a lot of thought and knowledge. I am in the last part of my schooling where I have the most freedom to experiment and where I have access to most resources if I make a mistake... in other words, now is the time to try things for me and probably the best time for a mistake to be made if there is one.

It's my understanding that a heat level in the 570 degree range is not enough to break down the structure of the metal to begin hardening it, instead having a slight annealing effect. With the short exposure times involved (just enough for the oxide to form on the outside of the steel) I'm not too worried about it. If anything, an annealing effect would make the steel less likely to crack or shear but may create concerns about peening or warping. This is as I was told when I got permission to do the project.

As far as not staying pretty long, it is a possibility. It can be re-done by simply polishing, heating the salts back to temperature and dipping for less than a minute. I may experiment with varnish or other sealant to protect the color and the surface of the metal for longer.
 
I found this in a GOOGLE SEARCH, after somebody on another forum complained that a company that does case-hardening wouldn't do his CZ -- with no explanation.

With many of the examples you can find of semi-autos, the slide and frame don't always seem tomatch. But, it can turn out pretty well... :)

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I looked at several of those pictures when I was preparing to do mine. I wish I had been able to achieve the depth of color in the picture above. I am happy with my gun as a very unique piece - but I believe I will continue chasing the secrets of really deep, vibrant case hardening.
 
There's a guy on http://www.czfirearms.us forum, usually in the gunsmithing sub-forum, that buys surplus CZ's and refinishes them. I have seen pictures of his work and it's really nice. His rust blue is beautiful, and he not shy about helping and detailing how he achieves his finishes. Probably you can just ask a question and he'll answer, seems like a nice guy.
 
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