Faux Color Case Hardening refinish for vaquero - Page 2

HiBC · October 26, 2023, 01:29 AM

We are getting past my pay grade. I don't know what I'm talking about...

But 8620 alloy steel is good for investment casting. (What Ruger is good at)

It can be case hardened but they put something in the alloy that decreases possibility of embrittlement.

It walked off somewhere,but I used to have a Jorgensen Steel supplier handbook of alloy and tool steels. Light reading!

Oliver Sudden · October 26, 2023, 09:19 AM

8620 was made for case hardening and is generally used that way. I’m told Ruger uses 4140 for their investment cast frames.

**Unclenick** · October 26, 2023, 03:36 PM

Case hardening at the industrial level is done in a carburizing atmosphere. Carbon monoxide is one, but they mix in other things to improve the speed of carbon diffusion into the steel. You might think charcoal or some other form of pure carbon would be a good idea, but it actually is very slow to diffuse into the steel when it is pure; it needs transport. The oxygen in carbon monoxide is apparently reactive enough to glom onto the steel and let the carbon diffuse in. The diffusing carbon then donates its oxygen atom to another carbon monoxide molecule to become CO₂, which, having a higher molecular weight than CO, then sinks to the bottom of the carburizing oven, where it can be bled off.

This link shows a huge object with a 1/4" deep case. Enough heat in a carburizing atmosphere for a long enough time is mainly what you need to accomplish that, but Kasenit and that sort of thing heated briefly with a torch might get 0.002-0.005" deep or so, depending on the steel. Case depth is all about time, temperature, and the source of the carbon. Traditional color case hardening used horn and hoof and leather scraps, the latter being wound in strips around the steel to produce a particular pattern. Some bone meal and other such stuff were used for packing, too, but the organic materials apparently do better about carbon donation, and thus were the important elements.

The colors are caused by oxides, and while they don't fade in the sun, neither are the oxide layers deep, so they wear off the same as bluing does.

Usually, the reason to use case hardening is to combine an elastic, crack-resistant core with a hard, wear-resistant surface. During the transition of the Springfield '03 from eyeballed tempered steel to nickel steel, for a brief period (something in the range of a million receivers, maybe, but don't quote me on that; look it up instead), they used double-heat treated case hardened steel. This process takes advantage of the fact very high-carbon steel has a lower austenitic temperature than mild steel, so it will quench hard at a lower temperature. This allows the part to be carburized at the mild steel quench point (usually around 1600°F), quenched so everything is hard, then reheated to around 1300°F to anneal the core and quenched again. The 1300°F temperature hardens the carburized case file-hard. It would then be heated to around 350°, IIRC, to prevent the case from stress cracking. The result of this "double-heat treatment" process was a strong, non-cracking part with a glass-hard surface. By all reports, these were the smoothest operating Springfield actions ever made.

Hatcher's notebook has the process details, should anyone be tempted to pursue this sort of work. However, I think for color case hardening, in order to preserve the oxide pattern, the steel is simply reduced directly to the quenching temperature of the outer case before quenching, as old guns didn't require any temper to remain in the core steel. But, again, don't quote me on that. Research it yourself.

Oliver Sudden · October 27, 2023, 11:52 AM

Quote:

Originally Posted by jackmoser65

I guess it's news to you that you can't case harden Ruger's through-hardened cast frames without embrittlement? Turnbull kinda went to a lot of trouble to figure out how to put proper colors on them without making them brittle.

Knowing the complete process is important before doing any work. Annealing the steel is step one.

jackmoser65 · October 27, 2023, 11:29 PM

Why would Turnbull need to develop a new process if all they had to do is anneal frames first?

Schlitz 45 · October 28, 2023, 06:34 AM

I’d done a lot of black powder builds & was looking for something more visually interesting than blue or plumb brown for a project. This is how the no heat “case hardened” looks.

October 26, 2023, 03:36 PM	#28
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Case hardening at the industrial level is done in a carburizing atmosphere. Carbon monoxide is one, but they mix in other things to improve the speed of carbon diffusion into the steel. You might think charcoal or some other form of pure carbon would be a good idea, but it actually is very slow to diffuse into the steel when it is pure; it needs transport. The oxygen in carbon monoxide is apparently reactive enough to glom onto the steel and let the carbon diffuse in. The diffusing carbon then donates its oxygen atom to another carbon monoxide molecule to become CO₂, which, having a higher molecular weight than CO, then sinks to the bottom of the carburizing oven, where it can be bled off. This link shows a huge object with a 1/4" deep case. Enough heat in a carburizing atmosphere for a long enough time is mainly what you need to accomplish that, but Kasenit and that sort of thing heated briefly with a torch might get 0.002-0.005" deep or so, depending on the steel. Case depth is all about time, temperature, and the source of the carbon. Traditional color case hardening used horn and hoof and leather scraps, the latter being wound in strips around the steel to produce a particular pattern. Some bone meal and other such stuff were used for packing, too, but the organic materials apparently do better about carbon donation, and thus were the important elements. The colors are caused by oxides, and while they don't fade in the sun, neither are the oxide layers deep, so they wear off the same as bluing does. Usually, the reason to use case hardening is to combine an elastic, crack-resistant core with a hard, wear-resistant surface. During the transition of the Springfield '03 from eyeballed tempered steel to nickel steel, for a brief period (something in the range of a million receivers, maybe, but don't quote me on that; look it up instead), they used double-heat treated case hardened steel. This process takes advantage of the fact very high-carbon steel has a lower austenitic temperature than mild steel, so it will quench hard at a lower temperature. This allows the part to be carburized at the mild steel quench point (usually around 1600°F), quenched so everything is hard, then reheated to around 1300°F to anneal the core and quenched again. The 1300°F temperature hardens the carburized case file-hard. It would then be heated to around 350°, IIRC, to prevent the case from stress cracking. The result of this "double-heat treatment" process was a strong, non-cracking part with a glass-hard surface. By all reports, these were the smoothest operating Springfield actions ever made. Hatcher's notebook has the process details, should anyone be tempted to pursue this sort of work. However, I think for color case hardening, in order to preserve the oxide pattern, the steel is simply reduced directly to the quenching temperature of the outer case before quenching, as old guns didn't require any temper to remain in the core steel. But, again, don't quote me on that. Research it yourself. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

October 26, 2023, 01:29 AM	#26
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,289	We are getting past my pay grade. I don't know what I'm talking about... But 8620 alloy steel is good for investment casting. (What Ruger is good at) It can be case hardened but they put something in the alloy that decreases possibility of embrittlement. It walked off somewhere,but I used to have a Jorgensen Steel supplier handbook of alloy and tool steels. Light reading!

October 26, 2023, 09:19 AM	#27
Oliver Sudden Senior Member Join Date: January 7, 2017 Location: Colorado Posts: 272	8620 was made for case hardening and is generally used that way. I’m told Ruger uses 4140 for their investment cast frames.

October 27, 2023, 11:29 PM	#30
jackmoser65 Senior Member Join Date: October 11, 2014 Posts: 754	Why would Turnbull need to develop a new process if all they had to do is anneal frames first?

October 28, 2023, 06:34 AM	#31
Schlitz 45 Senior Member Join Date: January 14, 2018 Location: Colorado Posts: 385	I’d done a lot of black powder builds & was looking for something more visually interesting than blue or plumb brown for a project. This is how the no heat “case hardened” looks.