doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Case Coloring

I believe that CSMC RBLs are made of 4140 and many of them are colored, but I couldn't say how.

Cyanide is not an element, but rather a compound which consists of a carbon atom triple-bonded to a nitrogen atom. As others have stated above, it is the carbon which bonds to the iron. Think of it this way. The iron forms a set of boxes all bonded to each other. Given the right conditions, a carbon atom "slips" into the box. This has the effect of producing a "harder" metal. The key is to prevent the iron atoms from bonding with oxygen during this process. If they do, all you have done is to produce rust. That is why, using charcoal or cyanide, the pack and quench are so important.

If I recall correctly, when Dr Gaddy took SEM images of a case color harden piece, the depth was only a few atoms.

Pete

Last year Connecticut Shotgun let one of the shooting TV shows do a segment on how they get their case colors. Kind of a generic presentation with not a whole lot of info, but the camera clearly showed the oven set to 1331*. I don't know if that had any significance, but if the parts were quenched at that temp, there would not likely be any ability to harden the surface or otherwise. The demo was on an over under receiver and it seemed to come out with the right look.

Note that an un-heatreated piece of 4140 will be both harder & stronger than a piece of 1018. The 4140 has even far greater potential through proper heat-treating & tempering. I don't really recall the hardnes/Temper range for it, but seriously doubt a piece heated to over 1200�F will retain a hardness of Rockwell 40C. That it is strong enough for the mentioned uses is obvious for a piece of case-hardened 1018 was adequately strong. That 4140 will work for these conditions is simply testimony to its great versatility, but I can tell you for certain if Faux Colored parts were its major use it would be an extremely short time before it would be no-existent as an available alloy. Its greatest use is for high strength, heat-treated parts which does not include tempering it to 1200+�F.

The cost to do cyanide, versus charcoal pack, case hardening must not be much different for a small gunshop today. Ron's, in Oshkosh, WI, does both, and the cost is only $10 difference for a doublegun receiver.

SRH

2-piper I do not dispute your points. You have most likely forgotten more about this than I have learned. But if the goal is to color alone is that not done at the lower temp.? Hardness is already inherent in the metal. The color is all that is needed with 4140. Other milder, softer metal could be hardened by longer time exposure at a higher temp. for what I understand from my notes. I doubt H&R used only 4140 steel in making all those single shot guns. I suspect they used an easier to work metal and then hardened it with a case color change as a minor side effect.

Stan posted,

Stan, the process costs themselves wouldn't be much different, cyanide is cheap enough, but there are environmental and safety considerations that would add greatly to the expense.

Safe storage, personal protection equipment, poisoning recovery kit, proper signage, and treatment of contaminated waste waters are all statutory requirements in UK, and from what I saw of cyanide handling in the US would be the same there.

Hazarding a guess, I'd put the factory cost ratio of cyanide to charcoal at around 15: 1. How that translates into the final invoice is up to the individual gunsmith, but his operating costs will be much greater with CN.

Eug

molloy: then there are the funeral expenses to consider...

From the ASM Heat Treater's Guide

SAE 4140 Steel Tempering
Tempering
Temperature Hardness
Brinell Hardness
Rockwell Tensile
400�F 200�C 514 HB 55 HRc 297 KSI
500�F 260�C 477 HB 50 HRc 243 KSI
550�F 290�C 461 HB 48 HRc 235 KSI
600�F 320�C 444 HB 47 HRc 225 KSI
650�F 340�C 429 HB 46 HRc 217 KSI
700�F 370�C 415 HB 44 HRc 210 KSI
800�F 430�C 363 HB 39 HRc 182 KSI
900�F 480�C 331 HB 36 HRc 166 KSI
1000�F 540�C 293 HB 31 HRc 145 KSI
Data extrapolated from a hardness graph given in Brinell with nearest points taken from a conversion table for Rockwell hardness. Temperature conversion to Celcius rounded to nearest 10�. Tensile not specifically for 4140. All data +/- 10%

To add some perspective to the data above...my experience suggests that many modern firearms that are made from 4140 are hardened and tempered to around the low to mid 30's HRC (hardness) giving an ultimate tensile strength from about 145,000 psi to 165,000 psi. Mild steel has an ultimate tensile strength of about 64,000 psi. Case hardening is in the order of .003-.007" and does not change the core strength. Yield strength numbers are lower for both.