doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com case colors vs. hardening?

This may have ben addressed previously, but I was reading Hamilton Bowens book and if I understood correctly The wonderful colors produced by heating low carbon steel in a charcoal pack crucible will not be recreated with more modern high carbon steels. Hence the cyanide bath to attempt to recreate the colors without the hard skin that isn't needed with the lower carbon. I have a late 30's Sterlingworth and if I remember my reserch they switched to cyanide for late production. Does this indicate the use of a higher carbon steel later in production?

I see many currently produced guns with case colors. Oscar had Kreighoff and an other company in his shop making films on how he produced "American Style" colors. I see his work every time I look at a case hardened Kreighoff. So my answer is modern steel can be colored in charcoal.
bill

Bill is 100% dead on ---- new modern 4140 ch. moly steels can and are color cased daily. The switch to cy. coloring/hardening was due to the lower cost. However, there are pieces out there today that are cy. colored that you can engrave thru as easily as if the steel was still raw/unworked.

Thanks for the clarification, so much to learn and so little time!

Actually, traditional color case-hardening whether by carbon pack or cyanide bath is incompatible with the heat treatment of modern through hardening alloys such as 4140. However, the traditional colors can be reproduced on those alloys by heating and quenching from lower temperatures. This is possible because all the temper colors are produced below 700° F. 4140 is typically tempered at about 1000° F after it is hardened to achieve the desired toughness and hardness ( RC 36-40) desired for guns.
Heating and quenching below 1000° have no affect on the original heat treatment yet allows full color(but not "case-hardened") developement. This also explains why Ken Hurst can engrave such pieces without annealing.

OB

Do note this is applicapable only to those mentioned alloys which are (Through) hardened, quenched & then tempered at 1000°. Re-heating an originally case hardened part to these temps will almost completely destroy the hardness of their skin.
The only chart I still have at home for 4140 is in an older Machinery's Handbook & it gives an average Rc hardness of 34 after an oil quench & then a 1000°F temper. An 800°F averages to 38Rc.
This corresponds with my recollections from many years in a machine shop where we had our own heat-treat deparment. Lower drawing temps were required to get 40Rc.
It is also noted that even if it were drawn at 1300°F & its hardness reduced to only Rc20 it would still have a tensile strength of 110K psi & a yield of 85K.

The cyanide method is fully capable of imparting carbon into a low carbon steel and producting a casehardened surface. I also beleive that the later Fox guns were still low carbon steel frames. I could be wrong.

Chuck is spot on here. The primary purpose of the Cyanide treatment was for that "Hard" skin of high carbon which had been cooked into a piece of low carbon steel via the molten Cyanide bath. The colors were secondary. This was a quicker & less expensive method than Pack Carburizing & was useful for many purposes where only a relatively thin skin was needed. By using longer times in the furnace a deeper skin could be attained by the pack carburizing process than by Cyaniding.

The cyanide process was known for a long time. It came into heavy industrial use during and after WWI. If you have ever been around a commercial facility that used bone charcoal, you quickly realize how dirty it is and how difficult it is to handle all the charcoal.

Here are a couple of early texts that talk about the process. There were several ways to implement cyanide case hardening. A molten dip, powder, placing some cyanide into the vessel and thereby use the gas method.

http://books.google.com/books?id=GT8LAAA...ing&f=false

http://books.google.com/books?pg=PA94&am...amp;output=text

Case color does not always result from for case hardening. It is the impurities that are introduced by bone or cyanide that result in the color.

Pete