doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com cyanide case hardening of shotgun parts

Drew;
I served my apprenticeship in an Air Force installation (AEDC, Tullahoma TN) which had their own metallurgical lab. During my time there I made quite a few of those little tensile pieces to be pulled apart.

Craig;
Note in the figures I gave above the % of the yield to the ultimate does tend to decrease as the steel gets harder. If one went to still higher carbon %age the tendency would be more pronounced. In the case of the case hardened 1020 the yield vs tensile would be much closer together in the case than the core.

Note that Drew's chart shows 1020 as having a tensile strength of 60K psi @ Rockwell B68. On the case hardened 1020 a tensile of 80K psi is shown. No hardness given, only that it was drawn to 400�F. This would give a quite hard case. Rockwell B68 is about the equivalent of Brinell 121 when tested with the standard 10mm diameter ball @ 3,000 KG load. This is quite soft & is basically off the Rockwell C scale which is normally used for heat treated steel. From these two figures we see the case hardening gives an increase in tensile strength of around 33%. This I believe is due primarily to the case as there would be little change in the strength of the core at the 20 point level of carbon due to heat treating it.

It appears, depending on the process, that color case hardening can increase steel strength
http://www.sst.net/advantages-case-hardening/

I am however looking for numbers...which are better than 1000 "expert" opinions

I should have also mentioned "cold rolling" which was used on decarbonized steel barrels as a means to increase tensile strength. The carbon steel numbers I gave are for cold rolled, not heat treated steel.

AISI 8620 is a chromium, molybdenum, nickel low alloy steel often used for frames today. It is easily carburized and machined when annealed
Carbon - .18 - .23%
Manganese - 0.7 - 0.9%
Chromium - 0.4 - 0.6%
Molybdenum - 0.15 - 0.25%
Nickel - 0.4 - 0.7%
Phosphorus - 0.035% max.
Sulfur - 0.04% max

Of interest, though slightly OT

H.P Leighly, professor emeritus of Metallurgical Engineering at University of Missouri � Rolla published a study of the steel used in the hull of the RMS Titanic in the January 1998 issue of Journal of Metals, the publication of the American Institute of Mining, Metallurgical and Petroleum Engineers
http://www.tms.org/pubs/journals/jom/9801/felkins-9801.html

Thomas Andrews, chief naval architect, and managing director of the design department at Harland and Wolff specified 1� hull steelplate with a yield strength of 40,000 psi and 30% elongation.
The �acid-lined open hearth� (not Bessemer) steel used in the construction of the hull, from the steelworks of David Colville and Co., was similar to AISI 1018 but with a slightly higher phosphorus, much higher sulfur, and lower manganese concentration. The ultimate tensile strength was 65,000 psi, yield strength 41,000 psi with 29% elongation. The low Mn:S ratio made the metal more brittle (lower impact strength) in the cold temperature.

Photomicrographs showed �dirty steel� with both silicate and sulfide (iron sulfide and manganese sulfide) inclusions; slag.

The Titanic was completed in 1912. It has been asserted by other researchers that the steel plate used was the standard for ocean liners of that period, and no steel available in 1911 could have withstood the impact with the iceberg.

So if the test sample is small and the cased component comprises the majority of the (also) heat treated material how is that supposed to apply to a shotgun action?
And I have to admit that fond as I am of CC'd guns this whole discussion ranks right up there with flame colored screws on the importance scale. Yet another topic of seemingly no importance whatsoever to the guns. Whatever it was the manufacturers did to the guns and why is not something that shooters and collectors are gonna be changing very likely.
Simple minded as I am I am faced with the burning question of "who cares" and "what difference does it make?" I suspect that would just be me.
Oh, yeah - casing can warp an action. A common concern.

The little test specimens I made were not for case hardened steels but alloy steels.
I have no idea how the tests were done for the case hardened 1020 steel I noted. Obviously it was not done in this same manner or the results would have been vastly different. If the test part was so small that the "Case" met in the middle then it would have been totally useless for case hardened parts as one would now have a High Carbon steel which was essentially through hardened.

As to who cares "Inquiring Minds Want to Know". "IF" one simply does not care I don't understand why they are still reading on page 5. I totally Skip many threads after about the first page because I have no interest in that particular thread. I am still posting here on page 5 because obviously I do Care.

Maybe, one could also add in previous case recoloring attempts after it left the maker, as possibly relevant. It would seem that casing the tang on SKB�s example to a depth of a few thousandths couldn�t impart enough depth of hardness to cause it to crack off. I�d think predictability matters, and Steve probably cared?

One thing which has always been a concern of mine. When the part was carburized in manufacture the carbon was added to some depth to the surface. This was then hardened to form the "case". Even though the colors fade the carbon is still there & unless annealed it still has its hard case. When the part is re-carburized what effect does this have on the original. what if a different medium is used, is it absolutely going to be compatible with what was used the first time etc. Does this re-carburization add to the depth of the case, perhaps making it more brittle. All things to be considered I believe.

Well I've foolishly (per Wonko) read through pages of internet "expert gun guy" verbiage about case coloring firearms. 95% is a repetition of the same stuff somebody smart must have once said, with no textbook or scholarly journal references.
The non-deep thinkin' version is that traditional charcoal color case hardening IS a form of heat treatment, and, DONE RIGHT, can increase the strength of the steel.
Still looking for numbers that are applicable to firearms but Miller's post re: case hardened 1020 is noted and appreciated

And another but relevant topic. There have been periodic posts over on Trapshooters.com by guys who wanted to fancy up their case colored Krieghoffs with custom engraving...requiring annealing...then requiring re-heat treatment...leading to fractured receivers...leading to very unhappy customers

Heat treatment tutorial
http://navybmr.com/study%20material/14250a/14250A_ch2.pdf

I do not know enough about the Krieghoffs to know what their base metal was for the frames. I know that at least some Perazzis were made of an alloy steel & heat treated & then given "Fake" colors. If an alloy steel such as this was given a traditional Case Hardening it would leave them excessively hard & brittle, could be the problem with the Krieghoffs.

king: in my opinion, your gunsmith gave you good advice...