doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Annealing before re-casing, is this BS ?

Just got off the phone with John G. We spoke of both the metallurgical and practical aspects of case hardening and coloring. The gist is as follows.

Metallurgically, annealing before re-case hardening is not necessary. All hardness is lost when the metal temperature goes above critical; the metal has no "memory" of hardness. Practically, most parts will require some amount of polishing/pit removal/re-engraving which will be vastly easier to do after annealing. Further, a part retaining the original "skin" hardness is more likely to be filed/ground/polished in a way that leaves the "skin" thickness uneven - remember that case thickness is on the order of 0.002" - 0.003". Re-casing will increase the "skin" thickness and surface carbon content. But, it will not completely even out the thickness. Thinner parts are more likely to warp from an uneven "skin" thickness.

Warped parts can generally be bent back to working dimensions due to the core softness of the metal and the thinness of the hard "skin".

Repeated case hardening cycles will produce poorer colors due to increasing carbon content at the surface (high carbon steel is more resistant to oxidation than is low carbon) and thicker "skins" that are more prone to warping and to cracking. Smaller/thinner parts are more subject to this than are bigger/thicker parts.

Modern alloys can generally be case hardened without through hardening due to the higher critical temperature of such alloys. Also, those parts that are through hardened can be case hardened and colored without loss of all through hardness as case hardening/coloring temperature is around 1250 degrees F.

Oxide colors can be restablished at temperatures in the 700 degree F range. John tells me that some of the CC colors do not appear in oxide coloring and will be absent unless the part is heated to the afore mentioned 1250 degree range and submersed in casing material. He should know better than I do.

In sum, most parts will need to be annealed prior to re-casing. Warping is a fact of life and not the end of life. There is a very finite number of times a part can be re-cased; for very thin pieces that may be only one (the original). Oxide colors can be re-established without rehardening, but true CC can only be re-established via re-casing.

Hope that helps some.

I have a good friend that has reestablished colors on perhaps 20 double guns at his home workshop using bone charcoal pack, quenching in highly oxygenated water after heating to around 650 degrees in his heat treating oven. His colors are very nice and do not look cheap or tacky. They may lack some of the colors that are possible to achieve at the 1200+ degree range. My question is, can variation of the pack materials help achieve some of those colors at low temps that are normally brought out at the higher temps, or is it only possible to get those colors by going to the higher temps? If so, why risk the higher temps if polishing or chasing of engraving is absolutely not necessary?

Stan

Stan et al:
Perhaps this will be of interest.
I have mentioned this before but will mention again.
About three years ago I have the great pleasure to examine a beautiful gun that was custom built in the Tula (USSR) Arsenal. It had bee a presentation piece from Kruschev to Wilson.
This gun had the most incredible colors. It was pink, reddish, orange, green, blue and light purple. The overall tints were subtle and astounding beautiful. Much like the most lovely sky just before the sun sets.
I posted the question of how these colors were gained and our friend, Geno answered. He stated that is one used powdered leather charcoal as well as bone, this was the result.
I think that the reason that I was so smitten with these subtle colors is that they did not camouflage the the beautiful engraving as does deep colors.
perhaps we can encourage some to try this. I think I may with the Pedersen at some time.
Best,
John

Thanks Rocketman.

Yes, this one has been just a bit more revealing than our 1001 previous disputations over Martensite and the critical temp. For me, it's a keeper. And thanks to John Gillette also.

jack