case color hardening

Anything to do with gun smithing.
marlin93
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Re: case color hardening

Post by marlin93 »

when the time comes for me to send parts out for charcole blueing who would you recomend? also if i need replacment screws is there a source for original ones or does marlin still make the same sizes? thanks, bill
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marlinman93
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Re: case color hardening

Post by marlinman93 »

Most of the 336 screws will fit a std. 1893 with no problems. Just order the same screws for the same locations. Brownells has them, or order from Marlin.
Marlin lever actions 1870's-WWI, Ballards, and single shot rifles!
MDH
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Re: case color hardening

Post by MDH »

Most parts in a firearm are hardened, either they are Case hardened; where it’s just the outer “skin” of the metal is hard and the core remains soft and flexible. Or thru hardened; where the entire piece (skin & core) is hardened. What determines whether a part is case or thru hardened is the application of the part and the type of metal.

Hammers, levers some frames work fine with just case hardening, and softer steels (1018/ 1020) are generally used for these applications. Springs, triggers and many screws are generally thru hardened where the hardness goes all the way thru the part; this requires different steels (1095 in the case of springs) for these applications.

Testing parts with a file is ok, but only tells you one piece. If the file slides without biting or marking the surface, the test material would be considered harder than the file. If the file bites or marks the surface, the test material would be considered softer than the file. A typical file is around HRC 60-61 (Rockwell scale). So if a file bites into the material then yes the material is softer than the file but how much softer? It may have been heat treated to HRC 40-45, which a file will easily mark, but is still considered heat treated (Hardened).

Most case hardened parts are quenched in water; most thru hardened parts are quenched in oil.

As to bluing, as Jim stated, most blued frames were charcoal blued, smaller parts (screws, springs pins etc) were Nitre blued.

I disagree with Jim on barrels & magazine tubes; I believe they were rust blued. You can get a very nice finish with rust bluing; it all depends on how long you let the parts rust before boiling and carding. The longer you allow it to rust the more matted the appearance.

There’s a neat movie “History of Marlin Firearms” that clearly shows Marlin rust bluing the barrels.
mdeland
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Re: case color hardening

Post by mdeland »

I've have hot bluing tanks and have been doing that for about 30 years but now mostly cold rust blue using the Niedner method and solution. It surely does bite the metal and leave it flat, which I really like for most applications. My color is not black like the hot blue but rather dark brown and is very durable.
I have not tried the hot nider bluing but am very interested as I sure like the colors you got Jim. I think Roy Dunlaps book has the chemicals and method instructions so will not bother you about that. How durable is it? Mike D.
Jim D
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Re: case color hardening

Post by Jim D »

Mike,

The chemical for nitre bluing is nothing more than Potassium Nitrate. It melts at around 750F. I take it up to 850F for bluing. If you try this, be VERY, VERY carefull. If there is ANY moisture on the part it will splatter and shoot molten KNO3 all over the place. If even one drop hits you, you will have a severe burn. The bluing wears fairly well. Not as good as modern bluing salts, but not bad.

Brownells sells nitre bluing salts which are designed to melt at a lower temperature. If you are wanting to duplicate the "fire blue" color like you see on screws etc, this is what you want to use. The fire blue color appears at around 690F I believe. When you go above this temp you eventually get the blue/black color.

The charcoal bluing wears very well.

Jim
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