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Old 09-08-2009, 06:01 PM
davidj davidj is offline
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This is becoming an old thread but I got some additional information and wanted to pass it on.

First, I reviewed a couple industrial/manufacturing books from the first half of the Twentieth Century and determined that carbonia oil was NOT unique to Smith & Wesson. Or even to guns. There were many applications in which manufacturers used carbonia oil in a heat treat/temper furnace to color metal. However, it appears that the specific bluing process used by Smith & Wesson WAS secret and proprietary.

Second, to respond to comments, it is unlikely that the parts were "quenched" in oil...or in anything else. The temperature at which S&W was "cooking" guns was not enough to impart a significant heat-treat effect. Generally stated carbon steel needs to go to the 1400 F or so range and then be quenched (cooled as rapidly as possible) so that the carbon crystalline structure will solidify. Heating to 750 F and quenching wouldn't accomplish that much.

But heating to 750 F and cooling slowly would make a lot of sense. When high carbon steel is heat-treated, it becomes brittle. The hotter the steel is heated and the faster it is cooled, the more significant brittleness is. Generally stated you do not want brittle steel in a gun. While brittle (hardened) steel has much higher tensile and yield strengths than mold steel, it is much more susceptible to dynamic forces. When it fails it is much more likely to fail catastrophically (e.g. shatter/"blow up"). So because of this, the normal practice is to heat treat and to then heat the steel item to a midway temperature (say, 750 F, perhaps) and then let it cool slowly. This relieves some of the internal stresses that developed in the steel during the initial heat-treat and quench, and it gives the resulting steel item more elasticity and resilience (but lower tensile/yield strength than an untempered, hardened piece of the same steel). Normally you consult the data sheets for the steel you are using to figure out how how it should be heated for both hardness treating and tempering.

So the point is -- it would seem that S&W was likely doing 2 things at once here. First, they were tempering the steel. Second, they were giving it a charcoal blue finish, albeit in a "dry" environment.

This begs the question (at least for me), do you need to go to 750 F to replicate this dry charcoal process? Or could you get good results at 500 or 550 F?

BTW - I also reviewed "Smith & Wesson Revolvers: The Pioneer Single Action Models" by John E. Parsons. Nothing about bluing methods. It did mention that S&W shipped out guns for plating (at least in the early days) and it also mentioned that there was a small run of color case hardened No. 1-1/2's (which seemed interesting on a couple levels...).
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