While on this subject of "Color Case Hardening" I have a question. In all my years as a machinist whenever a part was Case Hardened (Carburized & heat treated, though often in one process) it was always "Drawn" after quenching, usually at around 300°-350°F. I once saw a young man who was going to trade school & had built a set of what we referred to as 1-2-3 blocks. He had case hardened them & ground to finish within +/- .0002" tolerance & was very proud of them. He however did not draw them & the next day they were simply SCRAP. The entire surface of the case was checked & cracked. The Drawing process was for the elimination of this surface cracking of the brittle surface.
To date I have never seen this drawing mentioned in relation to the Color Case Hardening of firearms parts. Was this simply not done & if not what kept them from developing these surface checks, which would be totally unacceptable.
In order for a piece of iron or steel to harden it must have sufficient carbon content, generally at least 30-35 points (.3-.3˝%). In case hardening exposing the surface of the part to a carbon rich substance while under heat causes the surface to absorb the carbon. Deeper depths of case require longer periods of heat. For hardening to take place requires the part be quenched from a above its "Critical Temperature". At this temp the molecules are rearranged & the part loses its ability to magnetic properties.
Any time a piece of steel is heated to this point & quenched there is a possibility of some warpage &/or size change. For this reason personally I have never decided to have one of my guns re-cased hardened.
Colors can be obtained by re-absorbing carbon into the surface & quenching from below this critical temp. To do so however would Draw the temper of the original process to a very low surface hardness, not an actual anneal, but close to it. Personally I would much prefer to retain my original case hardness than to restore the colors at the cost of the surface hardness & would never have a gun of mine so colored.
It is of course true that even the mild steel the frames are made of are sufficiently strong to contain the forces of firing, in fact they were normally proof fired "In the White" but the hard case was put there for a purpose & I prefer to retain it.
It is noted when these guns were built they were both Soft & Hard Fit. The soft fitting was the mating of the parts prior to heat treatment. After the hardening there would be some warpage. The "Hard Fitting" consisted of literally Hammering them back to a fit.
"IF" any desire to have a frame re-color cased be certain you trust it to someone who knows fully what they are doing & understands the possibilities. Also from my standpoint I would say make certain they are actually going to re-harden it & not just re-color it. If anyone tells you there is no chance of warpage in their process "AVOID THEM LIKE THE PLAGUE" they either don't know whereof they speak or they are outright LIARS.
