Quote:
Originally Posted by steelslaver
While those temps MAY cause those colors to appear it is far from hard and fast. The color that can appear in a piece of polished steel when heating depends on the alloy, the atmosphere and any possible contaminates in it (oil, carbon etc) as much as the temperature. Plus the color is extremely thin. I have colors show up all the time tempering knife blades. If I take 1095 and don't do anything about the atmosphere it will USUALLY turn straw at 400f if I put it in a air tight foil packet with a bit of paper the paper will smolder, use up the oxygen and it will probably be blueish. Coloring steel is an art more than a science....
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Much more true now, but in the 1800s through the early 20th century, temper colors were an easy and pretty repeatable method of controlling final heat treat in a production environment. Especially under the watchful eyes of experienced workers and inspectors for military items such as the Swiss revolver above.
As for TiN coating of action parts, it's just another take on case hardening, hard chrome, etc. QPQ nitriding noted above may be an option if the final polish doesn't round off edges of the tiny sear surfaces.