To hear treat it you need to bring the entire part up to temp and hold it for a while - temp and time will depend on the steel - then quench it prob in an oil bath that is heated and held at a specific temp. It's been a loooong while since I ran any heat treats. Add to that, you will have scale form on the part so your dimensions would be shot.
Case hardening is a different animal and only hardens maybe ten thou deep from the surface.
It is my understanding that the Brinnell Hardness of the sear and the hammer should be equal....otherwise, one part will wear faster than the other.....I have never tried to heat treat a sear....
On one gun build project I was finished doing the barrel fitting, but after measuring the lower lugs, I needed a link for the 1911 barrel, but I didn't have the right size...:scratch: I went ahead an ordered a multi pack of various links, but I decided to make one anyway. I made one very easily, and heat treated it by using the color code system, then quenched it in a pan of old motor oil..... It worked fine, and I was able to test fire the gun I had built, but I did replace the link later when my order from Brownell's arrived.