Cooter
I've made a couple hundred gigs over the last 30 years or so for the giggers around here. I forge most of mine from old pitchforks and then weld on a half inch round mild steel shaft and a handle socket made from 16 guage sheet. I have made some from car spring, slit the tines with a hot cut and then forged to shape, all one piece including the forged handle socket.
Either way, I just let the gig normalize after forging and then heat treat only the points. I heat the points up to the barbs to critical and then quench in oil. I polish the points a bit to see the temper colors and then using a propane torch start heating the hardened tip back behind the barb and watch the colors run to the tip. I temper mine to a dark purple or so.
I have had good luck with this process, but no matter how hard the tips they will still wear when gigging in gravel bottom streams. Also, if you leave them too hard they WILL break. I still have one of the first gigs I made and still use that I have rebarbed a couple times now as the points have worn down.
I like to keep a very sharp point on the gigs that I use, which means I touch them up after every use. The points are too hard to file, so this means using an angle grinder or a sanding belt to sharpen them.