Impact sockets are heat treated, but are not especially hard, instead they are tempered to a very tough state so they will not be brittle and crack under the pounding. They are machinable but will probably require carbide tooling. A good surface finish might be difficult. Tapping might also be difficult, choose a smaller percentage of thread depth like perhaps 55%. Those are general guidelines as I see them, but there are lots of tool makers out there, and their products are not all the same, sometimes by wide margins...