Bright hardening treatments can be performed on parts of made of alloy composition capable of hardening without water, oil, or salt quenching.  Tool steel parts made of air hardening alloys are typically bright hardened in batch vacuum furnaces.  Small investment castings, stampings, springs, and screw machine parts are typically bright hardened in batch vacuum furnaces or in continuous hydrogen atmosphere belt furnaces.  The advantage of bright hardening is the production of a heat treated part of very high surface quality with minimal additional finishing required.