Austempering
Heat treatment to produce a bainitic structure by quenching into a salt or metal bath above the martensensite start temperature and holding isothermally. This minimizes distortion and maximizes toughness at high hardness.
When austempering, you don't let the workpiece cool down completely to martensite after hardening, but hold it in a salt bath at an intermediate temperature. This creates a bainite structure that is tougher and less prone to cracking than conventionally hardened steel. If you have to weld afterwards, be careful: the heat input can destroy the fine structure again and you lose the good properties. Keep the component as cool as possible during welding and control the cooling, otherwise you'll end up with a hard, brittle part that will crack under load.