Austempering

Salt bath annealing is what you do when you want a tough bainite structure instead of brittle martensite. The part is brought to the target temperature completely in the salt bath and held there until the structure has transformed. When welding, that's the trick when you don't want to or can't cool down quickly after welding, because otherwise cracks threaten. It's important that the temperature really stays constant, otherwise the structure becomes uneven.