The difference between salt bath and other heat treatment methods is that when the workpiece is heated, it is immersed in melted inorganic salt. Modern salt bath equipment can control the heating temperature to within 1 degree Celsius difference. Molten salt conducts heat much faster than other traditional methods, so the heating process of the workpiece is a lot faster, easier to control and more uniform. Because of the existence of molten salt, the workpiece is insulated from the environment during heating, thus avoiding the occurrence of oxidation, decarbonization and other unwanted phenomena. In the process of removing and transferring the workpiece from the molten salt pot to the cooling medium, the molten salt forms a protective layer on the surface of the workpiece preventing the occurrence of oxidation and decarbonization. Because the temperature of molten salt can be precisely controlled, the workpiece can be transferred in molten salt pots with different temperatures to achieve mar-quenching.