Liquid carburizing is a process that is usually used for small and medium-sized parts. In the salt bath the carbon to be diffused in the workpiece comes from a molten salt that is a mixture of sodium cyanide (NaCN) and barium chloride (BaCl2).
Carburizing in salt bath comes with the advantages of a flexible use, great temperature uniformity around the part and it is quite easy to control.
The parts that are going to be carburized are placed in molten salts an are treated at temperatures – quite similar to the treatment in furnaces – at around 850 to 950 °C. The targeted carburization depth is rather low and below 0,5 mm. Therefore, process times are usually short. By constantly monitoring the concentrations of potassium cyanide and potassium cyanate the process remains stable and reproducibility is guaranteed.
After the carburizing the workpieces are usually quenched in another salt bath at lower temperatures between 160 and 200 °C. Again, the advantage of using molten salt is a very high uniformity of the quench effect on the workpiece without any kind of vapor bubbles. To finish the process, the parts are then treated in a tempering furnace to relieve stresses in the material structure and to reduce sensitivity to grinding cracks.
fields of application
Salt bath carburizing is used for smaller parts and parts that would otherwise be distorted easily in a furnace.
However, due to the use of the salt that contains cyanide there are doubts using this treatment from an environmental standpoint. A heat treatment provider must be aware about proper disposal of waste.