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Cyaniding in Heat Treatment of Metals:

 It is  a process of producing hard surface on low carbon or medium carbon steels by immersing the steel in a molten salt bath containing cyanide maintained at 800*C to 900*C and then quenching the steel in water or oil. The hardness produced by this treatment is due to the presence of compounds of nitrogen as well as of carbon in the surface layer. 

A bath containing one-third each of sodium - chloride, sodium carbonate and sodium cyanide is used for the cyaniding treatment. Under average conditions, a depth of case of  0.125 mm will be produced in about 15 minutes at 850*C. But special salt compositions are available which enable much thicker cases to be obtained, if required. Cyaniding is used chiefly for cases not exceeding about 0.8 mm in thickness.

One advantage of  this process is that the bright finish of  machined parts can, if required, be maintained ; a second is that distortion is more easily avoided ; a third is that the change in hardness from the case to the core is more gradual and flaking  of the case is eliminated. 


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