Cyaniding

Cyaniding:

In this process the parts to be treated are immersed in a liquid bath at 800-960— C of Sodium Cyanide (NaCN) with the concentration of 25-90%. A measured amount of air is then passed through the molten bath. NaCN reacts with oxygen and get oxidized.

1. 
   2NaCN + O2          2NaCNO
2. 
   2NaCNO + O2       Na2CO3 + CO + 2N
3. 
   2CO                       CO2 + C

Carbon and nitrogen formed in atomic form diffuses in steel to form a thin wear resistant layer of carbonitride. Usually this process requires 30-90 minutes for completion. For obtaining case depth from 0.5 to 2mm, process is carried out at higher temperature 950— C in a bath containing 8% of NaCN, 82% of BaCl2 and 10% of NaCl. This process takes 1.5-6hrs for completion. For a case depth of 0.13 to 0.35mm the bath is maintained at a temperature of 850— C. the higher the temperature at a given cyanide level the higher is the percentage of carbon diffusion. After cyaniding the pieces are taken out and quenched in water or oil. The parts are then subjected to low temperature tempering. This process is not suitable for parts, which are subjected to shock, fatigue and impact because the addition of nitrogen has adverse effects on such properties of steel.