Cyaniding and Nitriding

Cyaniding and Nitriding

• 2.
   Providing hardwear resistant case with a tough core to the carbon steels by liquid cyanide bath.  Producing hard surface on low/medium carbon steels.
• 3.
   2NaCN +2O2 = Na2CO3 + 2N + CO2 (dissociation of carbon monoxide at steel surface)  It is carried out in a bath of 20-50% Sodium cyanide, up to 40% sodium carbonate(soda ash) with varying amount of sodium and barium chloride.  It is heated to 870-930 Celsius.  Work pieces are immersed in a molten bath of cyanide for 10-180 minutes  Then the steel is quenched in water or oil.
• 4.
   Rapid heattransfer  Low distortion(easily avoided)  Negligible oxidation or decarburisation of surface  Uniform depth  Less time consumption  Rapid absorption of carbon and nitrogen  Bright finish of machine parts
• 5.
   Cyanide saltsare poisonous  Cyanide attacks wounds  Even fumes can cause damage  Direct contact could be harmful  Molten cyanide explodes on contact with water
• 6.
   Careful handlingof cyanides is needed as these are very poisonous salts  As molten cyanide explodes with water, components must be dried carefully before dipping into molten cyanide bath.
• 7.
  Cyaniding Plant Cyaniding Material
• 8.
  Surface hardening ,devised by heating the steel in an atmosphere of ammonia.  Nitriding is the last operation after shaping and heat treatment of a machine component
• 9.
   NH3 =3H + N  It is carried out at around 500-650 degree Celsius  Hardness is from 0.2-0.4 mm  The ammonia is dissociated and [N] nascent Nitrogen combines with elements in steel to form nitrides.  These nitrides give extreme hardness to surface  Carried out for 50-90 hours  An average of 0.2 mm is produced at 500 degree for 50 hours.  Components are cooled before supplying ammonia
• 10.
   Used onautomotive, airplane and diesel engine wearing parts and many miscellaneous parts such as pumps, gears, shafts, gauges, clutches, drawing dies, clutches, mandrels, etc.  Very high surface hardening  As the nitrided parts are not quenched, there is no chance of distortion/cracking  Surface becomes resistive to corrosion, wear and fatigue  No machining of components is required after nitriding  Retains hardness up to 500 degree Celsius.
• 11.
   Its useis limited due to expense required for treatment( Very costly)  The case formed is brittle  The cycle time for nitriding is 50-90 hours  Only special types of steels can be heat treated using this process
• 12.
  Nitriding plant Nitrided Material
• 13.
  Q. How isthe hardness produced? = The hardness is produced from compounds of nitrogen and carbon present in surface. Q. What is the result of cyaniding? = An average depth of 0.125 mm produced in 15 min at 850 degree Celsius. Q. Can we obtain more thickness? = Yes, using special salts, thickness up to 0.8 mm can be obtained.
• 14.
  Q. What Nitridesare formed from [N]? = With plain carbon steels, Fe2n and Fe4N are formed Q. How do we vary steel types in Nitriding? = Low carbon content for lightly stressed parts such as spindles, gears and high carbon content steels to withstand high local pressure as in dies, blocks, and dies for plastic molding. Q. How does surface become so hard? = When ammonia contacts with steel, the dissociated [N] defuses into surface of work piece component forming hard nitrides