Cynading and Nitriding Process- Metal Working

2.  Providing hard wear 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 heat transfer
 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 salts are poisonous
 Cyanide attacks wounds
 Even fumes can cause damage
 Direct contact could be harmful
 Molten cyanide explodes on contact with water

6.  Careful handling of 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 on automotive, 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 use is 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 is the 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 Nitrides are 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