CYANIDING NITRIDING&

-Faizan AliI2 33

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.

CYANIDING

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.

Advantages 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

Disadvantages

Cyanide salts are poisonous Cyanide attacks wounds Even fumes can cause damage Direct contact could be harmful Molten cyanide explodes on contact with

water

Precautions

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.

Cyaniding Plant

Cyaniding Material

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

Nitriding

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

Advantages 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.

Disadvantages

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

Nitriding plant

Nitrided Material

FAQs on Cyaniding

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.

FAQs on NitridingQ. What Nitrides are formed from [N]?= With plain carbon steels, Fe2n and Fe4N are

formedQ. 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