Question

Nitriding is a process of heating steel in atmosphere of :
(a) \[N{{H}_{3}}\]
(b) \[{{N}_{2}}\]
(c) \[{{O}_{2}}\]
(d) \[C{{O}_{2}}\]

Answer 1

Hint: Nitriding is the process which is done in the presence of heat during which nitrogen gets diffused into the surface of the metal so that a case hardened surface is formed. This process is used widely in high carbon, low alloy steel. During this process the volume of the component gets increased.

Complete answer:
It is a surface hardening process. There are different types of nitriding processes such as gas, plasma and salt bath nitriding. Gas nitriding is the thermochemical case hardening process which is done to increase the resistance. It is done by dissolution of nitrogen and hard nitride precipitation. Plasma nitriding is the new or modern thermochemical process which is carried out with the mixture of hydrogen, nitrogen. In this mixture carbon spending gas is optional. The nitrogen rich nitrides are formed on the surface during this process. Salt bath nitriding is the process in which the parts are submerged under molten salt. The molten salt is usually of cyanide. Nitriding is the process which improves the corrosion resistance. It is the surface modification process. It increases the hardness of steel as it diffuses the nitrogen atom in the surface of steel. The storage of nitrogen atoms and the chemical reaction increases the hardness of the surface.

As long the nitriding treatment is the harder is the surface. Nitriding is the process of heating steel in the atmosphere of ammonia. Hence the correct option for this question is option ‘a’. the ammonia is used in nitriding because it contains a donor nitrogen atom. When ammonia comes in contact with heated surfaces it dissociates into nitrogen and hydrogen. Then they get diffuse into the surface of the material.

Note: The atmospheric nitrogen is not used in the nitriding process. The reason is that it forms the molecule. Being a molecule it cannot be absorbed by steel which is essential in the nitriding process. Nitriding is usually done with aluminium, titanium, and ferrous molecules.