Thermochemical processing can be used for surface property enhancement in both

carbon and alloy steels.

$($i$)$ List the four types of thermochemical process.

$($ii$)$ Define the temperature range for each thermochemical process.

$($iii$)$ Provide one example for each process including the most suitable type of

carbon and alloy steels,

$($iv$)$ Explain the main phases formed during each process that improve the surface

properties