Does Heat Treatment Process Changes Composition?

Heat treatment of metals will not alter bulk chemical composition. However, it does alter microstructure wherein local compositional differences can happen.

Thank you... But...
It would be better if there are some references sir...... May be a journal or e book..

N.Gowtham RajThank you... But...
It would be better if there are some references sir...... May be a journal or e book..

<a href="https://books.google.co.in/books?id=A2QG3UssqKUC&pg=PA1&source=gbs_toc_r&cad=4#v=onepage&q&f=false" target="_blank" rel="nofollow noopener noreferrer">Heat Treatment: Principles and Techniques - T. V. Rajan, C. P. Sharma, Ashok Sharma - Google Books</a>

To state simply, heat treating of steel makes the outer surface harder as the cooling rate is high. The inner core is usually soft. The heat treatment changes the circumferential micro-structure to become Martensite.

There are different types of heat treatments for metal. Some are used to relieve streses within the metal, some are used to surface harden it. Some are used to make them tough, while some are used to reduce the hardness. This is a very broad topic, but the situation you are describing in your query is called surface hardenning. Here the metal is heated and then cooling rapidly, usually in water. Carbon molecules that migrated to the surface during heating become trapped at the surface when the object is quenched. This makes the surface very hard and the core very tough. A hammer head is engineered this way. Think about it 😉
More info? Try to get your hand on Callister's Materials Science and Engineering.

NOTE: This type of heat treating cannot be performed on low-carbon steels. For low carbon steels Carburizing is used to surface harden.

if heat treatment of a material is carried out at some specific temperature range and pressure range then by altering the micro structure the depth of the added impurity also changes according to requirement