Case hardening is little different than surface hardening, even though both have similarities in cooling processes.

In case hardening the metal block is heated in the furnace and the quickly is introduced in cooling bath.

Due to that the elements infuse on the surface making a hard casing layer over material.

Inner core remains soft but the casing is formed making it hard protecting core.

The casing is tough protection to external wear and tear and abrasion.

It is used for low carbon steel for hardening process.

It is heated until it becomes red hot, then it is quickly introduced to element that is going to infuse.

Then the steel is again heated to red hot and then is cooled by quenching it in water bath.

To increase the case depth, the process is repeated several times.

One of the most common element to infuse is carbon and charcoal is used for it.