Case-hardening steels are low carbon, unalloyed or alloyed steels used in the manufacture of parts resistant to variable and impact stresses, where hard and wear-resistant on the surface and softer and tough properties are desired in the core.  The carbon content of hardening materials is between 0.10-0.20%, in some varieties it can go up to 0.25%. They can be produced with or without alloys.  The case hardening process improves surface hardness, wear resistance and continuous strength, as well as core strength and ductility. This enables the transportation of large loads and to meet impact loads.  These features are imparted to the part by impregnating the steel surface with carbon. Hardening steels are used in the manufacture of parts such as gears, shafts, piston pins, chain links, chain sprockets and rollers, discs, guide bearings, rolling bearings, rollers, some measuring and control instruments, parts with medium or high stress, parts shaped by cold blowing or spraying (extrusion), cutting tools.  The use of case hardening steels offers the following advantages over the use of high carbon steels which will give the same hardness value on the surface:
Since the hardening process is applied after the part has been partially or completely finalized, it is very easy to machine the part.
If there are parts on the surface of the part that will be machined later and do not require hardening, these areas are covered by coating with special paste or electrolytic copper. The hardening process cannot affect these parts, so they are easily machined afterwards.
After hardening, the core area will remain soft, so the distortions that may occur during hardening are very small.
The inside of case-hardened steels can be easily machined.
The case hardening steels are cheaper than high carbon steels, often tool steels, which can give the same hardness on the surface.