Case-hardening steels take their name from the surface treatment given to the parts made from this type of steel, i.e. carburizing. Carburizing is a heat treatment process in which steel absorbs carbon (from 0.80 to 2.00 mm maximum). By once more hardening and stress-relieving the steel, we can obtain a highly durable surface  and a core  which is less hard yet tough. There are different types of case hardening steels they have different chemical compositions.  . However, they allhave one thing in common: these steels have a  relatively low carbon content, which does not exceed 0.20%. When manufacturing thin working parts. only carbon steel can be used, such as C10 and C15. But on larger parts, chromium alloy steels are needed, such as 16MnCr5, 20MnCr5, which have a greater hardenability. If the dimensions are even greater and/or greater hardenability is required, it is necessary to use steels which, in addition to chromium, also contain nickel and molybdenum, such as16NiCr11 and 17CrNiMo6-4. Long rolled products in case-hardened steel are standardized in Europe by the EN ISO 683-3 standard, while cold finished products by EN 10277.