Whenever a type of steel, with the exception of the element manganese, does not contain any element with more than 0.5% content, it is described as unalloyed. These materials have a “C” (carbon) – followed by number corresponding to 100 times the average carbon content – in their designation (for example: C 22).
Another variant of naming is that the name is composed first of a letter code describing the application, and then of a number corresponding to one tenth of the tensile strength in N/mm² (for example ST for unalloyed construction steel and 52 for a tensile strength of approximately 520 N/mm² = ST 52).
In case alloy steels do not contain any element >5%, the naming is according to the following rule. One starts with the number corresponding to 100 times the carbon content. Then follow the chemical elements which are the main characteristics of this alloy, followed by numbers which are in the order of the previously mentioned chemical elements and reflect an indication of the content. Each of the elements mentioned is multiplied by different factors (chromium by a factor of 4 and molybdenum by a factor of 10). (For example: 10 CrMo 9-10 means 0.1% C content Cr (chromium) Mo (molybdenum) 9 (9 : 4 = 2.25 chromium) 10 (10 : 10 = 1 molybdenum.)
Whenever the alloy elements are contained >5%, an additional “X” is placed in front of the “C” code.