52100 steel is a high carbon low alloy steel with the minor addition of other alloying elements. The number here is according to SAE 5 digit system. In this composition, 5 indicates chromium as an alloying element other than carbon. 2 digit indicates chromium content in between 1% and 2%. The last three digits are used for carbon percentage in carbon steels. In this grade, 100 digits indicate 1095 cro-van steel contains carbon percentage equal to 1% approximately.