AISI 6150 steel is chromium vanadium type spring steel. It’s a similar alloy steel to 5150 steel with small, but effective, vanadium addition, to import greater hardness.
Steel C45 Round Bar is an unalloyed medium carbon steel, which is also a general carbon engineering steel. C45 is a medium strength steel with good machinability and excellent tensile properties. C45 round bar steel is equivalent to BS 970 EN8 or 080M40.