Oct 11, 2019 · Carbon Manganese Steel Definition. Carbon Manganese Steel Definition. Keith Morris (Mechanical) (OP) 11 Oct 19 16:08. Hi all. I'm writing a subsea fatigue standard based on DNVGLRPC203. The standard states that it is valid for carbon manganese steels (CMn) but nowhere in any DNV standard does it define a carbon manganese steel. Does .