The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Steel is considered to be carbon steel when:

• no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect;
• the specified minimum for copper does not exceed 0.40 percent;
• or the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60