Carbon steel, also called plain-carbon steel, is steel where the main interstitial alloying constituent is carbon. The American Iron and Steel Institute (AISI) defines carbon steel as: "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; when the specified minimum for copper does not exceed 0.40 percent; or when 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."
Carbon levels are divided as follows:
Carbon grade series are:
- low carbon = .06% to .25% carbon content (mild steel)
- medium carbon = .25% to .55% carbon content (medium steel)
- high carbon = >.55% to 1.00% carbon content (hard steel)
The second two numbers in AISI-SAE designations indicate the approximate carbon content for steel (for example, in 1018 the carbon range is .15% to .20%; .18% [shown as "18"] is the approximate carbon content).
- 10XX = non-resulpherized carbon steel, with manganese 1.00% maximum (example 1018, 1045 and 1050).
- 11XX = resulpherized carbon steel (for example 1117, 1141 and 1144).
- 12XX = rephosphorized and resulpherized carbon steel (for example 12L14 and 1215).
The term "carbon steel" may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels.
As the carbon content rises, steel has the ability to become harder and stronger through heat treating, but this also makes it less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.
Alro offers Carbon Steel in a broad spectrum of products including bar, structural, pipe/tube and sheet/plate.