The Collaborative International Dictionary
Carbon steel \Carbon steel\ Steel deriving its qualities from carbon chiefly, without the presence of other alloying elements; -- opposed to alloy steel.
Wiktionary
n. Any of a range of alloys of iron and carbon whose properties depend on the proportion of carbon.
WordNet
n. steel whose characteristics are determined by the amount of carbon it contains
Wikipedia
Carbon steel is steel in which the main interstitial alloying constituent is carbon in the range of 0.12–2.0%. The American Iron and Steel Institute (AISI) definition says:
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.
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 percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.
Usage examples of "carbon steel".
The more carbon steel has, the more pearlite is formed, and the harder the steel is.
The best sword steel is made of thousands of thin layers of hard high-carbon steel welded between layers of flexible low-carbon steel.
The high-carbon steel corrodes less quickly, and the result is a surface that looks like ripples on water, hence the name.
The pikes were made of low-carbon steel and would rust quickly in the salt environment but they were all that were available.
Last, but not least, since they were not penetrators, they were made out of simple carbon steel.
But because they'd never developed electricity, there was no stainless steel, and no electroplating, so the rifle was made out of a strong, medium-carbon steel that was anything but rust-proof.