A steel qualifies as a carbon steel when its manganese content is limited to 1.65 percent (max), silicon to 0.60 percent (max), and copper to 0.60 percent (max). With the exception of deoxidizers and boron when specified, no other alloying elements are added intentionally, but they may be present as residuals. If any of these incidental elements are considered detrimental for special applications, maximum acceptable limits may be specified. In contrast to most alloy steels, carbon steels are most often used without a final heat treatment; however, they may be annealed, normalized, case hardened, or quenched and tempered to enhance fabrication or mechanical properties. Carbon steels may be killed, semikilled, capped, or rimmed, and, when necessary, the method of deoxidation may be specified.
Alloy Steels
Alloy steels comprise not only those grades that exceed the element content limits for carbon steel, but also any grade to which different elements than those used for carbon steel are added, within specific ranges or specific minimums, to enhance mechanical properties, fabricating characteristics, or any other attribute of the steel. By this definition, alloy steels encompass all steels other than carbon steels; however, by convention, steels containing over 3.99 percent chromium are considered “special types” of alloy steel, which include the stainless steels and many of the tool steels.
