Details
Material hierarchy: Metal - Ferrous metal - Steel
Plain carbon steels contain carbon as the principla alloying element, with only small amounts of other elements (about 0.5% manganese is normal). The strength of plain carbon steels increases with carbon content.
According to a designation scheme developed by the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE), plain carbon steels are specified by a four-digit number system: 10XX, where 10 indicates that the steel is plain carbon, and XX indicates the percent of carbon in hundredths of percentage points. For example, 1020 steel containes 0.20% C. The plain carbon steels are typically classified into three groups according to their carbon content:
• Low carbon steels contain less than 0.20% C and are by far the most widely used steels. Typical applications are automobile sheetmetal parts, plate steel for fabrication, and railroad rails. These steels are relatively easy to form, which accounts for their popularity where high strength is not required. Steel castings usually fall into this carbon range, also.
• Medium carbon steels range in carbon between 0.20% and 0.50% and are specified for applications requiring higher strength than the low-C steels. Applications include machinery components and engine parts such as crankshafts and connecting rods.
• High carbon steels contain carbon in amounts greater than 0.50%. They are specified for still higher strength applications where stiffness and hardness are needed. Springs, cutting tools and blades, and wear-resistant parts are examples.
Increasing carbon content strengthens and hardens the steel, but its ductility is reduced. Also, high carbon steels can be heat treated to form martensite, making the steel very hard and strong.