Mild steel (iron with a low carbon content that is strong and ductile, but not easily tempered), also known as plain carbon steel and low carbon steel, is the most common type of steel used today because it is relatively inexpensive while offering material properties that are acceptable for many applications.
Mild steel contains approximately 0.05-0.25% carbon, making it ductile and malleable. Mild steel has relatively low tensile strength, but is inexpensive and easy to form; surface hardness can be increased by carburizing.
In applications where large cross sections are used to minimize deflection, yield failure is not a risk, so mild steel is the best choice, such as structural steel. Mild steel has a density of approximately 7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3) and a Young's modulus of 200 GPa (29,000 ksi).
Mild steel suffers from yield point runout because the material has two yield points. The first yield point (or upper yield point) is higher than the second yield point, and the yield drops off sharply after the upper yield point. If mild steel is only subjected to stress at a point between the upper and lower yield points, a Lüder band will form on the surface. Mild steel contains less carbon than other steels and is easier to cold form and therefore easier to handle.
