Carbon Steel Fasteners

Carbon steel nut and bolt grades are divided into three different categories based on the carbon content of mild, medium and high carbon steels. Mild steel hex bolts are the most widely used category of all carbon steel groups. Mild steel threaded bolt alloys typically contain less than 0.25% carbon by weight. Since this type of carbon steel bolt cannot be hardened by heat treatment to promote the formation of martensite, the alloy is cold worked.

Carbon steel is defined as any steel with a carbon content not exceeding 2.1% by weight. Carbon steel bolts become harder and increase in strength after heat treatment as the carbon content increases. However, the ductility of the steel decreases.

Within this specific category of mild steel is another steel called High Strength Low Alloy Steel, or HSLA for short. Although HSLA screws belong to the mild steel category, it can be noted that HSLA screws also contain other elements in their alloys, such as copper, nickel, vanadium and molybdenum.