High Carbon Steel : 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, higher carbon content reduces weld ability.
Chrome Vanadium: Chrome vanadium is a type of spring steel that was pioneered by Henry Ford for use in the Model T in 1908. It contains approximately 0.8% chromium and 0.1-0.2% vanadium, which improves the strength and toughness of the material when it is heat treated.
Chrome molybdenum: Chrome molybdenum, also known as chrome alloy or chromoly, is a steel alloy that contains chromium and molybdenum among its alloying elements. It is more costly to produce than chrome vanadium and, as a result, is usually only found in higher grade and more expensive tools. Chrome molybdenum is more ductile than other forms of steel used for socket production. Because of this, it’s often used to make impact sockets, as the increased ductility makes it less likely to shatter from the high torque and vibration of an impact wrench.
S2 Steel: S2 steel is harder than chrome vanadium or 8650 steel, but it is also less ductile and, as such, more prone to shattering. It is more expensive to produce than 8650 steel or chrome vanadium and this, along with its lower ductility, means it is only used by a few manufacturers. It is most frequently used for making screwdriver bits and screwdriver bits for two piece socket bits.
Chrome Vanadium Molybdenum (CVM): CVM is meant to give similar properties to chrome vanadium but with reduced brittleness due to the addition of molybdenum. It is used mainly in the production of screwdriver bits that are intended for use with impact tools, as the molybdenum content makes it far less likely to shatter than S2 steel.
Protanium: Protanium is a type of steel developed specifically for use in hex tools and sockets. It is claimed to be the hardest and most ductile steel used for such tools. Protanium has a high wear resistance when compared to other steels.