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Elements Commonly Specified in Steels

Elements Commonly Specified in Steels

Carbon is the principal hardening element in steel, and as carbon content increases the hardness increases. Tensile strength also increases with the carbon content up to about .85 per cent carbon. Ductility and weldability decrease with increasing carbon.

Manganese contributes to strength and hardness, but to a lesser degree than carbon. The amount of increase in these properties is dependent upon the carbon content. i.e., higher carbon steels are affected more by manganese than lower carbon. Manganese tends to increase the rate of carbon penetration during carburizing.

Phosphorus in appreciable amounts increases strength and hardness, but at the sacrifice of ductility and impact toughness, particularly in higher carbon steels that are quenched and tempered. Consequently. for most applications phosphorus is maintained below a specified maximum.

Sulfur. Increased sulfur content lowers transverse ductIlity and notched impact toughness, but has only a slight effect on longitudinal mechanical properties. Weldability decreases with increasing sulfur. Sulfur is added, however; to improve machinability

Silicon is one of the principle deoxidizers used in steelmaking, and, therefore, the amount of silicon present is related to the type of steel. Silicon increases strength and hardness.

Nickel provides such properties as improved toughness at low temperatures, good resistance to corrosion when used in conjunction with chromium in stainless grades, deep hardening, and ready response to conventional methods of heat treating.

Chromium exerts a toughening effect and increases hardenability, it also improves the surface resistance to abrasionand wear and is used extensively to increase the corrosion resistance of steel.

Molybdenum promotes hardenability in steel, and is useful where close hardenability-control is essential. It increases depth-hardness and widens the range of effective heat-treating temperatures.

Vanadium is used to refine the grain size and enhance the mechanical properties of steel.

Aluminum is a reliable deoxidizer because of its great affinity for oxygen. It produces fine austenitic grain size.

Boron is a non-metallic element added to some steels primarily to improve hardenability and to increase the depth at which the steel will harden when quenched.

NOTE: Elements and mill terms are selected and adapted from a number of sources. More complete information may be found in publications of ASM, ASTM, SAE, AISI or other authoritative sources.