ALLOYING ELEMENTS IN STEEL

Alloying elements are classified according to their faculty in forming carbides, austenite or ferrite, and with a view to the purpose for which they are added to ordinary steels. According to the alloying percentage, every element can impart unique and specific characteristics to the steel. The combination of various elements, as utilized in modern metallurgy, can enhance this effect. However, certain combinations of alloying elements may result in constituents which, far from producing a favorable cumulative effect with regard to a certain property, may counteract each other. The mere presence of alloying elements in steel is but a basic condition for the desired characteristic which can be obtained only by proper processing and heat treatment. The principal effect and influences of alloying and accompanying elements are outlined below.

CARBON ( C)
ALUMINUM ( AL )
ANTIMONY ( Sb )
ARSENIC ( As )
BERYLLIUM ( Be )
BORON ( B )
CALCIUM ( Ca )
CHROMIUM ( Cr )
COBALT ( Co )
COPPER ( Cu )
HYDROGEN ( H )
LEAD ( Pb )
MANGANESE ( Mn )
MOLYBDENUM ( Mo )
NICKEL ( Ni )
NITROGEN ( N )
OXYGEN ( O )
PHOSPHORUS ( P )
SILICON ( Si )
SULFUR ( S )
TIN ( Sn )
VANADIUM ( V )
WOLFRAM ( W = TUNGSTEN Tu )

MANGANESE ( Mn )
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. Manganese is a deoxidizer and degasifier reacting favorably with sulfur to improve forging ability and surface quality as it converts sulfur to manganese sulfide, thereby, reducing the risk of hot shortness, or susceptibility to cracking and tearing, at rolling temperatures. Manganese increases tensile strength, hardness, harden ability, resistance to wear, and increases the rate of carbon penetration in carburizing. It has a moderate tendency to segregate. The presence of manganese increases the coefficient of thermal expansion but reduces both thermal and electrical conductivity.

MOLYBDENUM ( Mo )
Is chiefly used in conjunction with other alloying elements. Its presence reduces the critical cooling rate and improves harden ability, hardness, and toughness, as well as creep resistance and strength at elevated temperatures. It helps to prevent temper brittleness and promotes fine grained structure. It increases both yield point and tensile strength. It forms carbides readily and thus improves the cutting properties in high speed steels. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements.

NICKEL ( Ni )
Increases considerably the impact strength of engineering steels, even in low temperature ranges, and is therefore used as an alloying element in steels for case-hardening and for hardening and tempering as well as in low-temperature steels. Nickel lessens distortion in quenching and broadens the temperature range for successful heat treatment. It increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high-chromium ( stainless ) steels.

NITROGEN ( N )
Is present in all steels, but usually in small amounts; it will combine with certain other elements to precipitate as a nitride. This increases hardness, tensile and yield strength, but it decreases toughness and ductility.

OXYGEN ( O )
Injurious to steel, its specific influence depends on the type and composition of its compounds in steel and on their shape and distribution. It weakens mechanical properties, in particular impact strength, especially in the transverse direction, whereas the tendency to aging brittleness, red shortness, woody and slanty fracture is increased.

PHOSPHORUS ( P )
In appreciable amounts, phosphorus increases the strength and hardness of hot rolled steel to about the same degree as carbon, but at the sacrifice of ductility and toughness, particularly in the quenched and tempered condition. Consequently, for most applications, phosphorus is generally maintained below a specific maximum. This varies with the grade and quality level. In certain low carbon free machining steels, higher phosphorus content is specified for its beneficial effect on machinability. Phosphorus has a pronounced tendency to segregate.