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 )

SILICON ( Si )
One of the principal deoxidizer used in steel-making and therefore, the amount of silicon present is related to the type of steel. Silicon enhances resistance to scaling and is therefore used as an alloying agent in high temperature steels. Since, however, it impairs hot and cold workability, machinability, its alloying percentages should be strictly controlled. It has only a slight tendency to segregate. In the lower carbon steels, increased silicon content is detrimental to surface quality. Where silicon killed steel is required, additional billet conditioning is necessary to ensure a good quality surface, particularly with resulfurized steel.

SULFUR ( S )
Of all companion elements in steel, sulfur shows the strongest tendency to segregate. Iron sulfide produce red or hot-shortness because the low melting eutectic forms a network around the grains so that these hold but loosely together, and grain boundaries may easily break up during hot forming; these phenomena are even enhanced by oxygen. Since sulfur has a particularly good affinity to manganese, it can be fixed in the form of manganese sulfide which are the least dangerous of all inclusions, being finely dispersed in steel and having a high melting point. Sulfur is used as an alloying addition in free-cutting steels; the finely dispersed sulfide inclusion interrupt the continuity of metal structure, thus producing short chips in machining. Sulfur decreases weldability, impact toughness and ductility.

TIN ( Sn )
Can render steel susceptible to temper embrittlement and hot shortness.

VANADIUM ( V )
Refines the primary grain; hence also the as-cast structure. Additions of vanadium up to 0.05% increase the harden ability of medium-carbon steels; larger additions appear to reduce the harden ability due to the formation of carbides that have difficulty dissolving in austenite. It is a strong carbide former, increases wear resistance, retention of cutting edges and high temperature strength. Therefore, preferred as an additional alloy material in high speed steels, hot work and high temperature steels. Vanadium greatly improves red hardness and diminishes overheating sensibility.

WOLFRAM ( W = TUNGSTEN Tu )
Powerful carbide-former; its carbides are very hard. It improves toughness and inhibits grain growth. It increases hot strength and hardness retention as well as wear resistance at high temperatures ( red heat ) and cutting power. It is a favorite alloying element in high speed and hot work steels, high temperature steels and super hard steels.

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