Alloying can be defined as mixture of metals. Steel is a mixture of iron and other elements but mostly Carbon and the carbon in a steel alloy most likely contribute up to 2.1% of its weight.
The process of alloying is used to alter the chemical composition of steel and develop its properties over carbon steel or adjust them to meet the prerequisite of specific applications.
Alloying elements are incorporated in steel for the following reasons:
- To advance mechanical properties through control of the factors which manipulate hardenability, and to allow higher tempering temperature while upholding high strength and get better ductility,
- To enhance mechanical properties at high or low temperatures,
- To augment resistance to chemical attack and to high temperature oxidation and
- To influence additional particular properties such as magnetic permeability & Neutron absorption
There are some common steel alloying agents or elements which show particular effects on the properties of a stainless steel.
Some of them include:
Aluminum (Al): If used in consideration, aluminum helps in improving the oxidation resistance. It is used to limit the growth of austenite grains.
Chromium (Cr): It is an important agent in the stainless steel. It helps in improving corrosion resistance, wear resistance, response to heat treatment, strength.
Copper (Cu): Also like Chromium, this agent also increases corrosion resistance and can be added to improve formability and to lessen work hardening in grades designed for improved machinability
Cobalt (Co): Cobalt is used in martensitic steels where it helps in increasing hardness and tempering resistance. It enhances strength at high temperatures and magnetic permeability.
Tungsten (Tu): It is present as an impurity in the majority of stainless steels and produces stable carbides, refines grain size.
Vanadium (Va): Like titanium and niobium, this agent produces stable carbides which increases strength at high temperatures. By promoting a fine grain structure, ductility can be retained.
Nitrogen (N): It increases the austenitic stability of stainless steels and enhances the yield strength in steels.
Lead (Pb): Though virtually insoluble in liquid or solid steel, it is sometimes added to carbon steels by the use of mechanical dispersion during pouring in order to make better machinability.
Phosphorus (P): Phosphorus is often added along with sulfur in order to improve machinability in low alloy steels. It even adds strength and increases corrosion resistance.
Sulfur (S): Sulfur is added to particular stainless steels to increase their machinability. At the levels present in these grades, sulfur somewhat lessens corrosion resistance, ductility, weldability and formability.
Silicon (Si): Silicon elevates resistance to oxidation both at high temperatures and in powerfully oxidizing solutions at lower temperatures. It advances ferritic microstructure and increases strength.
