Any alloy of iron mixed with a small amount of carbon to increase its strength or malleability is called Steel. 
<h3>Why we use alloy ?</h3>
The most common reason for alloying is to increase the strength of a metal. This requires that barriers to slip be distributed uniformly throughout the crystalline grains. On the finest scale, this is done by dissolving alloying agents in the metal matrix (a procedure known as solid solution hardening).
It increases tensile strength also. Hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It increases the rate of carbon-penetration in carburizing. 
<h3>How to make Alloy? </h3>
Alloys are made by mixing two or more elements, at least one of which is a metal. This is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. 
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