Alloy Steel - Alloy steel is a type of steel that has presence of certain other elements apart from iron and carbon. Commonly added elements in alloy steel are manganese, silicon, boron, chromium, vanadium and nickel. The quantity of these metals in alloy steel is primarily dependent upon the use of such steel. Normally alloy steel is made to get desired physical characteristics in the steel. Alloy steels are divided into low alloy steels and high alloy steels. When the percentage of added elements goes past 8 (in terms of weight), the steel is referred to as high alloy steel. In cases where added elements remain below 8% by weight of the steel, it is a low alloy steel. Low alloy steels are more common in the industry. In general, addition of one or more of such elements to steel makes it harder and more durable. Such steel is also resistant to corrosion and tougher than normal steel. To alter the properties of steel, it needs heat treatment when elements are added to it. Carbon Steel - Carbon steel is also known as plain steel and is an alloy of steel where carbon is the main constituent and no minimum percentage of other alloying elements is mentioned. Carbon steel is not stainless steel as it is classified under alloy steels. As the name implies, carbon content is increased in the steel making it harder and stronger through application of heat treatments. However, addition of carbon makes the steel less ductile. The weldability of carbon steel is low and higher carbon content also lowers the melting point of the alloy. It is an amazing fact that of all steels used in the US, 85% is carbon steel.