Carbon steels in their commercial forms all times comprise specific amounts of other elements. A lot of of these elements enter the steel from the ores and it is complex to remove them during the procedure of steel making. Each commercial steels comprise varying amounts of Mn, Si, S and P and frequently varying amounts of that type of elements in Chromium, Nickel, Mo and V. If alloying elements other than carbon is here only in minute amounts as foe illustration: Mn upto 0.8 percent, Si upto 0.3 percent then the steel is commonly called as low alloy steel or plain carbon steel. Sulphur and phosphorus while more than 0.05 percent of also is there, tend to make steel brittle, hence during steel making these elements are decreased to at least such value. Si has slight effect on strength and ductility if less than 0.2 percent is there. As the content is raised to 0.4 percent the strength is raised with no effecting ductility, but above 0.4 percent Si, the ductility is impaired. Si is added as deoxidizer and that part that does not make silicon dioxide keeps in steel like impurity.
Mn is another alloying element such is there in most steels. Whether this exists in solid solution in the ferrite this has a strengthening effect. This may also exist in forms of Mn3C that forms part of the pearlite of MnS. Upto 1 percent of Mn has strengthening effects on steel and Mns presence in excess of 1.5 percent provokes brittleness in steel. Excess Mn is added to melt within steel making to bring its level to desired value. This acts also as a deoxidizer.
Intentional addition of a lot of other elements modifies the structure of steel and thus enhances its properties. Steels to such that intentional additions have been made as comprising those steel that have Mn in excess of 1 percent or Si in excess of 0.3 percent are termed as alloy steels. One exacting effect of alloying is which this enables martensite to be produced with low rates of cooling and permits larger sections to be hardened than is possible with plain carbon steel.
The significant elements that are utilizd to alloy along with steel in varying quantities are Nickel, Cr, Mo, W, Mn and Si. The bcc metals as Chromium, W and Mo while alloyed along with steel tend to form carbides that reduce the proportion of Fe3C in the structure. Conversely the fcc elements as Nickel, Al, Cu and Zr do not form carbides. Mn that has three allotropic difficult structures forms carbide also.
Various advantages in terms of enhanced mechanical properties and corrosion resistance are acquired by adding one or various alloying elements.