Iron

• Iron is the basis of all steel. Iron is dug from the Earth as ore and then transported to a mill where it's cleaned and fed into a blast furnace. The furnaces reach such high temperatures that the iron is melted, becoming a pool of liquid iron that is denser than the impurities, which float to the top in the form of slag. The slag is siphoned off so what's left is pure iron.
  
  

Carbon

• Steel is iron combined with carbon, typically less than 1 percent. Carbon primarily comes in the form of coke, which is a product made from coal. The coke is added into the blast furnace, and as the coke burns, the carbon from the gas that's created is absorbed into the iron, which, through a chemical process, will turn the iron into steel.
  
  

Chromium

• Chromium is a material uses only when making stainless steel. The chromium content is what accounts for the shine of stainless steel, but it's also what makes it immune to oxidation, providing resistance to rust and chemical change over time. It needs to be added in proper amounts based on the amount of steel you want stainless, which needs to be carefully determined before hand.
  
  

Limestone

• Limestone is the third component used for making basic steel. When the coke and iron and put into the blast furnace the limestone is added. The limestone breaks down and the silicates in the limestone bond to the slag and help it rise even faster. The limestone's purpose is to help sort the iron from impurities so as little slag gets into the final product as possible.