What is the difference between iron and steel?
The actual chemistry of steel and iron is similar. Very simply, there is more carbon added to pure iron to produce cast iron. The additional carbon is converted in the microstructure to graphite. This graphite gives iron the natural chip breaking benefits that allow you to machine iron so much faster than steel. It also presents a ready reserve of carbon for heat treating of the part and makes it lighter.
Iron is an element, with atomic number 26. That means every iron atom has 26 protons, and how many neutrons it has depends on its isotope. Solid iron makes crystals with a regular lattice pattern, but iron crystals can have little defects in them — missing atoms, extra atoms, places where the regular lattice patterns don t match up quite right. Steel is made by adding a small amount (usually less than 2%) of carbon. Adding carbon helps prevent defects in the iron crystals from sliding around, and makes the iron stronger. Steel may have other ingredients added, to improve its properties: tensile strength, hardness, resistance to corrosion, elasticity, and other properties. Common ingredients are nickel, manganese, chromium, molybdenum, and vanadium. Stainless steel contains a lot of chromium (18%) and also quite a lot of nickel (8%), and is quite expensive.
Steel is Iron that has been infused with extra carbon. Imagen iron as an open framework of boxes. When it is heated up over coal, the framework expands and carbon molecules enter the frames, then when it is cooled the framework contracts trapping the carbon inside, the result is steel. Much more dense.
