Steel is a materials composed primarily of iron. Most steel contains more that 90% iron. Many types of carbon steel contains more that 99% iron. All types of steel contains a second element – carbon. Many other alloying elements are used in most steel, but iron and carbon are the only elements found in all steel.
a) In steel, the iron dissolves the carbon
b) In gray cast iron, the precipitates out as carbon flakes
c) In ductile cast iron, the carbon precipitates out as small round modules.
Figure: Microstructural views of steel and cast iron.
The percentage of carbon in steel ranges from just above 0% to approximately 2%. Most steel has between 0.15% and 1.0% carbon. Steel with less carbon is more flexible (ductile) that high-carbon steel, but it is also weaker. As the carbon content increases, so do strength and brittleness. When steel is made, the iron dissolves the carbon. When there is too much carbon for the iron to digest, the resulting alloys is no longer called. The carbon precipitates out and remains in the of flakes or other shapes as shown by Figure above. Approximately 2% carbon is the most that can dissolved in the iron.