Difference Between Steel and Cast Iron

Steel vs Cast Iron

Steel and Cast iron are iron alloys in which the main alloying element is carbon. These alloys are used in many applications due to their increased desirable properties. One of the increased properties of steel and cast iron is that they are harder than iron. Presence of carbon causes the high hardness. These alloys are subjected to heat treatments to impart desired properties. In iron-carbon alloys, carbon can exist in the forms of iron carbide and graphite. These forms and the different percentages of carbon vary the properties of the alloy.

Steel

In steel, the main alloying element is carbon, and the other elements are Manganese, Silicon and Copper. Steel contains up to 2% carbon, up to 1.65% Manganese, up to 0.6% Silicon, and up to 0.6% copper by weight. Steel is classified into low carbon steel, medium carbon steel, high carbon steel, and tool steel depending on the percentage of carbon in steel. In steel, carbon is present as iron carbide. Steel is harder than iron, but because of the ductility in steel, it has the ability to be changed to different shapes by the application of forces. Steel melts at temperatures between 1325oC and 1530oC.

Cast Iron

Cast iron contains 2- 4% of carbon by weight. In cast iron, a higher silicon concentration (1-3% by weight) and a greater concentration of impurities are present. As a result, cast irons are also regarded as Fe-C-Si alloys. Cast irons can be easily cast into desired shapes on account of their higher fluidity, but cannot be worked due to brittleness. In cast iron, the presence of carbon is in the form of graphite or iron carbide or both. The form which carbon acquires is determined by the cooling rate during solidification, the influence of other alloying elements, and heat treatments. The melting point of cast iron ranges between 1130- 1250oC. Cast irons are classified into white cast iron, grey cast iron, malleable cast iron, nodular cast iron, and high alloy cast iron depending on their composition and structure.

What is the difference between Steel and Cast Iron?

Cast iron is cheaper than most steels. In addition, the melting temperature of cast iron is lower compared with steel, and cast iron has high compressive strength, high hardness and high wear resistance. Steel is ductile and malleable. Applications of steel are for cookware, blades, bridges, cars, engines, railway tracks, etc. Car parts, cylinder blocks, gear boxes, cookware, etc are applications of cast iron. Both steel and cast iron have good resistance to corrosion.

In a nutshell, Cast Iron vs Steel

• Steel contains less than 2% carbon; cast iron contains more than 2% carbon by weight.

• Steel is ductile and malleable; cast iron is hard and has high compressive strength.

• The main alloying element of steel is Carbon with the Silicon percentage up to 0.60% by weight. In cast iron, the main alloying elements are carbon and Si (1-3%by weight).

• The form of carbon present in steel is iron carbide; in cast iron carbon is present as graphite or iron carbide or both.

• The melting point of cast iron is lower than steel.

• Cast iron has excellent fluidity, which steel does not have.