What is difference between Cast iron and Steel

Hi Pals,
Main difference between cast iron and steel is higher carbon and silicon content than steel.This difference in carbon content in cast iron and steel impart different properties to these two ferrous alloys.

Difference between Cast iron and Steel 

Cast Iron : Alloys of iron and carbon that contains Over  2% Carbon.

Steel : Alloys of iron and carbon that contains upto  2% Carbon.

CI is eutectic which contains majorly iron ,carbon,silicon and minor alloying elements.Due to higher carbon content it shows rich carbon phase i.e. graphite,Fe3C.Depending upon composition,cooling rate,melt treatment etc it solidifies to two systems.

1. Thermodynamically unstable Fe-Fe3C(Iron Cementite)
2. Stable Fe-Gr(Iron Graphite) 

Fist is when metastable solidification path is followed where rich carbon phase is  Fe3C.Second is when stable solidification path is followed where rich carbon phase is  graphite .

Steel is eutectic which contains iron,carbon with wide range of alloying elements also without alloying elements known as plain carbon steel.Carbon content is low in steels which require high ductility ,high toughness and good weldability. Carbon content is high in steels that require high strength ,hardness,fatigue resistance and wear resistance.

Difference between Cast iron and Steel classification

Classification of cast iron was based on fracture appearance.

White CI show white or bright fracture surface.
Gary CI iron show grayish fracture surface.

Classification based on graphite shape , lamellar/flake graphite,spheroidal/nodular graphite,compacted graphite, temper graphite

Classification based on matrix : Ferretic,perlitic,austenitic,martensitic,bainitic(austempered) 


Classification of steel can be variety of different systems
Composition : Carbon steel, low, medium,high carbon, stainless steel, tool steel.
Manufacturing methods : open hearth,basic oxygen,electric furnace method 
Finishing method : hot rolled , cold rolled.
Microstructure: Ferretic , pearlitic, masrtensitic 


Even if main difference between cast iron and steel is % of carbon content but some times some  alloying elements and silicon in CI change the maximum solubility of carbon in austenite. Therefore some alloy less than 2% carbon can belong to CI family.