What is the principal difference between steel and cast iron?

What is the principal difference between steel and cast iron?

• A. Manufacturing method
• B. Carbon content
• C. Corrosion resistance
• D. Thermal conductivity

Answer: (B)

The main thing that sets steel apart from cast iron is how much carbon is in the metal. Steel has a relatively low carbon content, typically well under 2%, which gives it a ductile, tough, and weldable character. Cast iron, on the other hand, contains a higher carbon content (above about 2.1%), and this extra carbon changes the structure—often forming graphite or cementite—making cast iron harder but more brittle. This carbon-driven difference explains why steel can be shaped and don’t fracture as easily under bending, while cast iron is excellent for casting and wear resistance but less forgiving to impact. The other factors listed can vary independently of this fundamental distinction, so they don’t define the difference as clearly.

The main thing that sets steel apart from cast iron is how much carbon is in the metal. Steel has a relatively low carbon content, typically well under 2%, which gives it a ductile, tough, and weldable character. Cast iron, on the other hand, contains a higher carbon content (above about 2.1%), and this extra carbon changes the structure—often forming graphite or cementite—making cast iron harder but more brittle. This carbon-driven difference explains why steel can be shaped and don’t fracture as easily under bending, while cast iron is excellent for casting and wear resistance but less forgiving to impact. The other factors listed can vary independently of this fundamental distinction, so they don’t define the difference as clearly.