Why is steel stronger than iron?

Answer: Carbon added makes it harder

Steel heated to higher temperature — Wrong. While heat treatment affects steel properties, strength comes from carbon addition. Pure iron is relatively soft. Adding small amounts of carbon (0.2-2%) creates steel, where carbon atoms strengthen the iron crystal structure, making it much harder and stronger.

Carbon added makes it harder ✓ — Correct! Steel is iron with added carbon (typically 0.2-2%). Carbon atoms fit into iron's crystal structure, preventing layers from sliding past each other—making steel much harder and stronger than pure iron. Different carbon levels and heat treatments create steels with different properties (mild steel, tool steel, stainless steel).

Compressed under extreme pressure — Wrong. While pressure can affect metal properties, steel's strength comes from carbon addition. Carbon atoms in iron's crystal lattice prevent deformation, creating a harder, stronger material than pure iron.