Final answer:
The steel resulting from adding up to 0.8% carbon to iron and under equilibrium conditions will have a pearlite microstructure, consisting of ferrite and cementite in a body-centered cubic lattice, commonly known as mild steel.
Step-by-step explanation:
When up to 0.8% carbon is added to iron, the resulting steel under equilibrium conditions will have a microstructure known as pearlite. Pearlite is a mixture of two phases: ferrite and cementite (iron carbide). Ferrite is a body-centered cubic (BCC) form of iron which exists below 910 °C and is relatively soft. The structure of this low-temperature form of iron is body-centered cubic, with one-eighth of an atom at each of the eight corners of the cube and one atom in the center of the cube. Cementite is a hard and brittle intermetallic compound that, when interspersed with ferrite layers, gives the steel its strength and hardness. Steels with a carbon content of up to about 0.8% are often referred to as mild steel and are used in a wide range of applications due to their ductility and toughness.