Plain carbon steel

Low-carbon steel: (less than 0.3%C)

—Good formability and weld ability but lack hardenability

—Used in hot-forming, cold-forming etc.

  Medium carbon steel or Mild steel (0.3% to 0.8 % carbon)

—high toughness & ductility

—Most widely used steel

—Heat treatable (austenitizing, quenching and tempering).

—Hardenability is increased by adding Ni, Cr, Mo.

—Used in various tempered conditions.

—Typical applications: gears, railway tracks, machine parts. 

  High carbon steel (more the 0.8 %C)

—Hardness & wear resistance  are high but  Toughness & formability is very low

  NoteÞ purest form of Iron i.e. wrought iron has least carbon content.