(a) Distinguish between plain carbon steel and alloy steel.
(b) How the mechanical properties of an untreated plain carbon steel are influenced by increase in the carbon content ?
(a) Plain carbon steel is one which owes its distinctive properties chiefly to the carbon it contains.
An alloy steel is one which owes its distinctive properties chiefly to some element or elements other than carbon, or jointly to such other elements and carbon. The other elements are deliberately introduced in alloy steel to confer special properties.
(b) The tensile strength of untreated plain carbon steel increases roughly linearly from about 35 kgf/mmo at 0.05% carbon to about 90 kgf/mm2 at 0.9% carbon. The hardness value increases roughly linearly from about HB 100 at 0.05% carbon to about HB 200 at 0.9% carbon. Ductility (measured by an elongation value) decreases with increase in the percentage of carbon. Malleability (measured by reduction in area) decreases with increase in percentage of carbon