PLAIN CARBON STEEL


The term steel usually means an iron-based alloy containing carbon in amounts about <2%.
The plain carbon steel is also known as 'Carbon steel' or 'Ordinary steel'.

Plain carbon steel can defined as metal mainly containing Fe, C and residual amount to other elements like Al, Si, Mn, S, P, O.

These elements are not added for specific purpose but they are inevitably present due to iron and steel making processes and can not be completely removed.

Removal of these materials increases the cost that's why in case of cheaper variety of steels contents are tolerated.
These tolerable limits of impurities are called 'Safe limits' and they are decided such that it do not effect the properties of steel.

-Plain carbon steels are mainly sub-divided into four groups.


Name % Content
1 Low Carbon Steel Upto 0.15 % C
2 Mild carbon steels 0.15 - 0.35 %C
3 Medium carbon steel 0.35 - 0.65 %C
4 High carbon steel 0.65 - 1.75 %C

- Materials classified as carbon steel might also contain small amounts of other elements, such as Cr, Ni, Mo, Cu, V, Ni, P, S. The alloying additions are responsible for many of the differences between the various types or grades of carbon steels.

1) Carbon [C]

  • Upto 2% in steel.
  • Below 0.5% in welded steel.
  • Most important alloying element in steel.
  • Carbon can be present in two forms. Dissolved form or combined form such as cementite (Fe3C).
  • Pros = Increase in carbon content increases hardness, tensile strength, hardenability.
  • Cons = Increase in carbon content decreases weldability.
2) Manganese [Mn]
  • Atleast 0.3% in steel.
  • Around 1.5% in carbon steels.
  • Helps in deoxidation of steel.
  • Prevents formation of iron-sulphide inclusions.
  • Increases hardenability. 
3) Silicon [Si]
  • Upto 1% in steel castings.
  • Used as de-oxidizer.
  • Increases metal strength and reduces ductility.
4) Sulfur [S]
  • It is an undesired material in steel.
  • >0.05% sulfur increases brittleness and decreases weldability.
  • Amounts of 0.1-0.3 % improves machinability.
5) Phosphorus [P]
  • It is an undesired material in steel.
  • Generally content is 0.04% in steel.
  • It is added in amounts of  0.1% improves corrosion resistance.
6) Chromium [Cr]

  • Its an powerful element in alloying of steel.
  • It increases hardenability and improves corrosion resistance.
  • Stainless steel contains >12% of chromium.

7) Molybdenum [Mo]

  • Present <1.0% in steel.
  • It is a strong carbide former.
  • It increases strength at higher temperature.
8) Nickel [Ni]
  • Improves toughness and ductility of steel.
  • Also increases hardness and strength.
  • It improves steel toughness at low temperatures.
9) Vanadium  [V]
  • Alloying of  >0.05% makes material  embrittled.
  • It increases hardenability of steel.