Effect of Carbon on steel:
Increase in carbon in steel:
1) Decreases the ductility of steel.
2) Increases the tensile strength of steel
3) Increases the hardness of steel.
4) Decreases the ease with which steel can be machined.
5) Lowers the melting point of steel.
6) Makes steel easier to harden with heat treatments.
7) Lowers the temperature required to heat treat steel.
8) Increases the difficulty of welding steel.
Steel with 0.2% Carbon can attain Rockwell C hardness of 49, while an 0.8% carbon steel can be hardened to Rockwell C of 65.
As carbon is added, steel gets harder and becomes difficult to machine,
Melting point of 0.2% carbon steel is 2800°F while 0.8% carbon steel can melt near 2,700°F. Steel are classified according to their carbon content. Carbon will dissolve into iron without producing steel at 0.026% at 1330°F.
Low carbon steel or mild steel contain less than 0.3% carbon. Medium carbon steels contain carbon from 0.3 -0.55%. High carbon steel contain more than 0.5% carbon. Iron with more than 2% carbon is referred to as Cast Iron.
Steels for springs must have at least 0.45 % carbon to attain required hardness.
Plain Carbon steel such as 1045, 1060, 1074, 1080 or even 1095 can be used for springs but become rather brittle at higher carbon content. Plain carbon steel are used for flat springs. The alloyed steels such as 6150, 9260 and 8650 are recommended because of their added toughness. A 302 stainless steel is often used for springs that have higher temperature requirements.