1. Carbon steel is steel in which the main interstitial alloying constituent is carbon in the range of 0.12–2.0%.The term “carbon steel” may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels.
2. The American Iron and Steel Institute (AISI) defines carbon steel as the following:
“Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60.”
3. As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weld-ability. In carbon steels, the higher carbon content lowers the melting point.
4.The majority of the nearly 3, 500 different types of steel produced and available in the global market today is carbon steel. Carbon steel is formed when two elements, iron and carbon, is combined with carbon being used as the alloying element. The carbon is used as a hardening agent to prevent iron atoms in the crystal lattice from sliding around. The carbon steel structure also has ferrite, pearlite and cementite present in varying quantities, depending on the carbon quantity of the steel.
5. The percentage of carbon in the steel affects the hardness, strength elasticity and ductility of the steel. Low carbon content steel or mild steel has similar properties to iron but it is softer and easy to form.
6. As the carbon content rises, the steel is harder and stronger but it is less ductile.
- Mild or low carbon steel has a carbon content of 0.05 to 0.26 percent,
- Medium carbon steel has a carbon content of 0.29 to 0.54 percent,
- High carbon steel has a carbon content of 0.55 to 0.95 percent with very high carbon steel having a carbon content of 0.96 to 2.1 percent.
MILD AND LOW CARBON STEEL
1. Mild steel, also called plain-carbon steel, is the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications.
2. Low carbon steel contains approximately 0.05–0.15% carbon and mild steel contains 0.16–0.29% carbon; making it malleable and ductile, but it cannot be hardened by heat treatment.
3. Mild steel has a relatively low tensile strength, but it is cheap and malleable; surface hardness can be increased through carburizing.
4. It is often used when large quantities of steel are needed, for example as structural steel. The density of mild steel is approximately 7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3) and the Young’s modulus is 210 GPa (30,000,000 psi).
5. Low carbon steels suffer from yield-point runout where the material has two yield points. The first yield point (or upper yield point) is higher than the second and the yield drops dramatically after the upper yield point
6. If a low carbon steel is only stressed to some point between the upper and lower yield point then the surface may develop Lüder bands.
7. Low carbon steels contain less carbon than other steels and are easier to cold-form, making them easier to handle.
8. Mild steel typically has a maximum of 0.25% Carbon and 0.4%-0.7% manganese, 0.1%-0.5% Silicon and some + traces of other elements such as phosphorous,it may also contain lead (free cutting mild steel) or sulphur (again free cutting steel called re-sulphurised mild steel)
HIGH CARBON STEEL
1. High carbon steel will be any type of steel that contains over 0.8% carbon but less than 2.11% carbon in its composition. The average level of carbon found in this metal usually falls right around the 1.5% mark.
2. High carbon steel has a reputation for being especially hard, but the extra carbon also makes it more brittle than other types of steel. This type of steel is the most likely to fracture when misused
3. High carbon steel remains popular for a wide variety of uses. This type of steel is preferred in the manufacturing of many tools such as drill bits, knives, masonry nails, saws, metal cutting tools, and woodcutting tools.
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