Carbon Steel
Carbon Steel
Carbon steel is an iron-carbon alloy with a carbon content less than 2.11%, which is the most common type of iron and steel material.
Its main Composition are iron and carbon, along with small amounts of elements such as silicon, manganese, sulfur, and phosphorus. Among them, silicon and manganese are beneficial elements that can increase the strength and hardness of steel. Silicon also has a deoxidizing effect; sulfur and phosphorus are harmful elements, with sulfur causing hot brittleness and phosphorus causing cold brittleness in steel.
Classification
- By carbon content:
– Low-carbon steel: The carbon content is less than 0.25%. It has relatively low strength but excellent plasticity, toughness, and welding performance. It is commonly used to manufacture products such as wire, rivets, steel pipes, and automobile bodies, which do not require high strength but need good processing properties.
– Medium-carbon steel: The carbon content ranges from 0.25% to 0.6%. It has higher strength and certain toughness. Through heat treatments like quenching and tempering, it can achieve good comprehensive mechanical properties. It is often used to make mechanical parts such as gears, shafts, and connecting rods.
– High-carbon steel: The carbon content is greater than 0.6%. This type of steel has high hardness and good wear resistance but poor plasticity and toughness. It is mainly used to manufacture springs, cutting tools, dies, and other tools that require high hardness and wear resistance.
- By quality (based on sulfur and phosphorus content):
– Common carbon steel: The sulfur content does not exceed 0.050%, and the phosphorus content does not exceed 0.045%. It has relatively poor quality and is generally used for structural components with low performance requirements.
– High-quality carbon steel: The sulfur content does not exceed 0.035%, and the phosphorus content does not exceed 0.035%. It has better performance and is used to manufacture more important mechanical parts.
– Superior high-quality carbon steel: The sulfur content does not exceed 0.025%, and the phosphorus content does not exceed 0.025%. It has high quality and is used to manufacture components with very high performance requirements.
Performance Characteristics
- Mechanical properties:
As the carbon content increases, the strength and hardness of carbon steel rise, while its plasticity and toughness decrease. Its mechanical properties indicators such as tensile strength and yield strength vary according to the carbon content and heat treatment state.
- Processing properties:
Low-carbon steel is easy to undergo hot working processes like forging and rolling, as well as cold working processes like cutting. Medium-carbon steel has good hot working performance but slightly poorer cold working performance. High-carbon steel has poor hot working performance and requires greater cutting force during cold working. However, its hardness can be significantly increased after quenching.
Heat Treatment Characteristics
- Annealing:
It can reduce the hardness of steel, improve its plasticity and toughness, and optimize the cutting performance.
- Normalizing:
It can refine the grain, adjust the hardness, and improve the cutting performance. The strength and hardness of carbon steel after normalizing are slightly higher than those after annealing.
- Quenching and tempering:
Quenching can significantly increase the hardness of steel, but it also makes the steel more brittle. Therefore, tempering is required to reduce the brittleness and balance the toughness and strength of the steel.
