Classification of carbon steel

1. According to the mass percentage of carbon:
Low carbon steel (C: ≤0.25%) Also known as mild steel, low carbon steel is easy to accept various processing such as forging, welding and cutting, and is often used to make chains, rivets, bolts, shafts, etc.

Medium carbon steel (C: 0.25%<C ≤ 0.6%) has various products such as killed steel, semi-killed steel, and ebullient steel. In addition to carbon, it can also contain a small amount of manganese (0.70% to 1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. Good thermal processing and cutting performance, poor welding performance. The strength and hardness are higher than low carbon steel, but the plasticity and toughness are lower than low carbon steel. Hot-rolled and cold-drawn materials can be used directly without heat treatment, or after heat treatment. Medium carbon steel after quenching and tempering has good comprehensive mechanical properties. The highest hardness that can be achieved is about HB538, and the tensile strength σb is 600-1100MPa. Therefore, in various uses of medium strength level, medium carbon steel is the most widely used. In addition to being used as building materials, it is also widely used in the manufacture of various mechanical parts.

High carbon steel (C: >0.6%) is often called tool steel, with a carbon content from more than 0.60% to 1.70%, which can be hardened and tempered. Hammers, crowbars, etc. are made of steel with a carbon content of 0.75%; cutting tools such as drills, taps, reamers, etc. are made of steel with a carbon content of 0.90% to 1.00%. The higher the carbon content, the greater the hardness and strength, but the lower the plasticity (In addition, iron-carbon alloys with a carbon content of 2.1% to 4.5% are generally called cast iron.)

2. According to the metallurgical quality of steel (mainly the content of impurities sulfur and phosphorus):

Ordinary carbon steel (S ≤0.055%, P ≤0.045%)

High quality carbon steel (S ≤0.040%, P ≤0.040%)

High quality carbon steel (S ≤0.030%, P ≤0.035%)

3. According to the purpose:
Carbon structural steel: mainly used in bridges, ships, building components, machine parts, etc.

Carbon tool steel: mainly used for knives, molds, measuring tools, etc.