Today I will talk about the specific classification of carbon steel

Classified by chemical composition

Carbon steel can be divided into low-carbon steel, medium-carbon steel, and high-carbon steel according to chemical composition (that is, carbon content).

(1) Mild steel

Also known as mild steel, low carbon steel with carbon content ranging from 0.10% to 0.25% is easy to accept various processing such as forging, welding, and cutting. It is often used to make chains, rivets, bolts, shafts, etc.

(2) Medium carbon steel

Carbon steel with a carbon content of 0.25% to 0.60%. There are a variety of products such as killed steel, semi-killed steel, and boiling 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, but poor welding performance. Strength and hardness are higher than low carbon steel, while 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. The quenched and tempered medium carbon steel has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55 (HB538), and σb is 600-1100MPa. Therefore, medium-carbon steel is the most widely used in various applications of medium strength level. In addition to being used as a building material, it is also widely used in the manufacture of various mechanical parts.

(3) High carbon steel

Often called tool steel, the carbon content ranges from 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, and reamers are made of steel with a carbon content of 0.90% to 1.00%.

Classified by steel quality

According to the quality of steel, it can be divided into ordinary carbon steel and high-quality carbon steel.

(1) Ordinary carbon structural steel, also known as ordinary carbon steel, has wider restrictions on carbon content, performance range, and phosphorus, sulfur, and other residual elements. In China and some countries, it is divided into three categories according to the guarantee conditions of delivery: Class A steel (Class A steel) is steel that guarantees mechanical properties. Class B steel (Class B steel) is steel with guaranteed chemical composition. Special steel (C steel) is steel that guarantees both mechanical properties and chemical composition and is often used to manufacture more important structural parts. China currently produces and uses A3 steel (Class A No. 3 steel) with a carbon content of about 0.20%, which is mainly used for engineering structures.

Some carbon structural steels also add a small amount of aluminum or niobium (or other carbide-forming elements) to form nitride or carbide particles to limit the growth of grains, strengthen the steel, and save steel. In China and some countries, in order to meet the special requirements of professional steel, the chemical composition and performance of ordinary carbon structural steel have been adjusted, thereby developing a series of professional steels (such as bridges, buildings, Steel bars, steel for pressure vessels, etc.).

(2) Compared with ordinary carbon structural steel, high-quality carbon structural steel has a lower content of sulfur, phosphorus, and other non-metallic inclusions. According to the different carbon content and use, this type of steel can be roughly divided into three categories: ① Less than 0.25%C is low-carbon steel, especially 08F, 08Al with carbon content less than 0.10%, etc., due to its good depth Punching and weldability are widely used as deep-drawn parts such as automobiles, cans... etc. 20G is the main material for making ordinary boilers. In addition, low carbon steel is also widely used as carburizing steel for machinery manufacturing. ②0.25～0.60%C is medium carbon steel, which is mostly used in the quenched and tempered state to make parts for the machinery manufacturing industry. ③High carbon steel greater than 0.6% C is used to make springs, gears, rolls, etc. According to the difference of manganese content, it can be divided into two steel groups, ordinary manganese content (0.25-0.8%) and higher manganese content (0.7-1.0% and 0.9-1.2%). Manganese can improve the hardenability of steel, strengthen ferrite, and increase the yield strength, tensile strength, and wear resistance of steel. Usually, “Mn” is added after the steel grade with high manganese content, such as 15Mn, 20Mn, to distinguish it from carbon steel with normal manganese content.

Classified by purpose

According to its purpose, it can be divided into carbon structural steel and carbon tool steel.

The carbon content of carbon tool steel is between 0.65 and 1.35%. After heat treatment, high hardness and high wear resistance can be obtained. It is mainly used to manufacture various tools, cutting tools, dies, and measuring tools (see tool steel).

Carbon structural steel is divided into 5 grades according to steel yield strength:

Q195, Q215, Q235, Q255, Q275

Each grade is divided into A, B, C, D grades due to different quality. There are four at most, and some have only one. In addition, there are differences in deoxidation methods for steel smelting.

Symbol of deoxygenation method:

F-boiling steel

b——Semi-killed steel

Z-killed steel

TZ——Special Killed Steel