What are the classifications of carbon steel?

Carbon steel has a variety of classification methods, such as according to the chemical composition (that is, by carbon content) can be divided into low carbon steel, medium carbon steel and high carbon steel. According to the quality of steel can be divided into ordinary carbon steel and high quality carbon steel. According to the use can be divided into carbon structural steel, carbon tool steel. In addition, it can also be classified by smelting method and guaranteed performance requirements.

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

Some carbon structural steel also add trace aluminum or niobium (or other carbide forming elements) to form nitride or carbide particles, in order to limit grain growth, strengthen steel, save steel. In China and some countries, in order to meet the special requirements of professional steel, the chemical composition and properties of ordinary carbon structural steel have been adjusted, thus developing a series of ordinary carbon structural steel for professional use (such as bridge, construction, rebar, pressure vessel steel, etc.). [2]

Classification by carbon content

1) less than 0.25%C is low carbon steel, especially with carbon less than 0.10% of the 08F, 08Al, because of its good deep drawing and weldability and widely used as deep drawing parts such as automobiles, canmaking, 20G is the main material for the manufacture of ordinary boilers, in addition, low carbon steel is also widely used as carburizing steel, used in machinery manufacturing.

2) 0.25 ~ 0.60%C is medium carbon steel, mostly used in the condition of tempering, making parts in the machinery manufacturing industry.

3) Higher than 0.6%C is high carbon steel, which is mostly used to manufacture springs, gears, rolls, etc. According to the different manganese content, it can be divided into 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, improve the yield strength, tensile strength and wear resistance of steel. Usually, "Mn" is added after the grade of steel with high manganese content, such as 15Mn and 20Mn, to distinguish it from carbon steel with normal manganese content.

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

When the carbon content is 2.11%, it is the golden section point between cast iron and carbon steel. Carbon steel before 2.11%. The carbon content after 2.11% is cast iron. The carbon content between 0.0218% and 0.77% is called hypoeutectoid steel and 0.77% to 2.11% is called hypereutectoid steel. Eutectoid steel with carbon content of 0.77%. If the carbon content is between 2.11% and 4.3%, it is called subeutectic white cast iron, and if the carbon content is between 4.3% and 6.69%, it is called hypereutectic white cast iron. Eutectic white cast iron with carbon content of 4.3%. [2]

Classified according to the form existing in cast iron

According to the different forms of carbon present in cast iron, cast iron can be divided into: White cast iron (most of the carbon exists in the form of carburite in cast iron), gray cast iron (most of the carbon exists in the form of flake graphite), malleable cast iron (made of white cast iron after graphitization annealing, in which the carbon exists in the form of flocculent graphite) and nodular cast iron (after spheroidization treatment before pouring, the carbon exists in the form of spheroidal or clumped graphite.