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Classification of steel

2019-05-13

Steel is an alloy containing iron and carbon as its main components, and its carbon content is generally less than 2.11%. Steel is an extremely important metal material in economic construction.

Steel is divided into two categories according to its chemical composition: carbon steel (carbon steel for short) and alloy steel. Carbon steel is an alloy obtained from smelting of pig iron. In addition to iron and carbon as its main components, it also contains a small amount of impurities such as manganese, silicon, sulfur and phosphorus. Carbon steel has certain mechanical properties, good process performance, and low price. Therefore, carbon steel has been widely used. However, with the rapid development of modern industry and science and technology, the performance of carbon steel can not fully meet the needs, so people have developed a variety of alloy steel. Alloy steel is a multi-component alloy obtained by preferentially adding certain elements (called alloying elements) on the basis of carbon steel. Compared with carbon steel, the performance of alloy steel is significantly improved, so it is increasingly used.

Due to the wide variety of steels, steel must be classified for ease of production, storage, selection and research. Steel can be divided into many categories according to the use, chemical composition and quality of steel:

One. Classified by purpose

According to the use of steel, it can be divided into three categories: structural steel, tool steel and special performance steel.

Structural steel: 1. Steel used as various machine parts. It includes carburized steel, quenched and tempered steel, spring steel and rolling bearing steel.

2. Used as steel for engineering structures. It includes A, B, special steel and ordinary low alloy steel in carbon steel.

Tool steel: Steel used to make various tools. According to the use of tools, it can be divided into cutting tool steel, die steel and measuring steel.

Special performance steel: It is a steel with special physical and chemical properties. Can be divided into stainless steel, heat-resistant steel, wear-resistant steel, magnetic steel and so on.

two. Classified by chemical composition

According to the chemical composition of steel, it can be divided into two categories: carbon steel and alloy steel.

Carbon steel: According to the carbon content, it can be divided into low carbon steel (carbon content ≤0.25%); medium carbon steel (0.25%

Alloy steel: According to the alloying element content, it can be divided into low alloy steel (total content of alloying elements ≤ 5%); medium alloy steel (total content of alloying elements = 5% -10%); high alloy steel (total content of alloying elements > 10%). In addition, depending on the type of main alloying elements contained in the steel, it can also be classified into manganese steel, chrome steel, chrome-nickel steel, chromium-manganese-titanium steel, and the like.

three. Classified by quality

According to the content of harmful impurities such as phosphorus and sulfur in steel, it can be divided into ordinary steel (phosphorus content ≤0.045%, sulfur content ≤0.055%; or phosphorus and sulfur content ≤0.050%); high quality steel (phosphorus and sulfur content ≤ 0.040%); high-quality steel (phosphorus content ≤0.035%, sulfur content ≤0.030%).

In addition, according to the type of smelting furnace, the steel is divided into open hearth steel (acid flat furnace, alkaline open hearth furnace), air converter steel (acid converter, alkaline converter, oxygen top-blown converter steel) and electric furnace steel. According to the degree of deoxidation during smelting, the steel is divided into boiling steel (incomplete deoxidation), killed steel (complete deoxidation) and semi-killed steel.

When steel mills name steel products, they often combine the three classification methods of use, composition and quality. For example, steel is called ordinary carbon structural steel, high-quality carbon structural steel, carbon tool steel, high-quality carbon tool steel, alloy structural steel, alloy tool steel and so on.

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