Classification of steel

Steel is an alloy with iron and carbon as the 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: carbon steel (referred to as carbon steel) and alloy steel according to its chemical composition. Carbon steel is an alloy obtained by smelting 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 properties, 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 no longer fully meet the needs, so people have developed various alloy steels. Alloy steel is a multi-element alloy obtained by adding some elements (called alloying elements) purposefully on the basis of carbon steel. Compared with carbon steel, the performance of alloy steel has been significantly improved, so it is increasingly widely used.

Due to the wide variety of steel materials, in order to facilitate production, storage, selection and research, steel materials must be classified. According to different purposes, chemical composition and quality of steel, steel can be divided into many categories:

(1). Classification by purpose

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

1. Structural steel:

(1). Steel used for various machine parts. It includes carburized steel, quenched and tempered steel, spring steel and rolling bearing steel.

(2). Steel used for engineering structure. It includes A, B, special grade steel and ordinary low alloy steel in carbon steel.

2. Tool steel: steel used to manufacture various tools. According to different uses of tools, it can be divided into cutting tool steel, die steel and measuring tool steel.

3. Special performance steel: steel with special physical and chemical properties. Can be divided into stainless steel, heat-resistant steel, wear-resistant steel, magnetic steel, etc.

(2). 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 carbon content, it can be divided into low carbon steel (carbon content ≤0.25%); medium carbon steel (0.25%<carbon content<0.6%); high carbon steel (carbon content ≥0.6%) .

Alloy steel: According to the content of alloying elements, 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, according to the different types of main alloying elements contained in steel, it can also be divided into manganese steel, chromium steel, chromium nickel steel, chromium manganese titanium steel and so on.

(3). Classification by quality

According to the content of harmful impurities 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 contains sulfur Amount≤0.030%).

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

When naming steel products, steel mills often combine the three classification methods of use, composition, and quality. For example, the 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, etc. Are ≤0.040%); high-grade high-quality steel (phosphorus content ≤0.035%,