Common classification of steel

There are many ways to classify commonly used steel forgings, usually according to its chemical composition, use, smelting method and metallographic structure. No matter what kind of classification method is adopted, we must adhere to the principle of "scientific and practical" and choose a reasonable classification method from the actual needs. Usually, in order to scientific research needs, according to chemical composition classification; For ease of use. More classified by use; In order to facilitate management, according to the smelting method classification; In order to check the needs of the work, according to the metallographic organization classification. Because of the different classification methods, the same steel number can be divided into different categories. For example, GCRL No. 5 steel, according to the chemical composition classification, because chromium as the main alloy element, can be divided into chromium steel; Classified by use, because it is mainly used to manufacture bearings, it can be divided into high carbon chromium bearing steel; According to the smelting method classification, the steel can be divided into: with converter smelting called converter steel, with electric furnace smelting called electric furnace steel. Smelting with open furnace is called open furnace steel; According to the classification of metallographic structure, the microstructure of the steel after normalizing treatment is pearlite, which can be divided into pearlite steel. Because the microstructure of the annealed steel is granular pearlite with excess carbide, it can also be divided into eutectoid steel.

1. Classification by chemical composition

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

Carbon steel is mainly composed of iron and carbon. In addition, the steel also contains manganese, silicon, sulfur, phosphorus and other elements. Among them, sulfur and phosphorus are harmful impurities; Manganese and silicon are the elements that need to be deoxidized and added in the process of steel making.

According to the different carbon content in carbon steel, it can be divided into the following three kinds:

Low carbon steel: carbon content is 0.04% 0.25%;

Medium carbon steel: 0.25% carbon content

High carbon steel: carbon content above 0.55%.

Alloy steel is steel made by adding one or more alloying elements to carbon steel. This steel contains not only silicon and manganese as alloying elements or deoxidation elements, but also other alloying elements, such as chromium, nickel, molybdenum, vanadium, titanium, tungsten, aluminum, cobalt, niobium, zirconium, rare earth gold, etc. In addition, some alloy steels also contain some non-metallic elements, such as boron, nitrogen, calcium and so on. According to the total amount of alloy elements contained in steel, it can be roughly divided into the following three kinds:

The total alloying element content of low alloy steel is less than 3.5%;

The total content of alloy elements in medium alloy steel is 3.5% 10%;

The total alloying element content of high alloy steel is higher than 10%.

Alloy steel can also be divided into two, three and multiple alloy steel according to the number of alloying elements it contains. In addition, according to the types of alloy contained in steel, it can also be generally divided into manganese steel, chromium steel, boron steel, silicon manganese steel, chromium manganese molybdenum steel, chromium molybdenum vanadium tungsten steel and so on.

2. Categorize by use

Classification of steel by use is the main method of steel classification. China Metallurgical Industry Standard (YB) and National Standard (GB) - are formulated according to the classification of steel use.

According to the different uses of industrial steel, can be divided into structural steel, tool steel, special purpose steel three.

Structural steel is mainly used in buildings, Bridges, ships, vehicles, boilers and other building structures and mechanical parts. According to its specific use, it can be subdivided into carbon structural steel, low alloy structural steel, high quality carbon structural steel, alloy structural steel, etc.

Tool steel is generally used to manufacture tools such as cutting tools, measuring tools and molds. Tool steel includes carbon tool steel, alloy tool steel and high speed tool steel. Alloy tool steel is often divided into measuring tool steel, impact tool steel, cold working die steel, hot working die steel, non-magnetic die steel and plastic die steel, etc.

Special purpose steels generally have specific properties. For example, stainless steel can resist corrosion in air, acid resistant steel can resist acid corrosion in some chemical etching media, heat resistant steel has good oxidation resistance at high temperature, and has certain creep resistance and break energy resistance, silicon steel has good electromagnetic properties, which is specially used in the electrical appliance manufacturing industry.

In addition, there are spring steel and high carbon chromium bearing steel. Spring steel is generally classified as structural steel according to its carbon content. But because of its unique heat treatment process, it is usually classified as special purpose steel. High carbon chromium bearing steel belongs to tool steel in terms of its chemical composition. But from the point of view of use, because it is specially used to manufacture bearings, it should also belong to special steel.