The Introduction of Structure of Steel Materials
Steel material is a kind of metal material. It has a series of excellent properties such as strength, plasticity, processibility, wear resistance and high temperature resistance. In general, the steel refers to an alloy composed of iron, carbon and one or several other alloying elements. According to microstructure, steel can be divided into ferrite and pearlite.
The structure of steel has an important influence on the performance of steel. The structure of steel includes two levels: macrostructure and microstructure. Macrostructure includes hot rolled, cold-rolled and hot-working three parts, of which hot rolled steel is usually divided into semi-killed steel and killed steel according to the amount of steel deoxidation. According to different manufacturing process, the macrostructure of steel can also be divided into ingot steel and continuously cast steel.
The microstructure of steel refers to the physical state of the steel materials at atomic and molecular level, which determines the properties of the steel materials. The microstructure of steel is generally composed of austenite grains and pearlite, ferrite and other components, and sometimes with fibers, cementite, carbides and other components.
Generally speaking, when the temperature of the steel is lower than the A3 point (about 727℃), its microstructure is ferrite and pearl. The ferrite has a body-centered orthorhombic crystal structure, and the pearlite is an alternation of ferrite and cementite, and its crystal structure is a matrix structure of ferrite and cementite.
The microstructure of steel materials will change significantly as the heat treatment process changes. Through different heat treatment process, the volume proportion of ferrite and pearlite can be changed, and the internal forms of ferrite and pearlite and their relationship distribution can also be changed.
At the same time, in the heat treatment process, carbides, fiber and other components may be generated. Fiber is generated when austenite is cooled above A1 point (about 900℃). During the quenching process, the formation of cementite can cause the microstructure of steel materials to form fine carbides, which can make the steel material perform more excellent plasticity and wear resistance.
In addition, quenching and tempering can also make the internal structure of steel material more uniform, reduce microstructure segregation and brittle-like inter- or sub-surface layered structure, and further improve the plasticity and toughness of certain steel materials.
In summary, the structure of steel is the most important factor influencing the performance of steel materials. Different microstructure and macrostructure of steel materials determine the properties of the steel materials to a large extent. Therefore, it is of great importance to choose reasonable steel structure for heat treatment of steel materials and control reasonable heat treatment process.
