Basic knowledge of metal heat treatment

Update:23 Sep 2019
Summary:

Metal heat treatment is a process in which a metal work […]

Metal heat treatment is a process in which a metal workpiece is heated to a suitable temperature in a certain medium and maintained at a constant temperature for a certain period of time.

Metal structure

 Metal: A substance that has opaque, metallic luster, good thermal conductivity and electrical conductivity, and whose electrical conductivity decreases with increasing temperature, and is characterized by ductility and ductility. The internal atoms of the metal have a regular arrangement of solids (ie, crystals).

 Alloy: A substance that has two or more metals or metals and non-metals and has metallic properties.

The components of the alloy with the same composition, structure and properties.

Solid solution: a solid metal crystal in which one (or several) elements of atoms (compounds) are dissolved in the lattice of another component while still maintaining the lattice type of another component, solid solution partitioned solid solution and replacement solid solution Two.

Solid solution strengthening: Since the solute atoms enter the gap or junction of the solvent lattice, the lattice is distorted, and the hardness and strength of the solid solution are increased. This phenomenon is called solid solution strengthening.

Compound: The alloying component is chemically combined to form a new crystalline solid structure with metallic properties.

Mechanical mixture: An alloy composition composed of two crystal structures, although it is a two-sided crystal, is a constituent with independent mechanical properties.

Ferrite: A gap solid solution of carbon in a-Fe (body-centered cubic iron).

Austenite: a gap solid solution of carbon in g-Fe (face-centered cubic iron).

Cementite: a stable compound (Fe3c) formed by carbon and iron.

Pearlite: a mechanical mixture of ferrite and cementite (F+Fe3c contains 0.8% carbon)

Leysite: a mechanical mixture of cementite and austenite (4.3% carbon)

Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing methods, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but changes the microstructure inside the workpiece or changes the chemical composition of the surface of the workpiece. , to give or improve the performance of the workpiece. It is characterized by improved intrinsic quality of the workpiece, which is generally not visible to the naked eye.