Metal heat treatment process

Metal heat treatment is a process that heats the metal to a certain extent and holds it for a period of time, and then cools it down in different ways and at different speeds. In summary, the heat treatment process is divided into three steps: heating, insulation and cooling.

Metal heat treatment can change the surface or internal crystal structure of the metal, thereby obtaining metal materials with different properties to meet the needs of industrial production.

The most basic heat treatment processes include annealing, normalizing, quenching, tempering, etc. Metals can obtain different microstructures through different processes, and their mechanical properties will also change. Therefore, understanding these four basic heat treatments will help us adjust and change the properties of materials to meet production needs.

Annealing: During annealing, the metal is heated to a certain temperature, and then cooled in the furnace or cooled in the ash. The main purpose of this is to soften the metal, reduce hardness, and improve plasticity; homogenize the internal microstructure of the material and refine the grains; and eliminate internal stress in the metal and work hardening. In industrial production, we mainly use annealing to eliminate residual stress in forgings, castings, hot-rolled parts, and cold-drawn parts to avoid deformation or fracture of these workpieces.

Normalizing: Heat the metal to a certain temperature, hold it for a period of time, and then take out the furnace and cool it in air. The main feature is that the cooling speed is lower than that of quenching but faster than that of annealing. Normalizing can improve the hardness of the material, refine the grains, remove the internal stress of the metal blank, and avoid cracking; normalizing can be used instead of quenching to reduce the deformation of the steel parts or prepare for subsequent quenching processing; it can eliminate the overheating effect caused by quenching, which is easy to quench again; it can improve the wear resistance of the casting, etc.

Quenching: Quenching heats the metal and then cools it rapidly. This can greatly improve the hardness, toughness, wear resistance and fatigue strength of the metal, meeting the requirements of most industrial production. Therefore, it has a wide range of applications, such as chemical machinery, petroleum machinery, Processing machine tools, aircraft and other parts are inseparable from the quenching process.

Tempering: Heating the martensite, that is, the quenched metal, to a certain temperature, and then using water, oil, air and other media to cool it at a suitable temperature. The purpose is to reduce the residual stress in the internal organization of the material, and adjust the hardness, strength, plasticity and toughness of the material by adjusting the heating temperature range. Different heating temperatures can obtain different effects. Therefore, the application range of tempering includes high hardness and low brittleness Cutting tools, molds, etc.; also includes springs, forging dies, etc. with high hardness and high elasticity; it also includes force-bearing structural parts with good comprehensive mechanical properties, such as connecting rods, bolts, gears, etc.

The above are the four most basic metal heat treatment processes. Usually in industrial production, we will perform multiple different heat treatments according to the performance requirements of the parts. For example, bolts can be quenched and tempered (that is, quenched and then tempered at high temperatures). The general heat treatment process for springs is quenching and medium temperature tempering, and the general heat treatment process for measuring tools is quenching and low temperature tempering, etc., to ensure that the final product meets the requirements.