Heat treatment annealing
Time：2022-05-09 Author：Material scientific research service platform
Heat treatment annealing is a combination of heating and cooling operations on a metal or alloy to achieve desired properties. The annealing process requires the material to remain above its recrystallization temperature for a certain period of time before cooling. The cooling rate depends on the type of metal being annealed. For example, ferrous metals such as steel are usually cooled to room temperature in still air, while copper, silver and brass can be cooled slowly in air or rapidly quenched in water. The heating process causes atoms to migrate in the lattice and reduce the number of dislocations, resulting in changes in ductility and hardness. Heat-treated materials recrystallize upon cooling, and grain size and phase composition depend on heating and cooling rates, which in turn determine material properties. Hot or cold working the metal after annealing changes the material structure again, so further heat treatment may be required to achieve the desired properties.
The working principle of heat treatment annealing furnace
The material is heated in a heat treatment furnace above the recrystallization temperature, and the material is then held at the desired annealing temperature for a suitable period of time before cooling. Once the heating process causes the atomic motion to redistribute and eliminate dislocations in the workpiece, the material recrystallizes as it cools.
Annealing takes place in three stages
1. Recovery Stage - This stage is the use of a furnace or other heating device to raise the temperature of the material to the point where the internal stress can be relieved.
2. Recrystallization stage - Heating the material above its recrystallization temperature but below its melting point causes new grains to form without any residual stress.
3. Grain Growth Stage - Cooling the material at a specific rate results in the creation of new grains, after which the material will be easier to work with, and subsequent operations that alter the mechanical properties can be performed after annealing.
Heat Treatment Annealing Applications and Materials
One of the main applications of heat treatment annealing is to reverse the effects of work hardening. During cold forming, stretching, bending, etc., the material may harden to the point where it cannot be processed further or cause cracking, and annealing operations at this stage will make the material more ductile, allowing for further forming. In a similar manner, annealing is also used to relieve internal stresses that arise when the weld solidifies. In addition to ferrous metals such as steel, other metals may also benefit from annealing, such as a range of non-ferrous metals such as copper, aluminum and brass and several alloys.
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