What Is an Annealing Service?
An annealing service is a type of heat treatment process that is used to remove internal distortions that occur when metals are hardened.
An annealing service softens the material and improves its ductility, facilitating subsequent processing.
An annealing service refers to complete annealing, but there are other types of annealing services. The annealing service is completed by heating the material to an appropriate temperature and then cooling it slowly. This heat treatment is the opposite of quenching, which hardens the material.
Uses of Annealing Services
An annealing service is often used for products that are cut, forged, or pressed. Automotive parts are a particularly good example. The purpose of annealing service is to facilitate cutting, forging, and press working in subsequent processes.
Without annealing service, the structure of metals and other materials is not uniform, which may lead to deformation or, in the worst case, destruction during subsequent processing. In metals, annealing service restores the crystal structure that has been disrupted by quenching or machining by heating and slow cooling.
Similarly, in semiconductors, different elements such as arsenic and phosphorus are injected into silicon substrates to restore the broken crystal structure, and bonding between doped elements and silicon atoms or between silicon atoms can be created by heat treatment.
Principle of Annealing Services
The purpose of annealing service differs between treatment of metals and treatment of semiconductors. When treating metals, the purpose is to soften the material and make the structure uniform.
On the other hand, when treating semiconductors, the objective is to restore the broken crystal structure.
1. Annealing Services for Metals
The most common annealing service for metals is called “full annealing.” After heating to the region of the austenite phase, which is a homogeneous crystalline layer, the heating equipment is turned off to allow for gradual cooling.
Complete annealing service improves workability and removes internal stresses.
2. Annealing Services for Semiconductors
Broken bonds in semiconductor crystals can be rejoined by applying heat. The reason is that atoms in disordered positions can be shifted to the correct lattice points by applying heat.
Types of Annealing Services
In addition to the complete annealing service described above, the following types of annealing services are available and should be selected according to the application.
1. Isothermal Annealing Service
Isothermal annealing is a technique suitable for softening materials such as tool steel, alloy steel, and high-alloy steel. It includes a cooling process in which the material is fixed at a certain temperature during cooling. Compared to full annealing service, this method is characterized by a shorter working time.
2. Diffusion Annealing Service (Homogenizing)
The purpose of diffusion annealing service is to remove elemental segregation. In steel materials, trace elements such as carbon are added to achieve the required properties, but these elements are significantly segregated in steel materials immediately after solidification, such as after welding.
Diffusion annealing service is used to diffuse the elements by heating the material to make the composition uniform.
3. Spheroidizing Annealing Service
Spheroidizing is used when the carbon concentration in the steel is high. In such steels, the cementite is layered or reticulated, and the workability is not good. By annealing the steel in this condition, the cementite is spherical and evenly dispersed in the material, thus improving workability.
4. Stress Relieving Annealing Service
After heat treatment, machining, and welding, there is always residual stress inside the metal material. If residual stress is left unchecked, deformation of the material will occur when the residual stress is released for some reason.
To remove the strain that causes internal stress, the material is slowly heated to a certain temperature and then slowly cooled so that no distortion occurs.