The salt bath annealing relieves internal stresses in materials


The salt bath annealing process is a heat treatment that allows the controlled modification of materials’ chemical and physical properties. With it, the material’s malleability is improved by reducing its hardness and increasing its ductility.

It consists of heating the material by placing it above its crystallization temperature, stabilizing the material’s properties at a suitable temperature, and subsequently decreasing said temperature at a specified cooling rate.
This suitable temperature fluctuates from the crystallization temperature to the material’s transformation temperature. This temperature must not exceed the transformation temperature and must always be above the crystallization temperature.
In a salt bath annealing, it is carried out using a dilute salt bath that is the liquid that serves to heat the metallic material. It is a very economical process that is easy to carry out and reliable. Using digital thermometers, the temperature of the salt bath can be controlled.
Why is this process used?
When a material is passed through different processes such as rolling or machining, residual and internal stresses are generated in its molecular structure that affects its characteristics. The salt bath annealing function helps relieve these internal stresses by making the material more flexible and ductile.
There are also industrial processes that require a controlled modification of the microstructure of materials with this efficient process. This allows preparing these modified materials at the microstructure level for subsequent machining or rolling processes. This means that the materials do not suffer cracks during these industrial processes.
Benefits of this process
Materials that are very hard and therefore brittle tend to wear heavily on the tools used for rolling or machining. Consequently, the process of salt bath annealing greatly increases the useful life of tools and equipment and, at the same time, decreases production times.
Salt bath heat treatment can be used on various types of materials such as non-alloyed steels, very low alloyed steels, cast irons, highly alloyed steels, and cast metals; it can even be applied to stainless steels. It is a process widely used today due to its low cost.