When steel is heated, it changes in terms of electrical resistance, thermal expansion, structure and magnetism. It also relocates atoms, which causes the metal to change properties like hardness and strength.
One of the most common methods used in heat treating is quenching. It is a process that allows you to harden steel without losing its strength or brittleness.
Annealing
When a piece of steel is heated, it changes its physical and chemical properties. This alters the material’s ductility and hardness. It also increases its electrical conductivity.
Annealing is the process of heating metal to a specific temperature and then cooling slowly at a controlled rate. The goal is to soften the metal to improve its workability and reduce its hardness.
During the annealing process, the material’s crystal structure is altered to increase its ductility and decrease its hardness. This change is beneficial for machining, cold working, and other forming processes.
The annealing process also reduces residual stresses in the grains. This can help keep the metal from cracking or breaking after it’s subjected to high-intensity machining.
The annealing process can help strengthen new metal wires that are drawn thinner during machining. It can also strengthen sheet metal that has undergone a stamping or cold drawing process. This is because it removes the residual stress that can cause the metal to break when it’s exposed to high-intensity machining.
Normalizing
When steel is heated, it will begin to change its crystal structure. Depending on the temperature and amount of energy used, different transformations will occur.
The first transformation is called an arrest (A), and occurs when the material stops rising for a short period of time, allowing the temperature to slowly climb again. This allows the crystal to transform and move into a new solid solution, or austenite phase.
Normalizing is one of the simplest heat treatment processes available on investment castings to improve grain structure, machinability and response to subsequent heat-treating operations. It also helps alleviate a problem known as “banding,” which occurs when alloying elements separate during forging or hot rolling.
During the normalizing process, the metal is heated to a higher temperature and then cooled in air. This method of cooling reduces the heating and cooling time compared to furnace cooling. This can make it an attractive option for smaller, less expensive parts that are often produced quickly or that require a faster cooling rate.
Hardening
When steel is heated it goes through a process that changes its chemical makeup. This is known as hardening. It increases the strength and ductility of the metal.
This process is used to make iron-based alloys more durable. However, it can also cause brittleness in the metal.
Tempering is another common heat treatment that helps to reduce brittleness and improves the strength of the metal. This process involves heating the metal to a lower temperature than it is used to, and holding that temperature for a predetermined amount of time.
It is important to remember that the temperature, time and rate of cooling all affect the properties of the metal. It is important to choose the right material for the job and use a qualified heat treating source to ensure that the materials being treated are getting the best results.
Tempering
When a metal is heated, it will change its properties. It may become harder than it needs to be, or it might become brittle.
This is a common problem with steel. After it has been hardened, it is often too brittle to be used in most industrial applications.
Tempering can be used to increase the ductility of hardened steel, which helps it meet its mechanical property requirements. It can also help relieve any internal stresses that may have been introduced during the heating and cooling process of hardening.
The tempering temperature, cooling rate and duration all need to be carefully controlled to achieve the desired results for each application. It is especially important for products that are put under great stress, such as drill bits, springs and even automobile parts like keys or nuts & bolts.
Another heat treatment option is annealing, which is used to release mechanical stresses that are generated by machining and grinding. It can be used for a variety of metals, including aluminium and brass.