Introduction
Heat treatment of steel is a process by which certain physical and mechanical properties of steel are improved by heat. Heat treatment includes the application of heating and cooling cycles to the material in order to achieve desired properties. This involves heating the steel to temperatures of up to 1000°C and then cooling it down slowly or rapidly depending on the desired result. The desired mechanical properties are obtained through a combination of heating, cooling and reheating cycles.
Heat Treatment Parameters
In order to successfully carry out heat treatment of steel, a number of parameters must be taken into consideration. These include the desired transformation temperature, the heating rate, the holding time and the cooling rate. The desired transformation temperature refers to the temperature at which the structural transformation of the steel will take place. During the heating process, the rate at which the temperature increases is known as the heating rate. The amount of time the steel is held at the desired temperature is known as the holding time, and the rate at which the temperature is decreased following the holding time is known as the cooling rate.
Heat Treatment Process
The heat treatment process for steel is generally divided into two main categories: softening and hardening. Softening treatments are used to reduce the hardness and improve the ductility of steel. Common softening treatments include annealing, normalizing and tempering. Hardening treatments are used to improve the hardenability and wear resistance of steel. Common hardening treatments include quenching and tempering.
Annealing
Annealing is the most common softening treatment for steel. This process involves heating the steel to a temperature above its transformation temperature followed by a slow cooling. Annealing is used to reduce the hardness, improve the ductility and increase the formability of steel.
Normalizing
Normalizing is another softening treatment which is similar to annealing but with a slightly higher transformation temperature. Normalizing involves heating the steel to a temperature above the transformation temperature followed by rapid cooling. The rapid cooling increases the hardness of the steel and improves the wear resistance as well.
Tempering
Tempering is a treatment which is used to reduce the brittleness of steel and improve its toughness. Tempering is achieved by heating the steel to a temperature below its transformation temperature followed by a slow cooling.
Quenching
Quenching is a hardening treatment which involves heating the steel to a temperature above its transformation temperature followed by a rapid cooling. Quenching is used to increase the hardness and wear resistance of steel.
Martempering
Martempering is a hardening treatment which is similar to quenching but with a slightly lower transformation temperature. Martempering also involves heating the steel to a temperature above its transformation temperature followed by a rapid cooling. The rapid cooling increases the hardness of the steel and improves the wear resistance.
Conclusion
Heat treatment of steel is a process which is used to improve the physical and mechanical properties of steel. Heat treatment involves heating the steel to temperatures of up to 1000°C followed by cooling it down at certain rates depending on the desired result. There are a number of heat treatment processes which are used to achieve different properties such as annealing, normalizing, tempering, quenching and martempering. By understanding the parameters and process of heat treatment, steel manufacturers can achieve the desired properties in their steel products.
