The Physical Properties of Heat Treated Steel
Steel is one of the most important materials used in modern engineering. Its strength, toughness, and ductility depend on its composition and heat treatment. Heat treating is the process of heating and cooling metals in order to change its physical and mechanical properties. Heat treating steel can be used to increase the strength of the material, to improve its machinability, and to alter its structure in order to make it more resistant to corrosion. In this paper, we will discuss the physical properties of steel that can be altered through heat treatment and how these altered properties affect the applications of the material.
The most common method of heat treating steel is quenching and tempering. Quenching involves rapidly cooling the steel either in an oil bath or by immersion in water. Tempering involves reheating the steel to a lower temperature for a period of time before cooling. Quenching and tempering are done in order to increase the hardness, strength, and toughness of the steel. The rapid cooling of the quenching process results in the production of martensite, a form of hard and brittle microstructure. The tempering process helps relieve some of the stresses from the quenching process and increases the ductility of the material while still preserving the increased hardness and strength.
Another effect of heat treating is in the alteration of the microstructure of the steel. By controlling the cooling rate during heat treating, the size, shape, and distribution of the grains in the steel can be changed. This change in microstructure can drastically increase the strength, as well as the corrosion resistance, of the material.
Heat treating can also be used to reduce the amount of internal stresses in the material. These stresses can be caused by welding, machining, and even from the forces of forming the metal. Stress relieving treatments such as annealing and normalizing can be used to reduce these internal stresses and increase the ductility of the metal to prevent cracking or failure.
Finally, heat treating can also be used to create specific microstructures in the steel by using intermediate cooling processes. These microstructures can be used to enhance the properties of the material for specific applications. For example, a specific microstructure can be created to give the steel a higher resistance to wear, or it can be created to improve its machinability.
In conclusion, heat treating can be used to drastically alter the physical and mechanical properties of steel. Quenching and tempering are the most common methods of heat treating steel, and can be used to increase the strength and toughness of the material. Heat treating can also be used to alter the microstructure of the steel, reduce internal stresses, and to create specific microstructures for specific applications. The versatility of heat treating allows for the steel to be manipulated and optimized for specific applications, making it one of the most important materials in modern engineering.
