Heat Treatment of Bearing Components (Part I)
Heat treatment of bearing components is an important step in ensuring their long-term performance and wear-resistance. Bearing components, such as axles, pins, and bushings, are designed to withstand intense loads and friction, so they must be treated with precise thermal operations in order to increase their strength and extend their service life.
The most common heat treatment processes used on bearing components are annealing, quenching, and tempering. Each of these processes serves to alter the microstructure of the materials used to fabricate the bearing components, thereby improving their functional properties and increasing their longevity.
In the annealing process, the bearing components are heated – generally to a point in between their recrystallization and melting temperatures — and then left to cool slowly in order to reduce the amount of strain that the alloy has endured during its processing. This serves to remove internal stresses and increase the overall strength of the metal components. It is important to note that annealing is typically followed by a process called normalizing in order to improve the ductility of the workpiece.
In the quenching process, the components are rapidly cooled in a medium such as oil, water, or air. The rapid cooling allows for a hardening of the metal’s surface, where the widened grain structure is diminished and hardened crystals form. Quenching is most commonly applied to bearing components made from steel, though it is also sometimes used on components featuring an alloy.
Finally, the tempering process is used to reduce the brittleness of components made from steel. In this process, the components are heated to between 350 and 650 degrees Fahrenheit before being cooled slowly in a process called “aging” or “low tempering.” This allows the components to retain their strength while adding some flexibility, allowing them to better resist cracking or breaking during use.
In addition to the above-mentioned processes, many bearing components also require additional treatments such as case hardening, nitriding, and carburizing. Case hardening, or “surface hardening,” is the process by which a hard outer layer is created by selectively applying heat to the surface of the bearing components. Nitriding involves the introduction of nitrogen into the metal alloy, resulting in improved fatigue strength and corrosion resistance. Lastly, carburizing is used to increase strength and wear resistance by introducing additional carbon molecules, resulting in a harder and more durable bearing surface.
By performing these thermal treatments correctly and in the appropriate sequence, bearing components can be significantly improved both in terms of strength and service life. In the next installment of this article we will examine in more detail the many benefits of heat treatment for bearing components.
