To perform the quenching process, a metal is heated to a temperature greater than that of normal conditions, typically somewhere above its recrystallization temperature but below its melting temperature. Once the metal has been held at the desired temperature, it is quenched in a medium until it returns to room temperature. The metal also may be quenched for an extended period of time so that the coolness from the quenching process is distributed throughout the thickness of the material.
There are a variety of quenching media available that can perform the quenching process. Each media has its own unique quenching properties. Considerations for the type of media use include quenching speed, quenching media environmental concerns, quenching media replacement, and quenching media cost. Here are the main types of quenching media:. Air is a popular quenching media used to cool metals for quenching. Affordability is one of the main benefits of air; its affordability is a result of its profusion on earth.
In fact, any material that is heated and then allowed to cool to room temperature simply by being left alone is considered to have been air quenched. Air quenching is also more intentionally performed when it is compressed and forced around the metal being quenched.
This cools the part more rapidly than still air, although even compressed air may still cool many metals too slowly to alter the mechanical properties. Oil is able to quench heated metals much more rapidly than compressed air. To quench with oil, a heated part is lowered into a tank that is filled with some type of oil.
The oil can also be flushed through the part. Different types of oil are often used depending on the application because of their varying cooling rates and flash points. Water is able to quench heated metals rapidly as well. What is Tempering 4. Quenching is the process of rapid cooling after the heat treatment of a workpiece. We can do this using water, oil or air.
Quenching is important to obtain material properties of the workpiece. In this process, the undesired low-temperature processes do not occur, i. Moreover, quenching can reduce the crystal grain size of materials, such as metallic object and plastic materials, to increase the hardness. Further, this process is mainly applied for hardening steel. So, we use the process of quenching for this purpose. Tempering is a process that involves heat treating to increase the toughness of iron-based alloys.
Also, this process is very important in removing some of the excessive hardness of steel. In this process, first we need to heat the metal to a temperature below the critical point for some time, and then we need to allow the object to cool in still air. Quenching in caustics dissipates heat so quickly that metal parts are at risk of cracking and warping due to the drastic variation in temperature between the part surface and its core.
Quenching metal in oil is the most popular method because it is relatively severe but with a diminished risk of cracking and warping.
In addition, a wide range of parts quench well in oils because the chemical makeup and temperature of a quenching oil can be adjusted to suit desired end results. These oils are formulated to extend the amount of time during which the highest rate of cooling takes place. Quenching in fast oils is best suited for low-carbon steels and low-alloy parts. Conversely, sometimes cooling needs to be slowed. High-alloy parts with intricate designs quench well in hot oils, as the method reduces the risk of warping and cracking associated with differences in surface and core temperatures.
Quenching in hot oil is a slower process compared to quenching in fast oil. Because oil is flammable, workers must know the flashpoint of the oil in use as well as the load weight and surface area of the products in the workload to avoid fires during quenching.
This means cooling is more controlled and uniform compared to colder, faster and more severe quenches. The hotter the quenchant, the less severe the quench. The less severe the quench, the lower the risk of distortion. Different mixtures of salts have different melting points and working ranges, offering added versatility as a quenching option. Because salts are not flammable, they pose no risk of fire. On the other end of the spectrum, some salt mixtures have high melting points and working ranges and can be used to heat parts.
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