In this article, we will learn about what exactly is a quenching process? How does this process work? The history behind quenching, etc. So, keep reading this article to know more about the quenching process.
Let’s first start with the definition of the quenching. Quenching is defined as the cooling process in which heated material is cooled down at a faster rate in order to get the desired properties of the metal. Quenching is often known as a rapid cooling process.
History Behind Quenching
Let’s take a brief glance at the history behind quenching. The evidences have revealed that the quenching was in practice since iron age. A historic study has suggested that in Mahabharata oil-quenching was used by warriors in the battle. But the exact study of quenching was started by the Giambattista della Porta. The Giambattista Porta described quenching in his book Magia Naturals in 1558.
In quenching, the cooling medium can be anything like water, oil or air. Quenching also results in increasing the hardness of the steel. If you cool a material quickly then, you don’t have to worry about the formation of the amorphous metal or metallic glass.
Quench hardening is a method in which the strength as well as the hardness of the cast iron and steel alloys is increased by a significant amount. In quench hardening, metals and alloys are heated up to certain temperatures. Then, surface hardening is done to obtain the hard metals which are again tempered to alleviate the brittleness of the metals and alloys.
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What is the Intension Behind applying Quench Hardening?
We always want steel that has a martensitic structure. The steel with martensitic structure is highly useful in various applications. Before quench hardening, the steel and alloy have a pearlitic structure. Such peralitic structure alloys and steels cannot be used for large number of applications. So, in the quench hardening this pearlite is heated up to its eutectoid temperature. Eutectoid temperature is the temperature at which the austenite becomes unstable. This eutectoid temperature is about 727º C. Hence, the austenite structure of steel is converted into martensite at eutectoid temperature.
Exact Process of Quenching
Most of the metals in the quenching process are heated between 715 to 900º C. In the process of heating, it is very important that you must heat the material at a constant temperature. Constant temperature heating results in achieving the desired properties of the metal.
The second thing that you have to done after heating is drenching or we can say soaking. The material or heated workpieces are drenched in the mediums like vacuum or air. The workpieces must be soaked in the salt or sand for 6 minutes and the surrounding temperature must be constant during soaking.
Some of you may think that soaking and cooling are similar. But both soaking and cooling processes are different. Hence after soaking, it is a time to move towards cooling.
In the cooling process, the workpieces have to keep in the quenching liquids. You use water, oil as the quenching mediums. There is a downside of using water as a quenching medium such as it can result in several cracking on the metal surface or it can deform the metal surface. One thing to note down is that cooling rate of oil is much slower than that of the water.
Quenching process can also be practiced in the presence of the inert gases. The inert gases like nitrogen, helium and argon can be used in the quenching process. In this heat treatment process, the quenching medium plays a crucial role. If quenching medium cools at a slower rate than the desired rate then, you will not get the expected properties of the output metal. If quenching medium cools at a faster rate than the desired rate then, you will get cracks on the output metal.
When the quenching process is done you may be noticed that the output material that you are getting may be highly brittle or it may be much harder than normal metal. This is due to the presence of martensite in a large amount in a given material. Hence, you have to apply the process of tempering on such metals. Tempering reduces the unnecessary hardness. For performing tempering, you have to heat the metal below its critical temperature and then, you have to cool this metal in natural air or surrounding.
Types of Quenching
1. Fog Quenching
When quenching process is done in the presence of the mist or vapour then, it is called as a fog quenching.
2. Selective Quenching
When only certain part of metal is gone through quenching then, it is termed as a selective quenching.
3. Direct Quenching
When quenching is practiced with the help of other heat treatment techniques like carburization, etc. then, it is called as a direct quenching.
Thinking about the benefits of the quenching?
There are a lot of advantages of it. Following are the benefits of the quenching process:
- The material that is properly passed through quenching is more durable and has more tensile strength. Hence, quenching enhances the durability of the metal.
- Quenching is a very easy and simple process relative to the other heat treatment processes.
- Quenching takes a very less amount of time and it is the most effective of performed carefully.
Overall, quenching is nothing but a rapid cooling technique where you have to carefully select the quenching mediums. These mediums play an important role in the whole quenching process. This heat treatment technique results in enhancing the strength of the metal as well as its hardness. If you get some valuable knowledge from this article then, don’t hold back yourself from sharing it with your friends and thus, help them in getting the valuable knowledge.