Heat treatment hardening is a process used to increase the toughness and strength of metals through the alloying and quenching processes. It involves heating the metal up to its required temperature, holding it at that temperature for a set period of time, cooling it quickly, and then tempering the metal to ensure its optimal properties. Exactly how this process works and which processes are used will be discussed in this article.
Though different metals require different heat treatment temperatures and processes, the goal of hardening a metal is to both increase its strength and toughness and to improve its wear resistance, as well as to improve its machinability. Hardening can also help eliminate structural imperfections, and in certain cases can reduce cracking or other he fissures that might otherwise occur during machining.
The hardening process is often divided into several stages. The first stage of hardening is called alloying, during which the metal is heated to a certain temperature while volatile elements are added to the mix to promote certain beneficial properties. During the cooling process, the elements added during alloying will chemically react with the base metal, producing a stronger and tougher material. This process often takes place in a furnace, using either direct or indirect heating.
Next, the metal needs to be quenched quickly, usually within a few seconds. This is done in order to stop the metallurgical reaction from progressing too quickly and causing cracks and other issues. After quenching, the metal must be tempered. Tempering is a process in which the metal is heated up to a much lower temperature than the quenching temperature, and then held there for a period of time. During this process, some of the strength and hardness in the metal is lost in order to increase toughness and flexibility, which helps to prevent the material from cracking or failing due to a lack of ductility.
Though hardening can be used on most metals, certain metals require more specialized processes in order to achieve the desired characteristics. For example, some high alloy stainless steels will require a double tempering process in order to reach their optimum properties. Also, some harder metals such as tungsten and titanium may require a special quench-and-hold method that allows for a slower rate of cooling in order to reach the desired properties.
Heat treating of metals is an extremely complex process that requires specific temperatures, lengths of time, and procedures in order to achieve the desired results. Each type of metal and its properties must be taken into consideration when determining the best hardening process, as there is no one-size-fits-all approach when it comes to working with the various grades of metal. Heat treating can greatly improve the properties of metals, and depending on the application can make them stronger, tougher, and more resistant to wear and tear. As long as the process is done correctly, the metal should have improved durability and performance.
