Austenitization
Austenitization is the process of heat treating metals to produce a certain microstructure. The process involves heating the metal to a temperature above its transformation temperature, then slowly cooling it. At the correct temperature, the metal will transform from pearlite or ferrite into austenite. Austenitization is a key step in the process of hardening steel, which is the process of increasing steels strength and wear resistance.
When metals are heated, distinct changes occur in their microstructure. The process of austenitization is used to produce a certain microstructure by taking different steps. First, the metal is heated until it reaches its “austenitizing temperature”, which is generally high enough to cause its microstructure to begin to change from its original form. Next, the metal is held at the austenitizing temperature for a set amount of time, or until a desired microstructure is achieved. Finally, the metal is cooled at a controlled rate, allowing the different phases that make up the microstructure to form correctly.
Different materials require different austenitizing temperatures. For example, common carbon steels have an austenitizing temperature of 750 to 900 °C. Although some lower carbon steels may austenize at cooler temperatures, higher carbon steels and more complex alloys require higher temperatures for austenitization. It is also important to note that it is possible to go too far in the process, which can cause unwanted changes in the microstructure of the metal.
Austenitizing and hardening are related processes, but they are two separate steps. Austenitizing is the first step in the hardening process and involves transforming the microstructure of the metal to a form that is strong, hard, and wear resistant. The hardening process itself requires additional steps, such as quickly cooling the metal after austenitizing to transform its austenite into martensite or bainite.
Austenitization can also be used to change the physical and mechanical properties of metals. For example, austenitization can be used to increase the strength and wear resistance of steel, improve the corrosion resistance of stainless steel, and increase the fracture toughness of cast iron.
Austenitization is an important process that can be used to produce high strength and wear resistant metals. By controlling the temperature and cooling rate, it is possible to generate the ideal microstructure for a particular metal. Austenitization is often the fist step in a multi-step hardening process. It can also be used to improve the properties of other metals, such as stainless steel and cast iron.
