Introduction
Low temperature treatment and heat treatment are both essential methods of treating metal. Low temperature treatment can increase toughness and improve strength, while heat treatment can improve hardness, wear resistance, and ductility. In order to understand the principles of these two treatments, it is important to examine the physical and chemical effects these treatments have on metals.
Low Temperature Treatment
Low temperature treatment, which is also known as cryogenic treatment, is a process where metal parts are exposed to very low temperatures in order to improve their physical and chemical properties. Cryogenic treatment results in improved microstructure, increased dimensional stability, improved strength, improved fatigue life, and improved resistance to stress corrosion cracking (SCC). The process also increases the tool’s life and corrects any internal surface defects such as scratches, dents and gouges.
The low temperature treatment process involves first cooling the part to -193C using a cryogenic cooling system. This is followed by a slow warm-up to 0C. During these temperature changes, the chemical and physical properties of the part undergo a change, which is known as tempering. As the part cools, the structure of the metal begins to change. It is important to note that during this process the metal does not become brittle, but instead becomes stronger.
Heat Treatment
Heat treatment is a process which is used to improve the physical and mechanical properties of metals. It can also be used to reduce defects and distortions, as well as enhance the corrosion resistance of certain metals. Heat treatment involves exposing metal parts to temperatures that are higher than normal room temperature. This is done with the aim of altering the microstructure of the part, so that it is more suitable for a given application.
Heat treatment processes can be divided into two main categories: hardening and tempering. In hardening, the metal is heated and cooled rapidly, which causes the molecules to form a hard and dense structure. In tempering, the metal is heated and cooled slowly, which causes the molecules to form a softer and less dense structure.
Other heat treatment processes include annealing, normalizing and quenching. In annealing, the metal is heated slowly, followed by slow cooling. This improves the workability and ductility of the metal. In normalizing, air cooling is used instead of slow cooling, which makes the metal harder and stronger. Quenching is a process where the metal is cooled rapidly in wet or oil baths, resulting in a hard and brittle material.
Equipment
The equipment used for low temperature treatment and heat treatment can vary depending on the type of treatment being applied. For low temperature treatment, cryogenic cooling systems are the most common, which are capable of cooling parts to -193C. Heat treatment, on the other hand, requires an oven or furnace, which can be used to heat parts to temperatures ranging from 500C to more than 1200C, depending on the type of treatment being applied.
Conclusion
Low temperature treatment and heat treatment are two important processes used in treating metals. Low temperature treatment can increase toughness and improve strength, while heat treatment can improve hardness, wear resistance, and ductility. The processes involve the use of cryogenic cooling systems and ovens or furnaces to achieved the desired results, and should always be performed by a qualified engineer.
