Heat Treatment of Shaft Parts
Heat treatment is a process which alters the physical, chemical and mechanical properties of a material. Heat treatment is generally used to improve the performance and safety of a part, but it can also be used for preventive maintenance, for example, to reduce wear resistance or increase hardness. Heat treatment of shaft parts is a process which essentially involves heating the part, cooling it in a controlled manner, and inspecting (and possibly maintaining) the part to ensure it meets the requirements of the end application.
The type of heat treatment applied to any given shaft part depends on the parts basic material composition and the desired outcome of the treatment. Common operations that can be performed on shaft parts during heat treatment include annealing, hardening and tempering, normalizing and carburizing. These operations must be executed according to a carefully planned and executed heat treatment cycle in order to achieve the desired result.
The annealing process is used to reduce the hardness of a material while improving its ductility or plasticity. This process involves heating a part to a temperature that is slightly below its critical temperature and holding it there for a specified time. A controlled cooling process then follows, allowing the part to return to its original austenite state. The purpose of annealing is to reduce or eliminate any internal stress within the material which may have occurred during machining or other manufacturing processes.
Hardening and tempering is a process which increases the hardness of a material. The part is heated to a specific temperature, usually above its critical temperature, and held there for a given period of time. After the required time has elapsed, the part is rapidly cooled. This process will cause the micro-structure of the material to form Martensite, a very hard material. To improve the wear resistance of the part, the hardness may then be reduced by tempering. This is done by heating the part to a lower temperature, usually below its critical temperature, and then cooling it.
Normalizing is a process which is used to refine the micro-structure of a part. The part is heated to a temperature just below its critical temperature and then cooled in still air. This process evens out the distribution of the grain structure, resulting in a much more homogenous material.
Carburizing is a surface treatment that increases the hardness of a material. This process involves heating the part to a relatively low temperature and then introducing a carbon-rich atmosphere. Most commonly, this atmosphere is created by subjecting the part to a gas or a liquid containing carbon in the form of a chemical compound. The part is then left to cool naturally, and the carbon will react with the surface of the part, creating a hard, wear-resistant layer.
In summary, heat treatment is used to alter the physical, chemical and mechanical properties of a material. Heat treatment of shaft parts consists of several sequences of heating, cooling and inspecting operations. The type of treatment applied to a given part is dependent on its base material and the desired outcome. Common operations that are performed on shafts include annealing, hardening and tempering, normalizing and carburizing. All of these operations must be executed according to a carefully designed heat treatment cycle to achieve the desired results.
