Heat treatment for mechanical materials
Heat treatment of materials is the Controlled heating and cooling of the material to the specific temperature for the benefit of changing mechanical properties, physical properties and microstructure of the material that fall in the specified range. It is extensively used for steel and alloy material, aluminum and non ferrous material, plastics and composites and ceramics. It can be also used for manufacturing of components which require toughness, strength and hardness like engine parts, tools and dies.
Heat treatment process can be classified into three main categories; Annealing, Hardening and Tempering.
Annealing process: Annealing process is used to reduce the internal stresses of the material caused by cold working process or other mechanical processing. In this process, the material is heated to specified temperature and held at it for certain period of time and then cooled at the moderate rate in the furnace. After this process, the material becomes soft and ductile. Commonly two annealing processes are done on ferrous materials; process annealing and full annealing. Process annealing is used for reducing the internal stresses of the material and to refine the grain structure to make it machinable. Full annealing is done to restore strength, hardness and machinability of the material.
Hardening process: Hardening process is used to increase the strength and hardness of the material. In this process, the material is heated first to temperature and held at it for certain time period. This process is generally followed by quenching process by which the material is made harder and stronger. Quenching process is done by submerging the material in water or oil bath. After, this process, the hardness of the material increases however it becomes brittle.
Tempering process: Tempering process is used to reduce the brittleness of the material caused due to hardening process. In this process, the material is heated to the specified temperature and held at it for a certain period of time. This tempering of the material restores the ductile characteristics in the material and also reduces the hardness and tensile strength of the material.
Other processes such as carburizing and nitriding are also used to increase the surface hardness of the material. In carburizing process, the internal layer of the material is heated and oxygen is removed from the material. This is followed by the addition of carbon in the material by which the material becomes harder and can also resists wear and tear.
Nitriding process also similar to carburizing process and is used to increase the surface hardness of the material. This process is done in an atmosphere containing nitrogen, which reacts with the material and forms hard surfaces on the material.
All these processes are used for heat treatment of mechanical materials. However, it is important that the process is carried out correctly in order to get the desired properties of the material.
总而言之，机械材料的热处理是通过控制材料加热和冷却到特定温度，以改变其机械性能、物理性能和微观结构。热处理过程可以分为三大类：退火、淬火和回火。退火过程旨在减少材料内部应力，可在钢和合金材料、铝和非铁相金属材料、塑料和复合材料以及陶瓷中使用。淬火的目的是增加材料的强度和硬度，并将其浸入水或油浴中快速冷却。回火用于降低材料的脆性，重新恢复材料的延性和硬度，使其具有较高的机械性能。基于可塑性用相似的完美退火，还可使用渗碳和渗氮等过程来增强材料的表面硬度。因此，对于机械材料的热处理过程，正确的热处理参数至关重要，以获得所需性能。
