Introduction to mechanical heat treatment-Jiangmen Xinhui District Meixin Brush Manufacturing Co., Ltd.

　　Steel heat treatment refers to the different heating, heat preservation, and cooling of steel in the 'solid state' to modify the internal structure of the steel, and then obtain the desired structure And function of a skill method.　　In mechanical manufacturing, all important tools and parts must be heat treated, and some parts must be processed more than twice in the entire technical process. In addition to alloying, heat treatment methods are the main way to change the function of metal materials.　　 Heat treatment is different from other processing procedures. Its purpose is not to change the shape and standard of the part, but only to change its internal organization and function. It is an important process to ensure the internal quality of parts. According to the purpose and requirements of the heat treatment and the different technical methods, the heat treatment of steel is classified as follows: 　　 (1) General heat treatment annealing heats the steel to a certain temperature, keeps it for a certain time, and then slowly cools it (following furnace cooling, pit cooling, sand cooling, ash Cold) heat treatment skill is called annealing.　　 Normalizing 　 The heat treatment technology of heating the steel to 30-50 degrees above the phase transition temperature, keeping it for a certain time, and then air cooling.　　 Quenching 　 The steel is heated to a temperature above the phase transition temperature, and then quickly cooled to room temperature (oil-cooled or water-cooled), and then the hardness and wear resistance of the steel are improved.　　 Tempering 　 The quenched workpiece is heated to a temperature lower than the phase transition point for a certain period of time, and then cooled, so that the structure becomes a more stable condition, which is called tempering. Comparison between annealing and normalizing: 　　 Common point: It is mainly used for preliminary heat treatment of casting, forging, and welding blanks to improve the machining function of the blanks, remove internal stress, and prepare for the final heat treatment. It can also be used for machines with low functional requirements. The final heat treatment of the part.　　The difference: the cooling rate is different: the normalizing cooling rate is higher, and the strength and hardness are also higher. Normalizing has a shorter production cycle than annealing and a higher equipment utilization rate, which is more economical.

　　 [Attention] If the standard of the part is large or the shape is messy, normalizing may cause large internal stress and deformation, or even cracking.　　The connection between tempering and quenching: 　　After quenching, although the hardness of steel is high, its brittleness is too large and the structure is unstable, so it is not suitable for direct application. The hardness is reduced by tempering, but the durability is greatly improved. The purpose of tempering is to reduce the brittleness of quenched steel, reduce or eliminate internal stress, and prevent deformation and cracking of the workpiece. Stabilize the unstable organization to maintain the standard accuracy of the shape of the workpiece and obtain the required organization and function.　　 [Attention] Quenching and tempering must be used in cooperation. It is meaningless to perform any operation alone.　　(2) Surface heat treatment 　　surface quenching 　 Surface quenching is a heat treatment method that uses rapid heating to austenitize the surface layer without changing the chemical composition and core structure of the steel to strengthen the surface of the part. At that time, induction heating surface quenching and flame heating surface quenching were widely used in production.　　Chemical heat treatment　 is a heat treatment technique in which steel parts are placed in a specific medium at a certain temperature, so that the active atoms in the medium enter the surface of the steel part, and then the chemical composition and structure of the surface layer are changed to change its function.　　 The methods of chemical heat treatment include: carburizing, nitriding, carbonitriding, chromizing, aluminizing, boronizing, etc.　　 The most commonly used in production at that time were carburizing, nitriding and carbonitriding.