The heat treatment process of the file is as follows: heating → cooling → hot straightening → cooling to room temperature → cleaning → tempering → cleaning → inspection. During the preparation and operation of the heat treatment process, preventing the quenching and decarburization of the teeth and having a skilled straightening technique are the keys to the heat treatment of the file. Therefore, high-frequency induction heating is generally performed, or it is treated in a controlled atmosphere furnace. It can be carried out in a salt bath furnace containing yellow blood salts. The general composition of yellow blood salt is: sodium chloride 50% + yellow blood salt 35% + sodium carbonate 15%. According to the data, the composition of yellow blood salt can fluctuate in the range of 10% to 40% during the actual heating process.

The heat treatment process is as follows:
1. The heating temperature is 750 ~ 790 ℃, and the holding time should be correctly selected according to the different heat treatment equipment.
2. The cooling medium is 10% salt water or flowing water, and the temperature should be lower than 30°C to ensure sufficient cooling performance and high hardness for the file.
3. The low-temperature tempering of the file is usually carried out in a nitrate furnace at a temperature of 160-180 °C and a time of 60-90 minutes.

Notes on heat treatment process:
1. When the file is cooled in the cooling medium to the range of 180-200℃, it should be taken out and straightened by hand immediately. The file is straightened in a short period of time and then placed in the medium to cool through and harden completely.
2. There are four ways to reduce the hardness of the handle: one is to heat the handle in a salt bath furnace for a short time and then cool it in oil; the other is to temper the handle at about 500 ℃ and then cool it in oil; The shank is heated by high-frequency induction; at the end, when quenching and cooling, the teeth of the file first enter the water, and then the whole is cooled when the shank is dark red.
3. Cooling tips for files. When the semi-circular file is cooled, its arc part is easy to bend inward, and it is pre-deformed; For flat files, round files, triangular files and square files, it is placed perpendicular to the liquid surface.
4. The straightening temperature of the file should be correctly controlled, the hardness will be low if the water is discharged early;
To ensure the smooth output of the parts during the heat treatment process, it is an important part of the heat treatment process file.