Flat thread rolling die, also known as rolling wheel, is used to process threads on workpieces on thread rolling machines. The most important characteristics in choosing a rolling die material are the hardness, toughness and wear resistance of the die steel. It must have sufficient hardness and toughness so that the mold can withstand the force applied to it in use; good wear resistance is also necessary, because the main reason for removing the flat thread rolling die from use is due to the The peaks of the threads are worn so that the rolled threads no longer meet the requirements of external dimensions or functions, and cannot continue to be used. Therefore, a good heat treatment level is very important to prompt its quality and life.

Flat thread rolling dies often fail early during use, and the failure forms include thread peeling, edge chipping, piled teeth, premature wear of thread rolling dies, and chipping of tooth shapes, etc., and the average service life is less than 200,000 pieces. The main reason is that surface decarburization, overheating and corrosion are common defects in conventional heat treatment, which seriously reduce the surface hardness, strength, wear resistance and fatigue resistance.
The study found that it is difficult to avoid surface decarburization of the working surface of the thread rolling die if general quenching (such as salt bath furnace quenching) is used, and surface decarburization (or carbon depletion) will cause a significant reduction in the service life of flat thread rolling die. Therefore, vacuum quenching is the best process method. Vacuum heat treatment is carried out in an extremely thin atmosphere, and the pressure in the furnace is generally in the range of 1.33 to 0.13 Pa. The quenching heating and cooling are all completed under the condition of non-oxidation. Decarburization, no carbon increase, bright surface of the workpiece after treatment, small deformation (generally 1/5 of salt bath treatment), long life (generally 3 to 4 times higher than salt bath treatment), and due to the entire quenching process of the thread rolling die All operations are completed in a closed furnace, with a high degree of mechanization and automation, low labor intensity for workers, and no pollution to the environment.
Vacuum heat treatment has the advantages of high quality, low energy consumption, no pollution (or less pollution), etc. It can effectively prevent defects in thread rolling dies, improve surface roughness, and reduce friction factor. Vacuum heating is carried out in the form of radiation, with slow heating, uniform furnace temperature, small product deformation, and dehydrogenation effect, which are conducive to improving the cutting life of flat thread rolling die. The life of vacuum quenching can be increased by 3~ compared with salt furnace quenching. 4 times (average number of rolled pieces). Cutting comparison tests were carried out on thread rolling dies quenched by vacuum furnace, box furnace and salt bath furnace. It can be seen that vacuum heat treatment has the advantages of processing thread rolling die.