Processing a DIN 933 bolt, the process is very complicated, after a number of procedures, and strict high-strength bolts of each process can be considered as basically qualified. In order to fully comply with the pre-designed standards, it is necessary to undergo more rigorous tests, as well as reasonable storage, transportation and proper installation, in order to play the real role of a high-strength bolt.
One process in the high-strength bolt manufacturing process is to improve the overall mechanical properties of the fastener, which is the heat treatment process. This process has a very important influence on the intrinsic quality of high-strength bolts, especially high-strength bolts.
With the development of the times, the continuous heat treatment production line with protection after the 1990s has taken the lead. In addition to the excellent sealing performance of the furnace, the temperature and process parameters are very accurate with computer control, and the equipment fault alarm and display functions are also available. During the whole process of quenching and tempering heat treatment, some oxidized gas will be brought from the outside of the furnace. The reaction of a series of chemical changes with the surface rust of the high-strength bolt will cause the high-strength bolt material itself to decarburize. According to the research of the technicians, the decarburization degree of medium carbon alloy steel is more serious than that of carbon steel, and the fastest decarburization temperature is between 700 and 800 degrees Celsius. Mainly because the object attached to the surface of the steel wire decomposes the compound very quickly under certain conditions. If the control of the continuous mesh belt furnace gas is not good, it will also cause the screw decarburization. When the high-strength bolt is used in the cold head forming process, the original material is not only still present in the annealed decarburized layer, but also extruded to the top of the high-strength bolt thread. At this time, the high-strength bolt surface that needs quenching is not obtained. Pre-designed hardness requirements, at this time the mechanical properties of high-strength bolts will be greatly reduced.