Brief introduction of decarburization during heat treatment of high-strength bolts

One of the high-strength bolt manufacturing processes is to improve the comprehensive mechanical properties of fasteners, which is the heat treatment process. This process has a very important influence on the internal quality of high-strength bolts, such as fasteners, especially high-strength bolts.

The process of processing and producing a high-strength bolt is very complicated. After multiple processes, and strictly each kind of high-strength bolt can be regarded as basically qualified. In order to fully comply with the pre-designed standards, more rigorous inspections, reasonable storage, transportation, and correct installation are necessary, and finally the real role of a high-strength bolt can be brought into play. (Guide: Analysis of the causes of damage to high-strength bolts)

Continuous heat treatment production lines with protective effects have taken the lead. In addition to the excellent sealing performance of the furnace, the temperature and process parameters of the quenching and tempering line are very accurate with computer control, and the equipment failure alarm and display functions are also readily available. In the whole process of quenching and tempering heat treatment, some oxidizing gas will be brought from the outside of the furnace. Through a series of chemical changes and the surface rust of the high-strength bolts, it will cause the decarburization of the high-strength bolt material itself. According to the research of technicians, the degree of decarburization 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. The main reason is that the objects attached to the surface of the steel wire decompose compounds very quickly under certain conditions. If the continuous mesh belt furnace gas control is not good, it will also cause the screw decarburization to be excessive. When high-strength bolts are formed by cold heading, the annealed decarburized layer of the original material not only still exists, but also is extruded to the top of the high-strength bolt threads. At this time, the surface of the high-strength bolt that needs to be quenched is not available. With the pre-designed hardness requirements, the mechanical properties of high-strength bolts will be greatly reduced at this time.

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