First of all, the tensile strength of the bolt raw material has a great relationship with its quenching process. Generally, it is difficult to meet the raw material requirements of 10.9-level high-strength bolts after 40-degree quenching. If it is not strictly inspected, it can be based on the product after quenching. Surface hardness is used to judge the tensile strength. In addition to the different properties in the processing process, high-strength bolts with different raw materials also have different delay and fracture properties under high pressure.
Secondly, high-strength bolts made of 40Cr quenching treatment are mainly used in bolt ball joint grids. The design strength is generally 390MPa (d>=30mm) or 430MPa (d<30mm). There is no high pre-conditioning during use. Tensile pressure, if a high pre-tension force is to be added, attention should be paid to understanding and ensuring its delayed fracture performance. In order to produce qualified high-strength bolt products, it is best to strictly follow the requirements.
