Abstract: When producing grade 10.9 high-strength bolts with SCM435 steel hot rolled wire rods, the reduction of area of the finished products was lower than the standard requirements. For this quality problem, the composition of the bolts, microstructure and properties were examined, and the microstructures of the defects were examined by SEM-EDS scanning electron microscopy. The reason for the unacceptable bolt shrinkage rate is that there is an M-belt in the center of the bolt, and at the same time, the core M of the hot-rolling coil breaks due to the cold-drawing process, causing crack defects in the core of the bolt. Based on this phenomenon, in order to improve the performance of bolts, relevant tests have been carried out on the quality control of hot-rolled materials and user processes. It was concluded that by reducing the degree of superheat in the steelmaking process, using hot mill rolling for steel rolling, and adopting reasonable cold working and quenching processes by the user, the segregation of the internal components of the rolled material can be effectively reduced, the state of the organization can be improved, To avoid the influence of the hard-phase structure of the core M on cold work and the performance of finished bolts, So as to achieve the purpose of increasing the bolt shrinkage.

Key words: 10.9 high strength bolt, reduction of area, segregation